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Distribution
Flatfishes are found in oceans worldwide, ranging from the Arctic, through the tropics, to Antarctica. Species diversity is centered in the Indo-West Pacific and declines following both latitudinal and longitudinal gradients away from the Indo-West Pacific. Most species are found in depths between 0 and , but a few have been recorded from depths in excess of . None have been confirmed from the abyssal or hadal zones. An observation of a flatfish from the Bathyscaphe Trieste at the bottom of the Mariana Trench at a depth of almost has been questioned by fish experts, and recent authorities do not recognize it as valid. Among the deepwater species, Symphurus thermophilus lives congregating around "ponds" of sulphur at hydrothermal vents on the seafloor. No other flatfish is known from hydrothermal vents. Many species will enter brackish or fresh water, and a smaller number of soles (families Achiridae and Soleidae) and tonguefish (Cynoglossidae) are entirely restricted to fresh water.
Characteristics
The most obvious characteristic of the flatfish is its asymmetry, with both eyes lying on the same side of the head in the adult fish. In some families, the eyes are usually on the right side of the body (dextral or right-eyed flatfish), and in others, they are usually on the left (sinistral or left-eyed flatfish). The primitive spiny turbots include equal numbers of right- and left-sided individuals, and are generally less asymmetrical than the other families. Other distinguishing features of the order are the presence of protrusible eyes, another adaptation to living on the seabed (benthos), and the extension of the dorsal fin onto the head.
The most basal members of the group, the threadfins, do not closely resemble the flatfishes.
The surface of the fish facing away from the sea floor is pigmented, often serving to camouflage the fish, but sometimes with striking coloured patterns. Some flatfishes are also able to change their pigmentation to match the background, in a manner similar to some cephalopods. The side of the body without the eyes, facing the seabed, is usually colourless or very pale. | Flatfish | Wikipedia | 475 | 46331 | https://en.wikipedia.org/wiki/Flatfish | Biology and health sciences | Acanthomorpha | null |
In general, flatfishes rely on their camouflage for avoiding predators, but some have aposematic traits such as conspicuous eyespots (e.g., Microchirus ocellatus) and several small tropical species (at least Aseraggodes, Pardachirus and Zebrias) are poisonous. Juveniles of Soleichthys maculosus mimic toxic flatworms of the genus Pseudobiceros in both colours and swimming mode. Conversely, a few octopus species have been reported to mimic flatfishes in colours, shape and swimming mode.
The flounders and spiny turbots eat smaller fish, and have well-developed teeth. They sometimes seek prey in the midwater, away from the bottom, and show fewer extreme adaptations than other families. The soles, by contrast, are almost exclusively bottom-dwellers, and feed on invertebrates. They show a more extreme asymmetry, and may lack teeth on one side of the jaw.
Flatfishes range in size from Tarphops oligolepis, measuring about in length, and weighing , to the Atlantic halibut, at and .
Species and species groups
Brill
Dab
Sanddab
Flounder
Halibut
Megrim
Plaice
Sole
Tonguefish
Turbot
Reproduction
Flatfishes lay eggs that hatch into larvae resembling typical, symmetrical, fish. These are initially elongated, but quickly develop into a more rounded form. The larvae typically have protective spines on the head, over the gills, and in the pelvic and pectoral fins. They also possess a swim bladder, and do not dwell on the bottom, instead dispersing from their hatching grounds as plankton.
The length of the planktonic stage varies between different types of flatfishes, but eventually they begin to metamorphose into the adult form. One of the eyes migrates across the top of the head and onto the other side of the body, leaving the fish blind on one side. The larva also loses its swim bladder and spines, and sinks to the bottom, laying its blind side on the underlying surface. | Flatfish | Wikipedia | 428 | 46331 | https://en.wikipedia.org/wiki/Flatfish | Biology and health sciences | Acanthomorpha | null |
Origin and evolution
Scientists have been proposing since the 1910s that flatfishes evolved from percoid ancestors. There has been some disagreement whether they are a monophyletic group. Some palaeontologists think that some percomorph groups other than flatfishes were "experimenting" with head asymmetry during the Eocene, and certain molecular studies conclude that the primitive family of Psettodidae evolved their flat bodies and asymmetrical head independently of other flatfish groups. Many scientists, however, argue that pleuronectiformes are monophyletic.
The fossil record indicates that flatfishes might have been present before the Eocene, based on fossil otoliths resembling those of modern pleuronectiforms dating back to the Thanetian and Ypresian stages (57-53 million years ago).
Flatfishes have been cited as dramatic examples of evolutionary adaptation. Richard Dawkins, in The Blind Watchmaker, explains the flatfishes' evolutionary history thus:
...bony fish as a rule have a marked tendency to be flattened in a vertical direction.... It was natural, therefore, that when the ancestors of [flatfish] took to the sea bottom, they should have lain on one side.... But this raised the problem that one eye was always looking down into the sand and was effectively useless. In evolution this problem was solved by the lower eye 'moving' round to the upper side. | Flatfish | Wikipedia | 301 | 46331 | https://en.wikipedia.org/wiki/Flatfish | Biology and health sciences | Acanthomorpha | null |
The origin of the unusual morphology of flatfishes was enigmatic up to the 2000s, and early researchers suggested that it came about as a result of saltation rather than gradual evolution through natural selection, because a partially migrated eye were considered to have been maladaptive. This started to change in 2008 with a study on the two fossil genera Amphistium and Heteronectes, dated to about 50 million years ago. These genera retain primitive features not seen in modern types of flatfishes. In addition, their heads are less asymmetric than modern flatfishes, retaining one eye on each side of their heads, although the eye on one side is closer to the top of the head than on the other. The more recently described fossil genera Quasinectes and Anorevus have been proposed to show similar morphologies and have also been classified as "stem pleuronectiforms". Suchs findings lead Friedman to conclude that the evolution of flatfish morphology "happened gradually, in a way consistent with evolution via natural selection—not suddenly, as researchers once had little choice but to believe."
To explain the survival advantage of a partially migrated eye, it has been proposed that primitive flatfishes like Amphistium rested with the head propped up above the seafloor (a behaviour sometimes observed in modern flatfishes), enabling them to use their partially migrated eye to see things closer to the seafloor.
While known basal genera like Amphistium and Heteronectes support a gradual acquisition of the flatfish morphology, they were probably not direct ancestors to living pleuronectiforms, as fossil evidence indicate that most flatfish lineages living today were present in the Eocene and contemporaneous with them. It has been suggested that the more primitive forms were eventually outcompeted.
As food
Flatfish is considered a Whitefish because of the high concentration of oils within its liver. Its lean flesh makes for a unique flavor that differs from species to species. Methods of cooking include grilling, pan-frying, baking and deep-frying.
Timeline of genera | Flatfish | Wikipedia | 428 | 46331 | https://en.wikipedia.org/wiki/Flatfish | Biology and health sciences | Acanthomorpha | null |
A passerine () is any bird of the order Passeriformes (; from Latin 'sparrow' and '-shaped') which includes more than half of all bird species. Sometimes known as perching birds, passerines generally have an anisodactyl arrangement of their toes (three pointing forward and one back), which facilitates perching.
With more than 140 families and some 6,500 identified species, Passeriformes is the largest order of birds and among the most diverse clades of terrestrial vertebrates, representing 60% of birds. Passerines are divided into three suborders: New Zealand wrens; diverse birds found only in North and South America; and songbirds. Passerines originated in the Southern Hemisphere around 60 million years ago.
Most passerines are insectivorous or omnivorous, and eat both insects and fruit or seeds.
Etymology
The terms "passerine" and "Passeriformes" are derived from the scientific name of the house sparrow, Passer domesticus, whose genus is the Latin word for sparrow. Formerly this meant the songbirds of Europe. Now it also includes perching, non-singing birds from the Americas.
Description
The order is divided into three suborders, Tyranni (non-singing, Americas), Passeri (songbirds), and the basal New Zealand wrens. Oscines have the best control of their syrinx muscles among birds, producing a wide range of songs and other vocalizations, though some of them, such as the crows, do not sound musical to human beings. Some, such as the lyrebird, are accomplished mimics. The New Zealand wrens are tiny birds restricted to New Zealand, at least in modern times; they were long placed in Passeri.
Most passerines are smaller than typical members of other avian orders. The heaviest and altogether largest passerines are the thick-billed raven and the larger races of common raven, each exceeding and . The superb lyrebird and some birds-of-paradise, due to very long tails or tail coverts, are longer overall. The smallest passerine is the short-tailed pygmy tyrant, at and . | Passerine | Wikipedia | 453 | 46336 | https://en.wikipedia.org/wiki/Passerine | Biology and health sciences | Passerines | null |
Anatomy
The foot of a passerine has three toes directed forward and one toe directed backward, called anisodactyl arrangement. The hind toe (hallux) is long and joins the leg at approximately the same level as the front toes. This arrangement enables passerine birds to easily perch upright on branches. The toes have no webbing or joining, but in some cotingas, the second and third toes are united at their basal third.
The leg of passerine birds contains an additional special adaptation for perching. A tendon in the rear of the leg running from the underside of the toes to the muscle behind the tibiotarsus will automatically be pulled and tighten when the leg bends, causing the foot to curl and become stiff when the bird lands on a branch. This enables passerines to sleep while perching without falling off.
Most passerine birds have 12 tail feathers but the superb lyrebird has 16, and several spinetails in the family Furnariidae have 10, 8, or even 6, as is the case of Des Murs's wiretail. Species adapted to tree trunk climbing such as treecreepers and woodcreeper have stiff tail feathers that are used as props during climbing. Extremely long tails used as sexual ornaments are shown by species in different families. A well-known example is the long-tailed widowbird.
Eggs and nests
The chicks of passerines are altricial: blind, featherless, and helpless when hatched from their eggs. Hence, the chicks require extensive parental care. Most passerines lay colored eggs, in contrast with nonpasserines, most of whose eggs are white except in some ground-nesting groups such as Charadriiformes and nightjars, where camouflage is necessary, and in some parasitic cuckoos, which match the passerine host's egg. The vinous-throated parrotbill has two egg colors, white and blue, to deter the brood parasitic common cuckoo.
Clutches vary considerably in size: some larger passerines of Australia such as lyrebirds and scrub-robins lay only a single egg, most smaller passerines in warmer climates lay between two and five, while in the higher latitudes of the Northern Hemisphere, hole-nesting species like tits can lay up to a dozen and other species around five or six.
The family Viduidae do not build their own nests, instead, they lay eggs in other birds' nests. | Passerine | Wikipedia | 499 | 46336 | https://en.wikipedia.org/wiki/Passerine | Biology and health sciences | Passerines | null |
The Passeriformes contain several groups of brood parasites such as the viduas, cuckoo-finches, and the cowbirds.
Origin and evolution
The evolutionary history of the passerine families and the relationships among them remained rather mysterious until the late 20th century. In many cases, passerine families were grouped together on the basis of morphological similarities that, it is now believed, are the result of convergent evolution, not a close genetic relationship. For example, the wrens of the Americas and Eurasia, those of Australia, and those of New Zealand look superficially similar and behave in similar ways, yet belong to three far-flung branches of the passerine family tree; they are as unrelated as it is possible to be while remaining Passeriformes.
Advances in molecular biology and improved paleobiogeographical data gradually are revealing a clearer picture of passerine origins and evolution that reconciles molecular affinities, the constraints of morphology, and the specifics of the fossil record. The first passerines are now thought to have evolved in the Southern Hemisphere in the late Paleocene or early Eocene, around 50 million years ago.
The initial diversification of passerines coincides with the separation of the southern continents in the early Eocene. The New Zealand wrens are the first to become isolated in Zealandia, and the second split involved the origin of the Tyranni in South America and the Passeri in the Australian continent. The Passeri experienced a great radiation of forms in Australia. A major branch of the Passeri, the parvorder Passerida, dispersed into Eurasia and Africa about 40 million years ago, where they experienced further radiation of new lineages. This eventually led to three major Passerida lineages comprising about 4,000 species, which in addition to the Corvida and numerous minor lineages make up songbird diversity today. Extensive biogeographical mixing happens, with northern forms returning to the south, southern forms moving north, and so on.
Fossil record
Earliest passerines | Passerine | Wikipedia | 414 | 46336 | https://en.wikipedia.org/wiki/Passerine | Biology and health sciences | Passerines | null |
Perching bird osteology, especially of the limb bones, is rather diagnostic. However, the early fossil record is poor because passerines are relatively small, and their delicate bones do not preserve well. Queensland Museum specimens F20688 (carpometacarpus) and F24685 (tibiotarsus) from Murgon, Queensland, are fossil bone fragments initially assigned to Passeriformes. However, the material is too fragmentary and their affinities have been questioned. Several more recent fossils from the Oligocene of Europe, such as Wieslochia, Jamna, Resoviaornis, and Crosnoornis, are more complete and definitely represent early passeriforms, and have been found to belong to a variety of modern and extinct lineages.
From the Bathans Formation at the Manuherikia River in Otago, New Zealand, MNZ S42815 (a distal right tarsometatarsus of a tui-sized bird) and several bones of at least one species of saddleback-sized bird have recently been described. These date from the Early to Middle Miocene (Awamoan to Lillburnian, 19–16 mya).
Early European passerines | Passerine | Wikipedia | 256 | 46336 | https://en.wikipedia.org/wiki/Passerine | Biology and health sciences | Passerines | null |
In Europe, perching birds are not too uncommon in the fossil record from the Oligocene onward, belonging to several lineages:
Wieslochia (Early Oligocene of Frauenweiler, Germany) – suboscine
Resoviaornis (Early Oligocene of Wola Rafałowska, Poland) – oscine
Jamna (Early Oligocene of Jamna Dolna, Poland) – basal
Winnicavis (Early Oligocene of Lower Silesian Voivodeship, Poland)
Crosnoornis (Early Oligocene of Poland) - suboscine
Passeriformes gen. et sp. indet. (Early Oligocene of Luberon, France) – suboscine or basal
Passeriformes gen. et spp. indet. (Late Oligocene of France) – several suboscine and oscine taxa
Passeriformes gen. et spp. indet. (Middle Miocene of France and Germany) – basal?
Passeriformes gen. et spp. indet. (Sajóvölgyi Middle Miocene of Mátraszőlős, Hungary) – at least 2 taxa, possibly 3; at least one probably Oscines.
Passeriformes gen. et sp. indet. (Middle Miocene of Felsőtárkány, Hungary) – oscine?
Passeriformes gen. et sp. indet. (Late Miocene of Polgárdi, Hungary) – Sylvioidea (Sylviidae? Cettiidae?)
That suboscines expanded much beyond their region of origin is proven by several fossils from Germany such as a presumed broadbill (Eurylaimidae) humerus fragment from the Early Miocene (roughly 20 mya) of Wintershof, Germany, the Late Oligocene carpometacarpus from France listed above, and Wieslochia, among others. Extant Passeri super-families were quite distinct by that time and are known since about 12–13 mya when modern genera were present in the corvoidean and basal songbirds. The modern diversity of Passerida genera is known mostly from the Late Miocene onward and into the Pliocene (about 10–2 mya). Pleistocene and early Holocene lagerstätten (<1.8 mya) yield numerous extant species, and many yield almost nothing but extant species or their chronospecies and paleosubspecies.
American fossils | Passerine | Wikipedia | 509 | 46336 | https://en.wikipedia.org/wiki/Passerine | Biology and health sciences | Passerines | null |
In the Americas, the fossil record is more scant before the Pleistocene, from which several still-existing families are documented. Apart from the indeterminable MACN-SC-1411 (Pinturas Early/Middle Miocene of Santa Cruz Province, Argentina), an extinct lineage of perching birds has been described from the Late Miocene of California, United States: the Palaeoscinidae with the single genus Palaeoscinis. "Palaeostruthus" eurius (Pliocene of Florida) probably belongs to an extant family, most likely passeroidean.
Systematics and taxonomy
The Passeriformes is currently divided into three suborders: Acanthisitti (New Zealand wrens), Tyranni, (suboscines) and Passeri (oscines or songbirds). The Passeri is now subdivided into two major groups recognized now as Corvides and Passerida respectively containing the large superfamilies Corvoidea and Meliphagoidea, as well as minor lineages, and the superfamilies Sylvioidea, Muscicapoidea, and Passeroidea but this arrangement has been found to be oversimplified. Since the mid-2000s, studies have investigated the phylogeny of the Passeriformes and found that many families from Australasia traditionally included in the Corvoidea actually represent more basal lineages within oscines. Likewise, the traditional three-superfamily arrangement within the Passeri has turned out to be far more complex and will require changes in classification. | Passerine | Wikipedia | 335 | 46336 | https://en.wikipedia.org/wiki/Passerine | Biology and health sciences | Passerines | null |
Major "wastebin" families such as the Old World warblers and Old World babblers have turned out to be paraphyletic and are being rearranged. Several taxa turned out to represent highly distinct lineages, so new families had to be established, some of these – like the stitchbird of New Zealand and the Eurasian bearded reedling – monotypic with only one living species. In the Passeri alone, a number of minor lineages will eventually be recognized as distinct superfamilies. For example, the kinglets constitute a single genus with less than 10 species today but seem to have been among the first perching bird lineages to diverge as the group spread across Eurasia. No particularly close relatives of theirs have been found among comprehensive studies of the living Passeri, though they might be fairly close to some little-studied tropical Asian groups. Nuthatches, wrens, and their closest relatives are currently grouped in a distinct super-family Certhioidea.
Taxonomic list of Passeriformes families
This list is in taxonomic order, placing related families next to one another. The families listed are those recognised by the International Ornithologists' Union (IOC). The order and the division into infraorders, parvorders, and superfamilies follows the phylogenetic analysis published by Carl Oliveros and colleagues in 2019. The relationships between the families in the suborder Tyranni (suboscines) were all well determined but some of the nodes in Passeri (oscines or songbirds) were unclear owing to the rapid splitting of the lineages.
Suborder Acanthisitti
Acanthisittidae: New Zealand wrens
Suborder Tyranni (suboscines)
Infraorder Eurylaimides: Old World suboscines
Infraorder Tyrannides: New World suboscines
Parvorder Furnariida
Parvorder Tyrannida
Suborder Passeri (oscines or songbirds) | Passerine | Wikipedia | 418 | 46336 | https://en.wikipedia.org/wiki/Passerine | Biology and health sciences | Passerines | null |
Atrichornithidae: scrub-birds
Menuridae: lyrebirds
Climacteridae: Australian treecreepers
Ptilonorhynchidae: bowerbirds
Pomatostomidae: pseudo-babblers
Orthonychidae: logrunners
Superfamily Meliphagoidea
Acanthizidae: scrubwrens, thornbills, and gerygones
Meliphagidae: honeyeaters
Maluridae: fairywrens, emu-wrens and grasswrens
Dasyornithidae: bristlebirds
Pardalotidae: pardalotes
Infraorder Corvides – previously known as the parvorder Corvida
Cinclosomatidae: jewel-babblers, quail-thrushes
Campephagidae: cuckooshrikes and trillers
Mohouidae: whiteheads
Neosittidae: sittellas
Superfamily Orioloidea
Psophodidae: whipbirds
Eulacestomatidae: wattled ploughbill
Falcunculidae: shriketit
Oreoicidae: Australo-Papuan bellbirds
Paramythiidae: painted berrypeckers
Vireonidae: vireos
Pachycephalidae: whistlers
Oriolidae: Old World orioles and figbirds
Superfamily Malaconotoidea
Machaerirhynchidae: boatbills
Artamidae: woodswallows, butcherbirds, currawongs, and Australian magpie
Rhagologidae: mottled berryhunter
Malaconotidae: puffback shrikes, bush shrikes, tchagras, and boubous
Pityriaseidae: bristlehead
Aegithinidae: ioras
Platysteiridae: wattle-eyes and batises
Vangidae: vangas
Superfamily Corvoidea
Rhipiduridae: fantails
Dicruridae: drongos
Monarchidae: monarch flycatchers
Ifritidae: blue-capped ifrit
Paradisaeidae: birds-of-paradise
Corcoracidae: white-winged chough and apostlebird
Melampittidae: melampittas
Laniidae: shrikes
Platylophidae: jayshrike
Corvidae: crows, ravens, and jays | Passerine | Wikipedia | 475 | 46336 | https://en.wikipedia.org/wiki/Passerine | Biology and health sciences | Passerines | null |
Infraorder Passerides – previously known as the parvorder Passerida
Cnemophilidae: satinbirds
Melanocharitidae: berrypeckers and longbills
Callaeidae: New Zealand wattlebirds
Notiomystidae: stitchbird
Petroicidae: Australian robins
Eupetidae: rail-babbler
Picathartidae: rockfowl
Chaetopidae: rock-jumpers
Parvorder Sylviida – previously known as the superfamily Sylviodea
Hyliotidae: hyliotas
Stenostiridae: fairy flycatchers
Paridae: tits, chickadees and titmice
Remizidae: penduline tits
Panuridae: bearded reedling
Alaudidae: larks
Nicatoridae: nicators
Macrosphenidae: crombecs and African warblers
Cisticolidae: cisticolas and allies
Superfamily Locustelloidea
Acrocephalidae: reed warblers, Grauer's warbler and allies
Locustellidae: grassbirds and allies
Donacobiidae: black-capped donacobius
Bernieridae: Malagasy warblers
—
Pnoepygidae: wren-babblers
Hirundinidae: swallows and martins
Superfamily Sylvioidea
Pycnonotidae: bulbuls
Sylviidae: sylviid babblers
Paradoxornithidae: parrotbills and myzornis
Zosteropidae: white-eyes
Timaliidae: tree babblers
Leiothrichidae: laughingthrushes and allies
Alcippeidae: Alcippe fulvettas
Pellorneidae: ground babblers
Superfamily Aegithaloidea
Phylloscopidae: leaf-warblers and allies
Hyliidae: hylias
Aegithalidae: long-tailed tits or bushtits
Scotocercidae: streaked scrub warbler
Cettiidae: Cettia bush warblers and allies
Erythrocercidae: yellow flycatchers
Parvorder Muscicapida – previously known as the superfamily Muscicapoidea
Superfamily Bombycilloidea
Dulidae: palmchat
Bombycillidae: waxwings
Ptiliogonatidae: silky flycatchers
Hylocitreidae: hylocitrea
Hypocoliidae: hypocolius
†Mohoidae: oos | Passerine | Wikipedia | 510 | 46336 | https://en.wikipedia.org/wiki/Passerine | Biology and health sciences | Passerines | null |
Superfamily Muscicapoidea
Elachuridae: spotted elachura
Cinclidae: dippers
Muscicapidae: Old World flycatchers and chats
Turdidae: thrushes and allies
Buphagidae: oxpeckers
Sturnidae: starlings and rhabdornis
Mimidae: mockingbirds and thrashers
—
Regulidae: goldcrests and kinglets
Superfamily Certhioidea
Tichodromidae: wallcreeper
Sittidae: nuthatches
Certhiidae: treecreepers
Polioptilidae: gnatcatchers
Troglodytidae: wrens
Parvorder Passerida – previously known as the superfamily Passeroidea
Promeropidae: sugarbirds
Modulatricidae: dapple-throat and allies
Nectariniidae: sunbirds
Dicaeidae: flowerpeckers
Chloropseidae: leafbirds
Irenidae: fairy-bluebirds
Peucedramidae: olive warbler
Urocynchramidae: Przewalski's finch
Ploceidae: weavers
Viduidae: indigobirds and whydahs
Estrildidae: waxbills, munias and allies
Prunellidae: accentors
Passeridae: Old World sparrows and snowfinches
Motacillidae: wagtails and pipits
Fringillidae: finches and euphonias
Superfamily Emberizoidea – previously known as the New World nine-primaried oscines
Rhodinocichlidae: rosy thrush-tanager
Calcariidae: longspurs and snow buntings
Emberizidae: buntings
Cardinalidae: cardinals
Mitrospingidae: mitrospingid tanagers
Thraupidae: tanagers and allies
Passerellidae: New World sparrows, bush tanagers
Parulidae: New World warblers
Icteriidae: yellow-breasted chat
Icteridae: grackles, New World blackbirds, and New World orioles
Calyptophilidae: chat-tanagers
Zeledoniidae: wrenthrush
Teretistridae: Cuban warblers
Nesospingidae: Puerto Rican tanager
Spindalidae: spindalises
Phaenicophilidae: Hispaniolan tanagers | Passerine | Wikipedia | 483 | 46336 | https://en.wikipedia.org/wiki/Passerine | Biology and health sciences | Passerines | null |
Phylogeny
Relationships between living Passeriformes families based on the phylogenetic analysis of Oliveros et al (2019). Some terminals have been renamed to reflect families recognised by the IOC but not in that study. The IOC families Alcippeidae and Teretistridae were not sampled in this study.
Explanatory notes | Passerine | Wikipedia | 69 | 46336 | https://en.wikipedia.org/wiki/Passerine | Biology and health sciences | Passerines | null |
Phalangeriformes is a paraphyletic suborder of about 70 species of small to medium-sized arboreal marsupials native to Australia, New Guinea, and Sulawesi. The species are commonly known as possums, opossums, gliders, and cuscus. The common name "(o)possum" for various Phalangeriformes species derives from the creatures' resemblance to the opossums of the Americas (the term comes from Powhatan language aposoum "white animal", from Proto-Algonquian *wa·p-aʔɬemwa "white dog"). However, although opossums are also marsupials, Australasian possums are more closely related to other Australasian marsupials such as kangaroos.
Phalangeriformes are quadrupedal diprotodont marsupials with long tails. The smallest species, indeed the smallest diprotodont marsupial, is the Tasmanian pygmy possum, with an adult head-body length of and a weight of . The largest are the two species of bear cuscus, which may exceed . Phalangeriformes species are typically nocturnal and at least partially arboreal. They inhabit most vegetated habitats, and several species have adjusted well to urban settings. Diets range from generalist herbivores or omnivores (the common brushtail possum) to specialist browsers of eucalyptus (greater glider), insectivores (mountain pygmy possum) and nectar-feeders (honey possum).
Classification
About two-thirds of Australian marsupials belong to the order Diprotodontia, which is split into three suborders, namely the Vombatiformes (wombats and the koala, four species in total); the large and diverse Phalangeriformes (the possums and gliders) and Macropodiformes (kangaroos, potoroos, wallabies and the musky rat-kangaroo). Note: this classification is based on Ruedas & Morales 2005. However, Phalangeriformes has been recovered as paraphyletic with respect to Macropodiformes, rendering the latter a subset of the former if Phalangeriformes are to be considered a natural group. | Phalangeriformes | Wikipedia | 488 | 46371 | https://en.wikipedia.org/wiki/Phalangeriformes | Biology and health sciences | Diprotodontia | Animals |
Suborder Phalangeriformes: possums, gliders and allies
Superfamily Phalangeroidea
Family †Ektopodontidae:
Genus †Ektopodon
†Ektopodon serratus
†Ektopodon stirtoni
†Ektopodon ulta
Family Burramyidae: (pygmy possums)
Genus Burramys
Mountain pygmy possum, B. parvus
Genus Cercartetus
Long-tailed pygmy possum, C. caudatus
Southwestern pygmy possum, C. concinnus
Tasmanian pygmy possum, C. lepidus
Eastern pygmy possum, C. nanus
Family Phalangeridae: (brushtail possums and cuscuses)
Subfamily Ailuropinae
Genus Ailurops
Talaud bear cuscus, A. melanotis
Sulawesi bear cuscus, A. ursinus
Genus Strigocuscus
Sulawesi dwarf cuscus, S. celebensis
Banggai cuscus, S. pelegensis
Subfamily Phalangerinae
Tribe Phalangerini
Genus Phalanger
Gebe cuscus, P. alexandrae
Mountain cuscus, P. carmelitae
Ground cuscus, P. gymnotis
Eastern common cuscus, P. intercastellanus
Woodlark cuscus, P. lullulae
Blue-eyed cuscus, P. matabiru
Telefomin cuscus, P. matanim
Southern common cuscus, P. mimicus
Northern common cuscus, P. orientalis
Ornate cuscus, P. ornatus
Rothschild's cuscus, P. rothschildi
Silky cuscus, P. sericeus
Stein's cuscus, P. vestitus
Genus Spilocuscus
Admiralty Island cuscus, S. kraemeri
Common spotted cuscus, S. maculatus
Waigeou cuscus, S. papuensis
Black-spotted cuscus, S. rufoniger
Blue-eyed spotted cuscus, S. wilsoni
Tribe Trichosurini
Genus Trichosurus
Northern brushtail possum, T. arnhemensis
Short-eared possum, T. caninus
Mountain brushtail possum, T. cunninghami
Coppery brushtail possum, T. johnstonii | Phalangeriformes | Wikipedia | 506 | 46371 | https://en.wikipedia.org/wiki/Phalangeriformes | Biology and health sciences | Diprotodontia | Animals |
Common brushtail possum, T. vulpecula
Genus Wyulda
Scaly-tailed possum, W. squamicaudata
Superfamily Petauroidea
Family Pseudocheiridae: (ring-tailed possums and allies)
Subfamily Hemibelideinae
Genus Hemibelideus
Lemur-like ringtail possum, H. lemuroides
Genus Petauroides
Central greater glider, P. armillatus
Northern greater glider, P. minor
Southern greater glider, P. volans
Subfamily Pseudocheirinae
Genus Petropseudes
Rock-haunting ringtail possum, P. dahli
Genus Pseudocheirus
Common ringtail possum, P. peregrinus
Genus Pseudochirulus
Lowland ringtail possum, P. canescens
Weyland ringtail possum, P. caroli
Cinereus ringtail possum, P. cinereus
Painted ringtail possum, P. forbesi
Herbert River ringtail possum, P. herbertensis
Masked ringtail possum, P. larvatus
Pygmy ringtail possum, P. mayeri
Vogelkop ringtail possum, P. schlegeli
Subfamily Pseudochiropsinae
Genus Pseudochirops
D'Albertis' ringtail possum, P. albertisii
Green ringtail possum, P. archeri
Plush-coated ringtail possum, P. corinnae
Reclusive ringtail possum, P. coronatus
Coppery ringtail possum, P. cupreus
Family Petauridae: (striped possum, Leadbeater's possum, yellow-bellied glider, sugar glider, mahogany glider, squirrel glider)
Genus Dactylopsila
Great-tailed triok, D. megalura
Long-fingered triok, D. palpator
Tate's triok, D. tatei
Striped possum, D. trivirgata
Genus Gymnobelideus
Leadbeater's possum, G. leadbeateri
Genus Petaurus
Northern glider, P. abidi
Savanna glider, P. ariel
Yellow-bellied glider, P. australis
Biak glider, P. biacensis
Sugar glider, P. breviceps
Mahogany glider, P. gracilis
Squirrel glider, P. norfolcensis
Krefft's glider, P. notatus | Phalangeriformes | Wikipedia | 507 | 46371 | https://en.wikipedia.org/wiki/Phalangeriformes | Biology and health sciences | Diprotodontia | Animals |
Family Tarsipedidae: (honey possum)
Genus Tarsipes
Honey possum or noolbenger, T. rostratus
Family Acrobatidae: (feathertail glider and feather-tailed possum)
Genus Acrobates
Feathertail glider, A. pygmaeus
Genus Distoechurus
Feather-tailed possum, D. pennatus | Phalangeriformes | Wikipedia | 81 | 46371 | https://en.wikipedia.org/wiki/Phalangeriformes | Biology and health sciences | Diprotodontia | Animals |
A diatom (Neo-Latin diatoma) is any member of a large group comprising several genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of the Earth's biomass: they generate about 20 to 50 percent of the oxygen produced on the planet each year, take in over 6.7 billion tonnes of silicon each year from the waters in which they live, and constitute nearly half of the organic material found in the oceans. The shells of dead diatoms can reach as much as a half-mile (800 m) deep on the ocean floor, and the entire Amazon basin is fertilized annually by 27 million tons of diatom shell dust transported by transatlantic winds from the African Sahara, much of it from the Bodélé Depression, which was once made up of a system of fresh-water lakes.
Diatoms are unicellular organisms: they occur either as solitary cells or in colonies, which can take the shape of ribbons, fans, zigzags, or stars. Individual cells range in size from 2 to 2000 micrometers. In the presence of adequate nutrients and sunlight, an assemblage of living diatoms doubles approximately every 24 hours by asexual multiple fission; the maximum life span of individual cells is about six days. Diatoms have two distinct shapes: a few (centric diatoms) are radially symmetric, while most (pennate diatoms) are broadly bilaterally symmetric.
The unique feature of diatoms is that they are surrounded by a cell wall made of silica (hydrated silicon dioxide), called a frustule. These frustules produce structural coloration, prompting them to be described as "jewels of the sea" and "living opals".
Movement in diatoms primarily occurs passively as a result of both ocean currents and wind-induced water turbulence; however, male gametes of centric diatoms have flagella, permitting active movement to seek female gametes. Similar to plants, diatoms convert light energy to chemical energy by photosynthesis, but their chloroplasts were acquired in different ways. | Diatom | Wikipedia | 455 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Unusually for autotrophic organisms, diatoms possess a urea cycle, a feature that they share with animals, although this cycle is used to different metabolic ends in diatoms. The family Rhopalodiaceae also possess a cyanobacterial endosymbiont called a spheroid body. This endosymbiont has lost its photosynthetic properties, but has kept its ability to perform nitrogen fixation, allowing the diatom to fix atmospheric nitrogen. Other diatoms in symbiosis with nitrogen-fixing cyanobacteria are among the genera Hemiaulus, Rhizosolenia and Chaetoceros.
Dinotoms are diatoms that have become endosymbionts inside dinoflagellates. Research on the dinoflagellates Durinskia baltica and Glenodinium foliaceum has shown that the endosymbiont event happened so recently, evolutionarily speaking, that their organelles and genome are still intact with minimal to no gene loss. The main difference between these and free living diatoms is that they have lost their cell wall of silica, making them the only known shell-less diatoms.
The study of diatoms is a branch of phycology. Diatoms are classified as eukaryotes, organisms with a nuclear envelope-bound cell nucleus, that separates them from the prokaryotes archaea and bacteria. Diatoms are a type of plankton called phytoplankton, the most common of the plankton types. Diatoms also grow attached to benthic substrates, floating debris, and on macrophytes. They comprise an integral component of the periphyton community. Another classification divides plankton into eight types based on size: in this scheme, diatoms are classed as microalgae. Several systems for classifying the individual diatom species exist.
Fossil evidence suggests that diatoms originated during or before the early Jurassic period, which was about 150 to 200 million years ago. The oldest fossil evidence for diatoms is a specimen of extant genus Hemiaulus in Late Jurassic aged amber from Thailand. | Diatom | Wikipedia | 449 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Diatoms are used to monitor past and present environmental conditions, and are commonly used in studies of water quality. Diatomaceous earth (diatomite) is a collection of diatom shells found in the Earth's crust. They are soft, silica-containing sedimentary rocks which are easily crumbled into a fine powder and typically have a particle size of 10 to 200 μm. Diatomaceous earth is used for a variety of purposes including for water filtration, as a mild abrasive, in cat litter, and as a dynamite stabilizer.
Overview
Diatoms are protists that form massive annual spring and fall blooms in aquatic environments and are estimated to be responsible for about half of photosynthesis in the global oceans. This predictable annual bloom dynamic fuels higher trophic levels and initiates delivery of carbon into the deep ocean biome. Diatoms have complex life history strategies that are presumed to have contributed to their rapid genetic diversification into ~200,000 species that are distributed between the two major diatom groups: centrics and pennates.
Morphology
Diatoms are generally 20 to 200 micrometers in size, with a few larger species. Their yellowish-brown chloroplasts, the site of photosynthesis, are typical of heterokonts, having four cell membranes and containing pigments such as the carotenoid fucoxanthin. Individuals usually lack flagella, but they are present in male gametes of the centric diatoms and have the usual heterokont structure, including the hairs (mastigonemes) characteristic in other groups.
Diatoms are often referred as "jewels of the sea" or "living opals" due to their optical properties. The biological function of this structural coloration is not clear, but it is speculated that it may be related to communication, camouflage, thermal exchange and/or UV protection.
Diatoms build intricate hard but porous cell walls called frustules composed primarily of silica. This siliceous wall can be highly patterned with a variety of pores, ribs, minute spines, marginal ridges and elevations; all of which can be used to delineate genera and species. | Diatom | Wikipedia | 452 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
The cell itself consists of two halves, each containing an essentially flat plate, or valve, and marginal connecting, or girdle band. One half, the hypotheca, is slightly smaller than the other half, the epitheca. Diatom morphology varies. Although the shape of the cell is typically circular, some cells may be triangular, square, or elliptical. Their distinguishing feature is a hard mineral shell or frustule composed of opal (hydrated, polymerized silicic acid).
Diatoms are divided into two groups that are distinguished by the shape of the frustule: the centric diatoms and the pennate diatoms.
Pennate diatoms are bilaterally symmetric. Each one of their valves have openings that are slits along the raphes and their shells are typically elongated parallel to these raphes. They generate cell movement through cytoplasm that streams along the raphes, always moving along solid surfaces.
Centric diatoms are radially symmetric. They are composed of upper and lower valves – epitheca and hypotheca – each consisting of a valve and a girdle band that can easily slide underneath each other and expand to increase cell content over the diatoms progression. The cytoplasm of the centric diatom is located along the inner surface of the shell and provides a hollow lining around the large vacuole located in the center of the cell. This large, central vacuole is filled by a fluid known as "cell sap" which is similar to seawater but varies with specific ion content. The cytoplasmic layer is home to several organelles, like the chloroplasts and mitochondria. Before the centric diatom begins to expand, its nucleus is at the center of one of the valves and begins to move towards the center of the cytoplasmic layer before division is complete. Centric diatoms have a variety of shapes and sizes, depending on from which axis the shell extends, and if spines are present.
Silicification | Diatom | Wikipedia | 422 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Diatom cells are contained within a unique silica cell wall known as a frustule made up of two valves called thecae, that typically overlap one another. The biogenic silica composing the cell wall is synthesised intracellularly by the polymerisation of silicic acid monomers. This material is then extruded to the cell exterior and added to the wall. In most species, when a diatom divides to produce two daughter cells, each cell keeps one of the two-halves and grows a smaller half within it. As a result, after each division cycle, the average size of diatom cells in the population gets smaller. Once such cells reach a certain minimum size, rather than simply divide, they reverse this decline by forming an auxospore, usually through meiosis and sexual reproduction, but exceptions exist. The auxospore expands in size to give rise to a much larger cell, which then returns to size-diminishing divisions. | Diatom | Wikipedia | 196 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
The exact mechanism of transferring silica absorbed by the diatom to the cell wall is unknown. Much of the sequencing of diatom genes comes from the search for the mechanism of silica uptake and deposition in nano-scale patterns in the frustule. The most success in this area has come from two species, Thalassiosira pseudonana, which has become the model species, as the whole genome was sequenced and methods for genetic control were established, and Cylindrotheca fusiformis, in which the important silica deposition proteins silaffins were first discovered. Silaffins, sets of polycationic peptides, were found in C. fusiformis cell walls and can generate intricate silica structures. These structures demonstrated pores of sizes characteristic to diatom patterns. When T. pseudonana underwent genome analysis it was found that it encoded a urea cycle, including a higher number of polyamines than most genomes, as well as three distinct silica transport genes. In a phylogenetic study on silica transport genes from 8 diverse groups of diatoms, silica transport was found to generally group with species. This study also found structural differences between the silica transporters of pennate (bilateral symmetry) and centric (radial symmetry) diatoms. The sequences compared in this study were used to create a diverse background in order to identify residues that differentiate function in the silica deposition process. Additionally, the same study found that a number of the regions were conserved within species, likely the base structure of silica transport. | Diatom | Wikipedia | 322 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
These silica transport proteins are unique to diatoms, with no homologs found in other species, such as sponges or rice. The divergence of these silica transport genes is also indicative of the structure of the protein evolving from two repeated units composed of five membrane bound segments, which indicates either gene duplication or dimerization. The silica deposition that takes place from the membrane bound vesicle in diatoms has been hypothesized to be a result of the activity of silaffins and long chain polyamines. This Silica Deposition Vesicle (SDV) has been characterized as an acidic compartment fused with Golgi-derived vesicles. These two protein structures have been shown to create sheets of patterned silica in-vivo with irregular pores on the scale of diatom frustules. One hypothesis as to how these proteins work to create complex structure is that residues are conserved within the SDV's, which is unfortunately difficult to identify or observe due to the limited number of diverse sequences available. Though the exact mechanism of the highly uniform deposition of silica is as yet unknown, the Thalassiosira pseudonana genes linked to silaffins are being looked to as targets for genetic control of nanoscale silica deposition. | Diatom | Wikipedia | 264 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
The ability of diatoms to make silica-based cell walls has been the subject of fascination for centuries. It started with a microscopic observation by an anonymous English country nobleman in 1703, who observed an object that looked like a chain of regular parallelograms and debated whether it was just crystals of salt, or a plant. The viewer decided that it was a plant because the parallelograms didn't separate upon agitation, nor did they vary in appearance when dried or subjected to warm water (in an attempt to dissolve the "salt"). Unknowingly, the viewer's confusion captured the essence of diatoms—mineral utilizing plants. It is not clear when it was determined that diatom cell walls are made of silica, but in 1939 a seminal reference characterized the material as silicic acid in a "subcolloidal" state Identification of the main chemical component of the cell wall spurred investigations into how it was made. These investigations have involved, and been propelled by, diverse approaches including, microscopy, chemistry, biochemistry, material characterisation, molecular biology, 'omics, and transgenic approaches. The results from this work have given a better understanding of cell wall formation processes, establishing fundamental knowledge which can be used to create models that contextualise current findings and clarify how the process works.
The process of building a mineral-based cell wall inside the cell, then exporting it outside, is a massive event that must involve large numbers of genes and their protein products. The act of building and exocytosing this large structural object in a short time period, synched with cell cycle progression, necessitates substantial physical movements within the cell as well as dedication of a significant proportion of the cell's biosynthetic capacities.
The first characterisations of the biochemical processes and components involved in diatom silicification were made in the late 1990s. These were followed by insights into how higher order assembly of silica structures might occur. More recent reports describe the identification of novel components involved in higher order processes, the dynamics documented through real-time imaging, and the genetic manipulation of silica structure. The approaches established in these recent works provide practical avenues to not only identify the components involved in silica cell wall formation but to elucidate their interactions and spatio-temporal dynamics. This type of holistic understanding will be necessary to achieve a more complete understanding of cell wall synthesis.
Behaviour | Diatom | Wikipedia | 496 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Most centric and araphid pennate diatoms are nonmotile, and their relatively dense cell walls cause them to readily sink. Planktonic forms in open water usually rely on turbulent mixing of the upper layers of the oceanic waters by the wind to keep them suspended in sunlit surface waters. Many planktonic diatoms have also evolved features that slow their sinking rate, such as spines or the ability to grow in colonial chains. These adaptations increase their surface area to volume ratio and drag, allowing them to stay suspended in the water column longer. Individual cells may regulate buoyancy via an ionic pump.
Some pennate diatoms are capable of a type of locomotion called "gliding", which allows them to move across surfaces via adhesive mucilage secreted through a seamlike structure called the raphe. In order for a diatom cell to glide, it must have a solid substrate for the mucilage to adhere to.
Cells are solitary or united into colonies of various kinds, which may be linked by siliceous structures; mucilage pads, stalks or tubes; amorphous masses of mucilage; or by threads of chitin (polysaccharide), which are secreted through strutted processes of the cell.
Life cycle
Reproduction and cell size
Reproduction among these organisms is asexual by binary fission, during which the diatom divides into two parts, producing two "new" diatoms with identical genes. Each new organism receives one of the two frustules – one larger, the other smaller – possessed by the parent, which is now called the epitheca; and is used to construct a second, smaller frustule, the hypotheca. The diatom that received the larger frustule becomes the same size as its parent, but the diatom that received the smaller frustule remains smaller than its parent. This causes the average cell size of this diatom population to decrease. It has been observed, however, that certain taxa have the ability to divide without causing a reduction in cell size. Nonetheless, in order to restore the cell size of a diatom population for those that do endure size reduction, sexual reproduction and auxospore formation must occur. | Diatom | Wikipedia | 456 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Cell division
Vegetative cells of diatoms are diploid (2N) and so meiosis can take place, producing male and female gametes which then fuse to form the zygote. The zygote sheds its silica theca and grows into a large sphere covered by an organic membrane, the auxospore. A new diatom cell of maximum size, the initial cell, forms within the auxospore thus beginning a new generation. Resting spores may also be formed as a response to unfavourable environmental conditions with germination occurring when conditions improve.
A defining characteristic of all diatoms is their restrictive and bipartite silica cell wall that causes them to progressively shrink during asexual cell division. At a critically small cell size and under certain conditions, auxosporulation restitutes cell size and prevents clonal death. The entire lifecycles of only a few diatoms have been described and rarely have sexual events been captured in the environment.
Sexual reproduction
Most eukaryotes are capable of sexual reproduction involving meiosis. Sexual reproduction appears to be an obligatory phase in the life cycle of diatoms, particularly as cell size decreases with successive vegetative divisions. Sexual reproduction involves production of gametes and the fusion of gametes to form a zygote in which maximal cell size is restored. The signaling that triggers the sexual phase is favored when cells accumulate together, so that the distance between them is reduced and the contacts and/or the perception of chemical cues is facilitated.
An exploration of the genomes of five diatoms and one diatom transcriptome led to the identification of 42 genes potentially involved in meiosis. Thus a meiotic toolkit appears to be conserved in these six diatom species, indicating a central role of meiosis in diatoms as in other eukaryotes. | Diatom | Wikipedia | 380 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Sperm motility
Diatoms are mostly non-motile; however, sperm found in some species can be flagellated, though motility is usually limited to a gliding motion. In centric diatoms, the small male gametes have one flagellum while the female gametes are large and non-motile (oogamous). Conversely, in pennate diatoms both gametes lack flagella (isogamous). Certain araphid species, that is pennate diatoms without a raphe (seam), have been documented as anisogamous and are, therefore, considered to represent a transitional stage between centric and raphid pennate diatoms, diatoms with a raphe.
Degradation by microbes
Certain species of bacteria in oceans and lakes can accelerate the rate of dissolution of silica in dead and living diatoms by using hydrolytic enzymes to break down the organic algal material.
Ecology
Distribution
Diatoms are a widespread group and can be found in the oceans, in fresh water, in soils, and on damp surfaces. They are one of the dominant components of phytoplankton in nutrient-rich coastal waters and during oceanic spring blooms, since they can divide more rapidly than other groups of phytoplankton. Most live pelagically in open water, although some live as surface films at the water-sediment interface (benthic), or even under damp atmospheric conditions. They are especially important in oceans, where a 2003 study found that they contribute an estimated 45% of the total oceanic primary production of organic material. However, a more recent 2016 study estimates that the number is closer to 20%. Spatial distribution of marine phytoplankton species is restricted both horizontally and vertically.
Growth
Planktonic diatoms in freshwater and marine environments typically exhibit a "boom and bust" (or "bloom and bust") lifestyle. When conditions in the upper mixed layer (nutrients and light) are favourable (as at the spring), their competitive edge and rapid growth rate enables them to dominate phytoplankton communities ("boom" or "bloom"). As such they are often classed as opportunistic r-strategists (i.e. those organisms whose ecology is defined by a high growth rate, r). | Diatom | Wikipedia | 479 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Impact
The freshwater diatom Didymosphenia geminata, commonly known as Didymo, causes severe environmental degradation in water-courses where it blooms, producing large quantities of a brown jelly-like material called "brown snot" or "rock snot". This diatom is native to Europe and is an invasive species both in the antipodes and in parts of North America. The problem is most frequently recorded from Australia and New Zealand.
When conditions turn unfavourable, usually upon depletion of nutrients, diatom cells typically increase in sinking rate and exit the upper mixed layer ("bust"). This sinking is induced by either a loss of buoyancy control, the synthesis of mucilage that sticks diatoms cells together, or the production of heavy resting spores. Sinking out of the upper mixed layer removes diatoms from conditions unfavourable to growth, including grazer populations and higher temperatures (which would otherwise increase cell metabolism). Cells reaching deeper water or the shallow seafloor can then rest until conditions become more favourable again. In the open ocean, many sinking cells are lost to the deep, but refuge populations can persist near the thermocline.
Ultimately, diatom cells in these resting populations re-enter the upper mixed layer when vertical mixing entrains them. In most circumstances, this mixing also replenishes nutrients in the upper mixed layer, setting the scene for the next round of diatom blooms. In the open ocean (away from areas of continuous upwelling), this cycle of bloom, bust, then return to pre-bloom conditions typically occurs over an annual cycle, with diatoms only being prevalent during the spring and early summer. In some locations, however, an autumn bloom may occur, caused by the breakdown of summer stratification and the entrainment of nutrients while light levels are still sufficient for growth. Since vertical mixing is increasing, and light levels are falling as winter approaches, these blooms are smaller and shorter-lived than their spring equivalents.
In the open ocean, the diatom (spring) bloom is typically ended by a shortage of silicon. Unlike other minerals, the requirement for silicon is unique to diatoms and it is not regenerated in the plankton ecosystem as efficiently as, for instance, nitrogen or phosphorus nutrients. This can be seen in maps of surface nutrient concentrations – as nutrients decline along gradients, silicon is usually the first to be exhausted (followed normally by nitrogen then phosphorus). | Diatom | Wikipedia | 511 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Because of this bloom-and-bust cycle, diatoms are believed to play a disproportionately important role in the export of carbon from oceanic surface waters (see also the biological pump). Significantly, they also play a key role in the regulation of the biogeochemical cycle of silicon in the modern ocean.
Reason for success
Diatoms are ecologically successful, and occur in virtually every environment that contains water – not only oceans, seas, lakes, and streams, but also soil and wetlands. The use of silicon by diatoms is believed by many researchers to be the key to this ecological success. Raven (1983) noted that, relative to organic cell walls, silica frustules require less energy to synthesize (approximately 8% of a comparable organic wall), potentially a significant saving on the overall cell energy budget. In a now classic study, Egge and Aksnes (1992) found that diatom dominance of mesocosm communities was directly related to the availability of silicic acid – when concentrations were greater than 2 μmol m−3, they found that diatoms typically represented more than 70% of the phytoplankton community. Other researchers have suggested that the biogenic silica in diatom cell walls acts as an effective pH buffering agent, facilitating the conversion of bicarbonate to dissolved CO2 (which is more readily assimilated). More generally, notwithstanding these possible advantages conferred by their use of silicon, diatoms typically have higher growth rates than other algae of the same corresponding size.
Sources for collection | Diatom | Wikipedia | 328 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Diatoms can be obtained from multiple sources. Marine diatoms can be collected by direct water sampling, and benthic forms can be secured by scraping barnacles, oyster and other shells. Diatoms are frequently present as a brown, slippery coating on submerged stones and sticks, and may be seen to "stream" with river current. The surface mud of a pond, ditch, or lagoon will almost always yield some diatoms. Living diatoms are often found clinging in great numbers to filamentous algae, or forming gelatinous masses on various submerged plants. Cladophora is frequently covered with Cocconeis, an elliptically shaped diatom; Vaucheria is often covered with small forms. Since diatoms form an important part of the food of molluscs, tunicates, and fishes, the alimentary tracts of these animals often yield forms that are not easily secured in other ways. Diatoms can be made to emerge by filling a jar with water and mud, wrapping it in black paper and letting direct sunlight fall on the surface of the water. Within a day, the diatoms will come to the top in a scum and can be isolated.
Biogeochemistry
Silica cycle
The diagram shows the major fluxes of silicon in the current ocean. Most biogenic silica in the ocean (silica produced by biological activity) comes from diatoms. Diatoms extract dissolved silicic acid from surface waters as they grow, and return it to the water column when they die. Inputs of silicon arrive from above via aeolian dust, from the coasts via rivers, and from below via seafloor sediment recycling, weathering, and hydrothermal activity.
Although diatoms may have existed since the Triassic, the timing of their ascendancy and "take-over" of the silicon cycle occurred more recently. Prior to the Phanerozoic (before 544 Ma), it is believed that microbial or inorganic processes weakly regulated the ocean's silicon cycle. Subsequently, the cycle appears dominated (and more strongly regulated) by the radiolarians and siliceous sponges, the former as zooplankton, the latter as sedentary filter-feeders primarily on the continental shelves. Within the last 100 My, it is thought that the silicon cycle has come under even tighter control, and that this derives from the ecological ascendancy of the diatoms. | Diatom | Wikipedia | 503 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
However, the precise timing of the "take-over" remains unclear, and different authors have conflicting interpretations of the fossil record. Some evidence, such as the displacement of siliceous sponges from the shelves, suggests that this takeover began in the Cretaceous (146 Ma to 66 Ma), while evidence from radiolarians suggests "take-over" did not begin until the Cenozoic (66 Ma to present).
Carbon cycle
The diagram depicts some mechanisms by which marine diatoms contribute to the biological carbon pump and influence the ocean carbon cycle. The anthropogenic CO2 emission to the atmosphere (mainly generated by fossil fuel burning and deforestation) is nearly 11 gigatonne carbon (GtC) per year, of which almost 2.5 GtC is taken up by the surface ocean. In surface seawater (pH 8.1–8.4), bicarbonate () and carbonate ions () constitute nearly 90 and <10% of dissolved inorganic carbon (DIC) respectively, while dissolved CO2 (CO2 aqueous) contributes <1%. Despite this low level of CO2 in the ocean and its slow diffusion rate in water, diatoms fix 10–20 GtC annually via photosynthesis thanks to their carbon dioxide concentrating mechanisms, allowing them to sustain marine food chains. In addition, 0.1–1% of this organic material produced in the euphotic layer sinks down as particles, thus transferring the surface carbon toward the deep ocean and sequestering atmospheric CO2 for thousands of years or longer. The remaining organic matter is remineralized through respiration. Thus, diatoms are one of the main players in this biological carbon pump, which is arguably the most important biological mechanism in the Earth System allowing CO2 to be removed from the carbon cycle for very long period.
Urea cycle
A feature of diatoms is the urea cycle, which links them evolutionarily to animals. In 2011, Allen et al. established that diatoms have a functioning urea cycle. This result was significant, since prior to this, the urea cycle was thought to have originated with the metazoans which appeared several hundreds of millions of years before the diatoms. Their study demonstrated that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionarily linked in such a way that animals and plants are not. | Diatom | Wikipedia | 496 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
While often overlooked in photosynthetic organisms, the mitochondria also play critical roles in energy balance. Two nitrogen-related pathways are relevant and they may also change under ammonium () nutrition compared with nitrate () nutrition. First, in diatoms, and likely some other algae, there is a urea cycle. The long-known function of the urea cycle in animals is to excrete excess nitrogen produced by amino acid Catabolism; like photorespiration, the urea cycle had long been considered a waste pathway. However, in diatoms the urea cycle appears to play a role in exchange of nutrients between the mitochondria and the cytoplasm, and potentially the plastid and may help to regulate ammonium metabolism. Because of this cycle, marine diatoms, in contrast to chlorophytes, also have acquired a mitochondrial urea transporter and, in fact, based on bioinformatics, a complete mitochondrial GS-GOGAT cycle has been hypothesised.
Other
Diatoms are mainly photosynthetic; however a few are obligate heterotrophs and can live in the absence of light provided an appropriate organic carbon source is available.
Photosynthetic diatoms that find themselves in an environment absent of oxygen and/or sunlight can switch to anaerobic respiration known as nitrate respiration (DNRA), and stay dormant for up till months and decades.
Major pigments of diatoms are chlorophylls a and c, beta-carotene, fucoxanthin, diatoxanthin and diadinoxanthin.
Taxonomy | Diatom | Wikipedia | 343 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Diatoms belong to a large group of protists, many of which contain plastids rich in chlorophylls a and c. The group has been variously referred to as heterokonts, chrysophytes, chromists or stramenopiles. Many are autotrophs such as golden algae and kelp; and heterotrophs such as water moulds, opalinids, and actinophryid heliozoa. The classification of this area of protists is still unsettled. In terms of rank, they have been treated as a division, phylum, kingdom, or something intermediate to those. Consequently, diatoms are ranked anywhere from a class, usually called Diatomophyceae or Bacillariophyceae, to a division (=phylum), usually called Bacillariophyta, with corresponding changes in the ranks of their subgroups.
Genera and species
An estimated 20,000 extant diatom species are believed to exist, of which around 12,000 have been named to date according to Guiry, 2012 (other sources give a wider range of estimates). Around 1,000–1,300 diatom genera have been described, both extant and fossil, of which some 250–300 exist only as fossils.
Classes and orders
For many years the diatoms—treated either as a class (Bacillariophyceae) or a phylum (Bacillariophyta)—were divided into just 2 orders, corresponding to the centric and the pennate diatoms (Centrales and Pennales). This classification was extensively overhauled by Round, Crawford and Mann in 1990 who treated the diatoms at a higher rank (division, corresponding to phylum in zoological classification), and promoted the major classification units to classes, maintaining the centric diatoms as a single class Coscinodiscophyceae, but splitting the former pennate diatoms into 2 separate classes, Fragilariophyceae and Bacillariophyceae (the latter older name retained but with an emended definition), between them encompassing 45 orders, the majority of them new. | Diatom | Wikipedia | 456 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Today (writing at mid 2020) it is recognised that the 1990 system of Round et al. is in need of revision with the advent of newer molecular work, however the best system to replace it is unclear, and current systems in widespread use such as AlgaeBase, the World Register of Marine Species and its contributing database DiatomBase, and the system for "all life" represented in Ruggiero et al., 2015, all retain the Round et al. treatment as their basis, albeit with diatoms as a whole treated as a class rather than division/phylum, and Round et al.'s classes reduced to subclasses, for better agreement with the treatment of phylogenetically adjacent groups and their containing taxa. (For references refer the individual sections below). | Diatom | Wikipedia | 158 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
One proposal, by Linda Medlin and co-workers commencing in 2004, is for some of the centric diatom orders considered more closely related to the pennates to be split off as a new class, Mediophyceae, itself more closely aligned with the pennate diatoms than the remaining centrics. This hypothesis—later designated the Coscinodiscophyceae-Mediophyceae-Bacillariophyceae, or Coscinodiscophyceae+(Mediophyceae+Bacillariophyceae) (CMB) hypothesis—has been accepted by D.G. Mann among others, who uses it as the basis for the classification of diatoms as presented in Adl. et al.'s series of syntheses (2005, 2012, 2019), and also in the Bacillariophyta chapter of the 2017 Handbook of the Protists edited by Archibald et al., with some modifications reflecting the apparent non-monophyly of Medlin et al. original "Coscinodiscophyceae". Meanwhile, a group led by E.C. Theriot favours a different hypothesis of phylogeny, which has been termed the structural gradation hypothesis (SGH) and does not recognise the Mediophyceae as a monophyletic group, while another analysis, that of Parks et al., 2018, finds that the radial centric diatoms (Medlin et al.'s Coscinodiscophyceae) are not monophyletic, but supports the monophyly of Mediophyceae minus Attheya, which is an anomalous genus. Discussion of the relative merits of these conflicting schemes continues by the various parties involved. | Diatom | Wikipedia | 362 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Adl et al., 2019 treatment
In 2019, Adl et al. presented the following classification of diatoms, while noting: "This revision reflects numerous advances in the phylogeny of the diatoms over the last decade. Due to our poor taxon sampling outside of the Mediophyceae and pennate diatoms, and the known and anticipated diversity of all diatoms, many clades appear at a high classification level (and the higher level classification is rather flat)." This classification treats diatoms as a phylum (Diatomeae/Bacillariophyta), accepts the class Mediophyceae of Medlin and co-workers, introduces new subphyla and classes for a number of otherwise isolated genera, and re-ranks a number of previously established taxa as subclasses, but does not list orders or families. Inferred ranks have been added for clarity (Adl. et al. do not use ranks, but the intended ones in this portion of the classification are apparent from the choice of endings used, within the system of botanical nomenclature employed).
Clade Diatomista Derelle et al. 2016, emend. Cavalier-Smith 2017 (diatoms plus a subset of other ochrophyte groups)
Phylum Diatomeae Dumortier 1821 [= Bacillariophyta Haeckel 1878] (diatoms)
Subphylum Leptocylindrophytina D.G. Mann in Adl et al. 2019
Class Leptocylindrophyceae D.G. Mann in Adl et al. 2019 (Leptocylindrus, Tenuicylindrus)
Class Corethrophyceae D.G. Mann in Adl et al. 2019 (Corethron)
Subphylum Ellerbeckiophytina D.G. Mann in Adl et al. 2019 (Ellerbeckia)
Subphylum Probosciophytina D.G. Mann in Adl et al. 2019 (Proboscia)
Subphylum Melosirophytina D.G. Mann in Adl et al. 2019 (Aulacoseira, Melosira, Hyalodiscus, Stephanopyxis, Paralia, Endictya) | Diatom | Wikipedia | 474 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Subphylum Coscinodiscophytina Medlin & Kaczmarska 2004, emend. (Actinoptychus, Coscinodiscus, Actinocyclus, Asteromphalus, Aulacodiscus, Stellarima)
Subphylum Rhizosoleniophytina D.G. Mann in Adl et al. 2019 (Guinardia, Rhizosolenia, Pseudosolenia)
Subphylum Arachnoidiscophytina D.G. Mann in Adl et al. 2019 (Arachnoidiscus)
Subphylum Bacillariophytina Medlin & Kaczmarska 2004, emend.
Class Mediophyceae Jouse & Proshkina-Lavrenko in Medlin & Kaczmarska 2004
Subclass Chaetocerotophycidae Round & R.M. Crawford in Round et al. 1990, emend.
Subclass Lithodesmiophycidae Round & R.M. Crawford in Round et al. 1990, emend.
Subclass Thalassiosirophycidae Round & R.M. Crawford in Round et al. 1990
Subclass Cymatosirophycidae Round & R.M. Crawford in Round et al. 1990
Subclass Odontellophycidae D.G. Mann in Adl et al. 2019
Subclass Chrysanthemodiscophycidae D.G. Mann in Adl et al. 2019
Class Biddulphiophyceae D.G. Mann in Adl et al. 2019
Subclass Biddulphiophycidae Round and R.M. Crawford in Round et al. 1990, emend.
Biddulphiophyceae incertae sedis (Attheya)
Class Bacillariophyceae Haeckel 1878, emend.
Bacillariophyceae incertae sedis (Striatellaceae)
Subclass Urneidophycidae Medlin 2016
Subclass Fragilariophycidae Round in Round, Crawford & Mann 1990, emend.
Subclass Bacillariophycidae D.G. Mann in Round, Crawford & Mann 1990, emend. | Diatom | Wikipedia | 463 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
See taxonomy of diatoms for more details.
Gallery
Three diatom species were sent to the International Space Station, including the huge (6 mm length) diatoms of Antarctica and the exclusive colonial diatom, Bacillaria paradoxa. The cells of Bacillaria moved next to each other in partial but opposite synchrony by a microfluidics method.
Evolution and fossil record
Origin
Heterokont chloroplasts appear to derive from those of red algae, rather than directly from prokaryotes as occurred in plants. This suggests they had a more recent origin than many other algae. However, fossil evidence is scant, and only with the evolution of the diatoms themselves do the heterokonts make a serious impression on the fossil record.
Earliest fossils
The earliest known fossil diatoms date from the early Jurassic (~185 Ma ago), although the molecular clock and sedimentary evidence suggests an earlier origin. It has been suggested that their origin may be related to the end-Permian mass extinction (~250 Ma), after which many marine niches were opened. The gap between this event and the time that fossil diatoms first appear may indicate a period when diatoms were unsilicified and their evolution was cryptic. Since the advent of silicification, diatoms have made a significant impression on the fossil record, with major fossil deposits found as far back as the early Cretaceous, and with some rocks such as diatomaceous earth, being composed almost entirely of them.
Relation to grasslands
The expansion of grassland biomes and the evolutionary radiation of grasses during the Miocene is believed to have increased the flux of soluble silicon to the oceans, and it has been argued that this promoted the diatoms during the Cenozoic era. Recent work suggests that diatom success is decoupled from the evolution of grasses, although both diatom and grassland diversity increased strongly from the middle Miocene.
Relation to climate
Diatom diversity over the Cenozoic has been very sensitive to global temperature, particularly to the equator-pole temperature gradient. Warmer oceans, particularly warmer polar regions, have in the past been shown to have had substantially lower diatom diversity. Future warm oceans with enhanced polar warming, as projected in global-warming scenarios, could thus in theory result in a significant loss of diatom diversity, although from current knowledge it is impossible to say if this would occur rapidly or only over many tens of thousands of years. | Diatom | Wikipedia | 501 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Method of investigation
The fossil record of diatoms has largely been established through the recovery of their siliceous frustules in marine and non-marine sediments. Although diatoms have both a marine and non-marine stratigraphic record, diatom biostratigraphy, which is based on time-constrained evolutionary originations and extinctions of unique taxa, is only well developed and widely applicable in marine systems. The duration of diatom species ranges have been documented through the study of ocean cores and rock sequences exposed on land. Where diatom biozones are well established and calibrated to the geomagnetic polarity time scale (e.g., Southern Ocean, North Pacific, eastern equatorial Pacific), diatom-based age estimates may be resolved to within <100,000 years, although typical age resolution for Cenozoic diatom assemblages is several hundred thousand years.
Diatoms preserved in lake sediments are widely used for paleoenvironmental reconstructions of Quaternary climate, especially for closed-basin lakes which experience fluctuations in water depth and salinity.
Isotope records
When diatoms die their shells (frustules) can settle on the seafloor and become microfossils. Over time, these microfossils become buried as opal deposits in the marine sediment. Paleoclimatology is the study of past climates. Proxy data is used in order to relate elements collected in modern-day sedimentary samples to climatic and oceanic conditions in the past. Paleoclimate proxies refer to preserved or fossilized physical markers which serve as substitutes for direct meteorological or ocean measurements. An example of proxies is the use of diatom isotope records of δ13C, δ18O, δ30Si (δ13Cdiatom, δ18Odiatom, and δ30Sidiatom). In 2015, Swann and Snelling used these isotope records to document historic changes in the photic zone conditions of the north-west Pacific Ocean, including nutrient supply and the efficiency of the soft-tissue biological pump, from the modern day back to marine isotope stage 5e, which coincides with the last interglacial period. Peaks in opal productivity in the marine isotope stage are associated with the breakdown of the regional halocline stratification and increased nutrient supply to the photic zone. | Diatom | Wikipedia | 489 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
The initial development of the halocline and stratified water column has been attributed to the onset of major Northern Hemisphere glaciation at 2.73 Ma, which increased the flux of freshwater to the region, via increased monsoonal rainfall and/or glacial meltwater, and sea surface temperatures. The decrease of abyssal water upwelling associated with this may have contributed to the establishment of globally cooler conditions and the expansion of glaciers across the Northern Hemisphere from 2.73 Ma. While the halocline appears to have prevailed through the late Pliocene and early Quaternary glacial–interglacial cycles, other studies have shown that the stratification boundary may have broken down in the late Quaternary at glacial terminations and during the early part of interglacials.
Diversification
The Cretaceous record of diatoms is limited, but recent studies reveal a progressive diversification of diatom types. The Cretaceous–Paleogene extinction event, which in the oceans dramatically affected organisms with calcareous skeletons, appears to have had relatively little impact on diatom evolution.
Turnover
Although no mass extinctions of marine diatoms have been observed during the Cenozoic, times of relatively rapid evolutionary turnover in marine diatom species assemblages occurred near the Paleocene–Eocene boundary, and at the Eocene–Oligocene boundary. Further turnover of assemblages took place at various times between the middle Miocene and late Pliocene, in response to progressive cooling of polar regions and the development of more endemic diatom assemblages.
A global trend toward more delicate diatom frustules has been noted from the Oligocene to the Quaternary. This coincides with an increasingly more vigorous circulation of the ocean's surface and deep waters brought about by increasing latitudinal thermal gradients at the onset of major ice sheet expansion on Antarctica and progressive cooling through the Neogene and Quaternary towards a bipolar glaciated world. This caused diatoms to take in less silica for the formation of their frustules. Increased mixing of the oceans renews silica and other nutrients necessary for diatom growth in surface waters, especially in regions of coastal and oceanic upwelling.
Genetics | Diatom | Wikipedia | 458 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Expressed sequence tagging
In 2002, the first insights into the properties of the Phaeodactylum tricornutum gene repertoire were described using 1,000 expressed sequence tags (ESTs). Subsequently, the number of ESTs was extended to 12,000 and the diatom EST database was constructed for functional analyses. These sequences have been used to make a comparative analysis between P. tricornutum and the putative complete proteomes from the green alga Chlamydomonas reinhardtii, the red alga Cyanidioschyzon merolae, and the diatom Thalassiosira pseudonana. The diatom EST database now consists of over 200,000 ESTs from P. tricornutum (16 libraries) and T. pseudonana (7 libraries) cells grown in a range of different conditions, many of which correspond to different abiotic stresses.
Genome sequencing
In 2004, the entire genome of the centric diatom, Thalassiosira pseudonana (32.4 Mb) was sequenced, followed in 2008 with the sequencing of the pennate diatom, Phaeodactylum tricornutum (27.4 Mb). Comparisons of the two reveal that the P. tricornutum genome includes fewer genes (10,402 opposed to 11,776) than T. pseudonana; no major synteny (gene order) could be detected between the two genomes. T. pseudonana genes show an average of ~1.52 introns per gene as opposed to 0.79 in P. tricornutum, suggesting recent widespread intron gain in the centric diatom. Despite relatively recent evolutionary divergence (90 million years), the extent of molecular divergence between centrics and pennates indicates rapid evolutionary rates within the Bacillariophyceae compared to other eukaryotic groups. Comparative genomics also established that a specific class of transposable elements, the Diatom Copia-like retrotransposons (or CoDis), has been significantly amplified in the P. tricornutum genome with respect to T. pseudonana, constituting 5.8 and 1% of the respective genomes. | Diatom | Wikipedia | 462 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Endosymbiotic gene transfer
Diatom genomics brought much information about the extent and dynamics of the endosymbiotic gene transfer (EGT) process. Comparison of the T. pseudonana proteins with homologs in other organisms suggested that hundreds have their closest homologs in the Plantae lineage. EGT towards diatom genomes can be illustrated by the fact that the T. pseudonana genome encodes six proteins which are most closely related to genes encoded by the Guillardia theta (cryptomonad) nucleomorph genome. Four of these genes are also found in red algal plastid genomes, thus demonstrating successive EGT from red algal plastid to red algal nucleus (nucleomorph) to heterokont host nucleus. More recent phylogenomic analyses of diatom proteomes provided evidence for a prasinophyte-like endosymbiont in the common ancestor of chromalveolates as supported by the fact the 70% of diatom genes of Plantae origin are of green lineage provenance and that such genes are also found in the genome of other stramenopiles. Therefore, it was proposed that chromalveolates are the product of serial secondary endosymbiosis first with a green algae, followed by a second one with a red algae that conserved the genomic footprints of the previous but displaced the green plastid. However, phylogenomic analyses of diatom proteomes and chromalveolate evolutionary history will likely take advantage of complementary genomic data from under-sequenced lineages such as red algae.
Horizontal gene transfer
In addition to EGT, horizontal gene transfer (HGT) can occur independently of an endosymbiotic event. The publication of the P. tricornutum genome reported that at least 587 P. tricornutum genes appear to be most closely related to bacterial genes, accounting for more than 5% of the P. tricornutum proteome. About half of these are also found in the T. pseudonana genome, attesting their ancient incorporation in the diatom lineage. | Diatom | Wikipedia | 449 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Genetic engineering
To understand the biological mechanisms which underlie the great importance of diatoms in geochemical cycles, scientists have used the Phaeodactylum tricornutum and Thalassiosira spp. species as model organisms since the 90's.
Few molecular biology tools are currently available to generate mutants or transgenic lines : plasmids containing transgenes are inserted into the cells using the biolistic method or transkingdom bacterial conjugation (with 10−6 and 10−4 yield respectively), and other classical transfection methods such as electroporation or use of PEG have been reported to provide results with lower efficiencies.
Transfected plasmids can be either randomly integrated into the diatom's chromosomes or maintained as stable circular episomes (thanks to the CEN6-ARSH4-HIS3 yeast centromeric sequence). The phleomycin/zeocin resistance gene Sh Ble is commonly used as a selection marker, and various transgenes have been successfully introduced and expressed in diatoms with stable transmissions through generations, or with the possibility to remove it.
Furthermore, these systems now allow the use of the CRISPR-Cas genome edition tool, leading to a fast production of functional knock-out mutants and a more accurate comprehension of the diatoms' cellular processes.
Human uses
Paleontology
Decomposition and decay of diatoms leads to organic and inorganic (in the form of silicates) sediment, the inorganic component of which can lead to a method of analyzing past marine environments by corings of ocean floors or bay muds, since the inorganic matter is embedded in deposition of clays and silts and forms a permanent geological record of such marine strata (see siliceous ooze).
Industrial
Diatoms, and their shells (frustules) as diatomite or diatomaceous earth, are important industrial resources used for fine polishing and liquid filtration. The complex structure of their microscopic shells has been proposed as a material for nanotechnology. | Diatom | Wikipedia | 422 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Diatomite is considered to be a natural nano material and has many uses and applications such as: production of various ceramic products, construction ceramics, refractory ceramics, special oxide ceramics, for production of humidity control materials, used as filtration material, material in the cement production industry, initial material for production of prolonged-release drug carriers, absorption material in an industrial scale, production of porous ceramics, glass industry, used as catalyst support, as a filler in plastics and paints, purification of industrial waters, pesticide holder, as well as for improving the physical and chemical characteristics of certain soils, and other uses.
Diatoms are also used to help determine the origin of materials containing them, including seawater.
Nanotechnology
The deposition of silica by diatoms may also prove to be of utility to nanotechnology. Diatom cells repeatedly and reliably manufacture valves of various shapes and sizes, potentially allowing diatoms to manufacture micro- or nano-scale structures which may be of use in a range of devices, including: optical systems; semiconductor nanolithography; and even vehicles for drug delivery. With an appropriate artificial selection procedure, diatoms that produce valves of particular shapes and sizes might be evolved for cultivation in chemostat cultures to mass-produce nanoscale components. It has also been proposed that diatoms could be used as a component of solar cells by substituting photosensitive titanium dioxide for the silicon dioxide that diatoms normally use to create their cell walls. Diatom biofuel producing solar panels have also been proposed.
Forensic
The main goal of diatom analysis in forensics is to differentiate a death by submersion from a post-mortem immersion of a body in water. Laboratory tests may reveal the presence of diatoms in the body. Since the silica-based skeletons of diatoms do not readily decay, they can sometimes be detected even in heavily decomposed bodies. As they do not occur naturally in the body, if laboratory tests show diatoms in the corpse that are of the same species found in the water where the body was recovered, then it may be good evidence of drowning as the cause of death. The blend of diatom species found in a corpse may be the same or different from the surrounding water, indicating whether the victim drowned in the same site in which the body was found.
History of discovery | Diatom | Wikipedia | 488 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
The first illustrations of diatoms are found in an article from 1703 in Transactions of the Royal Society showing unmistakable drawings of Tabellaria. Although the publication was authored by an unnamed English gentleman, there is recent evidence that he was Charles King of Staffordshire. The first formally identified diatom, the colonial Bacillaria paxillifera, was discovered and described in 1783 by Danish naturalist Otto Friedrich Müller. Like many others after him, he wrongly thought that it was an animal due to its ability to move. Even Charles Darwin saw diatom remains in dust whilst in the Cape Verde Islands, although he was not sure what they were. It was only later that they were identified for him as siliceous polygastrics. The infusoria that Darwin later noted in the face paint of Fueguinos, native inhabitants of Tierra del Fuego in the southern end of South America, were later identified in the same way. During his lifetime, the siliceous polygastrics were clarified as belonging to the Diatomaceae, and Darwin struggled to understand the reasons underpinning their beauty. He exchanged opinions with the noted cryptogamist G. H. K. Thwaites on the topic. In the fourth edition of On the Origin of Species, he wrote, "Few objects are more beautiful than the minute siliceous cases of the diatomaceae: were these created that they might be examined and admired under the high powers of the microscope?" and reasoned that their exquisite morphologies must have functional underpinnings rather than having been created purely for humans to admire. | Diatom | Wikipedia | 322 | 46374 | https://en.wikipedia.org/wiki/Diatom | Biology and health sciences | Other organisms | null |
Coaxial cable, or coax (pronounced ), is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric (insulating material); many coaxial cables also have a protective outer sheath or jacket. The term coaxial refers to the inner conductor and the outer shield sharing a geometric axis.
Coaxial cable is a type of transmission line, used to carry high-frequency electrical signals with low losses. It is used in such applications as telephone trunk lines, broadband internet networking cables, high-speed computer data busses, cable television signals, and connecting radio transmitters and receivers to their antennas. It differs from other shielded cables because the dimensions of the cable and connectors are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a transmission line.
Coaxial cable was used in the first (1858) and following transatlantic cable installations, but its theory was not described until 1880 by English physicist, engineer, and mathematician Oliver Heaviside, who patented the design in that year (British patent No. 1,407).
Applications
Coaxial cable is used as a transmission line for radio frequency signals. Its applications include feedlines connecting radio transmitters and receivers to their antennas, computer network (e.g., Ethernet) connections, digital audio (S/PDIF), and distribution of cable television signals. One advantage of coaxial over other types of radio transmission line is that in an ideal coaxial cable the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors. This allows coaxial cable runs to be installed next to metal objects such as gutters without the power losses that occur in other types of transmission lines. Coaxial cable also provides protection of the signal from external electromagnetic interference.
Description | Coaxial cable | Wikipedia | 381 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Coaxial cable conducts electrical signals using an inner conductor (usually a solid copper, stranded copper or copper-plated steel wire) surrounded by an insulating layer and all enclosed by a shield, typically one to four layers of woven metallic braid and metallic tape. The cable is protected by an outer insulating jacket. Normally, the outside of the shield is kept at ground potential and a signal carrying voltage is applied to the center conductor. When using differential signaling, coaxial cable provides an advantage of equal push-pull currents on the inner conductor and inside of the outer conductor that restrict the signal's electric and magnetic fields to the dielectric, with little leakage outside the shield. Further, electric and magnetic fields outside the cable are largely kept from interfering with signals inside the cable, if unequal currents are filtered out at the receiving end of the line. This property makes coaxial cable a good choice both for carrying weak signals that cannot tolerate interference from the environment, and for stronger electrical signals that must not be allowed to radiate or couple into adjacent structures or circuits. Larger diameter cables and cables with multiple shields have less leakage.
Common applications of coaxial cable include video and CATV distribution, RF and microwave transmission, and computer and instrumentation data connections.
The characteristic impedance of the cable () is determined by the dielectric constant of the inner insulator and the radii of the inner and outer conductors. In radio frequency systems, where the cable length is comparable to the wavelength of the signals transmitted, a uniform cable characteristic impedance is important to minimize loss. The source and load impedances are chosen to match the impedance of the cable to ensure maximum power transfer and minimum standing wave ratio. Other important properties of coaxial cable include attenuation as a function of frequency, voltage handling capability, and shield quality.
Construction
Coaxial cable design choices affect physical size, frequency performance, attenuation, power handling capabilities, flexibility, strength, and cost. The inner conductor might be solid or stranded; stranded is more flexible. To get better high-frequency performance, the inner conductor may be silver-plated. Copper-plated steel wire is often used as an inner conductor for cable used in the cable TV industry. | Coaxial cable | Wikipedia | 461 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
The insulator surrounding the inner conductor may be solid plastic, a foam plastic, or air with spacers supporting the inner wire. The properties of the dielectric insulator determine some of the electrical properties of the cable. A common choice is a solid polyethylene (PE) insulator, used in lower-loss cables. Solid Teflon (PTFE) is also used as an insulator, and exclusively in plenum-rated cables. Some coaxial lines use air (or some other gas) and have spacers to keep the inner conductor from touching the shield.
Many conventional coaxial cables use braided copper wire forming the shield. This allows the cable to be flexible, but it also means there are gaps in the shield layer, and the inner dimension of the shield varies slightly because the braid cannot be flat. Sometimes the braid is silver-plated. For better shield performance, some cables have a double-layer shield. The shield might be just two braids, but it is more common now to have a thin foil shield covered by a wire braid. Some cables may invest in more than two shield layers, such as "quad-shield", which uses four alternating layers of foil and braid. Other shield designs sacrifice flexibility for better performance; some shields are a solid metal tube. Those cables cannot be bent sharply, as the shield will kink, causing losses in the cable. When a foil shield is used a small wire conductor incorporated into the foil makes soldering the shield termination easier.
For high-power radio-frequency transmission up to about 1 GHz, coaxial cable with a solid copper outer conductor is available in sizes of 0.25 inch upward. The outer conductor is corrugated like a bellows to permit flexibility and the inner conductor is held in position by a plastic spiral to approximate an air dielectric. One brand name for such cable is Heliax.
Coaxial cables require an internal structure of an insulating (dielectric) material to maintain the spacing between the center conductor and shield. The dielectric losses increase in this order: Ideal dielectric (no loss), vacuum, air, polytetrafluoroethylene (PTFE), polyethylene foam, and solid polyethylene. An inhomogeneous dielectric needs to be compensated by a non-circular conductor to avoid current hot-spots. | Coaxial cable | Wikipedia | 492 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
While many cables have a solid dielectric, many others have a foam dielectric that contains as much air or other gas as possible to reduce the losses by allowing the use of a larger diameter center conductor. Foam coax will have about 15% less attenuation but some types of foam dielectric can absorb moisture—especially at its many surfaces—in humid environments, significantly increasing the loss. Supports shaped like stars or spokes are even better but more expensive and very susceptible to moisture infiltration. Still more expensive were the air-spaced coaxials used for some inter-city communications in the mid-20th century. The center conductor was suspended by polyethylene discs every few centimeters. In some low-loss coaxial cables such as the RG-62 type, the inner conductor is supported by a spiral strand of polyethylene, so that an air space exists between most of the conductor and the inside of the jacket. The lower dielectric constant of air allows for a greater inner diameter at the same impedance and a greater outer diameter at the same cutoff frequency, lowering ohmic losses. Inner conductors are sometimes silver-plated to smooth the surface and reduce losses due to skin effect. A rough surface extends the current path and concentrates the current at peaks, thus increasing ohmic loss.
The insulating jacket can be made from many materials. A common choice is PVC, but some applications may require fire-resistant materials. Outdoor applications may require the jacket to resist ultraviolet light, oxidation, rodent damage, or direct burial. Flooded coaxial cables use a water-blocking gel to protect the cable from water infiltration through minor cuts in the jacket. For internal chassis connections the insulating jacket may be omitted.
Signal propagation | Coaxial cable | Wikipedia | 360 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Twin-lead transmission lines have the property that the electromagnetic wave propagating down the line extends into the space surrounding the parallel wires. These lines have low loss, but also have undesirable characteristics. They cannot be bent, tightly twisted, or otherwise shaped without changing their characteristic impedance, causing reflection of the signal back toward the source. They also cannot be buried or run along or attached to anything conductive, as the extended fields will induce currents in the nearby conductors causing unwanted radiation and detuning of the line. Standoff insulators are used to keep them away from parallel metal surfaces. Coaxial lines largely solve this problem by confining virtually all of the electromagnetic wave to the area inside the cable. Coaxial lines can therefore be bent and moderately twisted without negative effects, and they can be strapped to conductive supports without inducing unwanted currents in them, so long as provisions are made to ensure differential signalling push-pull currents in the cable.
In radio-frequency applications up to a few gigahertz, the wave propagates primarily in the transverse electric magnetic (TEM) mode, which means that the electric and magnetic fields are both perpendicular to the direction of propagation. However, above a certain cutoff frequency, transverse electric (TE) or transverse magnetic (TM) modes can also propagate, as they do in a hollow waveguide. It is usually undesirable to transmit signals above the cutoff frequency, since it may cause multiple modes with different phase velocities to propagate, interfering with each other. The outer diameter is roughly inversely proportional to the cutoff frequency. A propagating surface-wave mode that only involves the central conductor also exists, but is effectively suppressed in coaxial cable of conventional geometry and common impedance. Electric field lines for this TM mode have a longitudinal component and require line lengths of a half-wavelength or longer.
Coaxial cable may be viewed as a type of waveguide. Power is transmitted through the radial electric field and the circumferential magnetic field in the TEM mode. This is the dominant mode from zero frequency (DC) to an upper limit determined by the electrical dimensions of the cable.
Connectors | Coaxial cable | Wikipedia | 456 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Coaxial connectors are designed to maintain a coaxial form across the connection and have the same impedance as the attached cable. Connectors are usually plated with high-conductivity metals such as silver or tarnish-resistant gold. Due to the skin effect, the RF signal is only carried by the plating at higher frequencies and does not penetrate to the connector body. Silver however tarnishes quickly and the silver sulfide that is produced is poorly conductive, degrading connector performance, making silver a poor choice for this application.
Important parameters
Coaxial cable is a particular kind of transmission line, so the circuit models developed for general transmission lines are appropriate. See Telegrapher's equation.
Physical parameters
In the following section, these symbols are used:
Length of the cable,
Outside diameter of inner conductor,
Inside diameter of the shield,
Dielectric constant of the insulator, The dielectric constant is often quoted as the relative dielectric constant referred to the dielectric constant of free space When the insulator is a mixture of different dielectric materials (e.g., polyethylene foam is a mixture of polyethylene and air), then the term effective dielectric constant is often used.
Magnetic permeability of the insulator, Permeability is often quoted as the relative permeability referred to the permeability of free space The relative permeability will almost always be .
Fundamental electrical parameters
Shunt capacitance per unit length, in farads per metre.
Series inductance per unit length, in henries per metre, considering the central conductor to be a thin hollow cylinder (due to skin effect).
Series resistance per unit length, in ohms per metre. The resistance per unit length is just the resistance of inner conductor and the shield at low frequencies. At higher frequencies, skin effect increases the effective resistance by confining the conduction to a thin layer of each conductor.
Shunt conductance per unit length, in siemens per metre. The shunt conductance is usually very small because insulators with good dielectric properties are used (a very low loss tangent). At high frequencies, a dielectric can have a significant resistive loss.
Derived electrical parameters
Characteristic impedance in ohms (Ω). The complex impedance of an infinite length of transmission line is: | Coaxial cable | Wikipedia | 486 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Where is the resistance per unit length, is the inductance per unit length, is the conductance per unit length of the dielectric, is the capacitance per unit length, and is the frequency. The "per unit length" dimensions cancel out in the impedance formula.
At DC the two reactive terms are zero, so the impedance is real-valued, and is extremely high. It looks like
With increasing frequency, the reactive components take effect and the impedance of the line is complex-valued. At very low frequencies (audio range, of interest to telephone systems) is typically much smaller than , so the impedance at low frequencies is
which has a phase value of -45 degrees.
At higher frequencies, the reactive terms usually dominate and , and the cable impedance again becomes real-valued. That value is , the characteristic impedance of the cable:
Assuming the dielectric properties of the material inside the cable do not vary appreciably over the operating range of the cable, the characteristic impedance is frequency independent above about five times the shield cutoff frequency. For typical coaxial cables, the shield cutoff frequency is 600 Hz (for RG-6A) to 2,000 Hz (for RG-58C).
The parameters and are determined from the ratio of the inner () and outer () diameters and the dielectric constant (). The characteristic impedance is given by
Attenuation (loss) per unit length, in decibels per meter. This is dependent on the loss in the dielectric material filling the cable, and resistive losses in the center conductor and outer shield. These losses are frequency dependent, the losses becoming higher as the frequency increases. Skin effect losses in the conductors can be reduced by increasing the diameter of the cable. A cable with twice the diameter will have half the skin effect resistance. Ignoring dielectric and other losses, the larger cable would halve the dB/meter loss. In designing a system, engineers consider not only the loss in the cable but also the loss in the connectors.
Velocity of propagation, in meters per second. The velocity of propagation depends on the dielectric constant and permeability (which is usually ). | Coaxial cable | Wikipedia | 459 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Single-mode band. In coaxial cable, the dominant mode (the mode with the lowest cutoff frequency) is the TEM mode, which has a cutoff frequency of zero; it propagates all the way down to DC. The mode with the next lowest cutoff is the TE mode. This mode has one 'wave' (two reversals of polarity) in going around the circumference of the cable. To a good approximation, the condition for the TE mode to propagate is that the wavelength in the dielectric is no longer than the average circumference of the insulator; that is that the frequency is at least
Hence, the cable is single-mode from DC up to this frequency, and might in practice be used up to 90% of this frequency.
Peak Voltage. The peak voltage is set by the breakdown voltage of the insulator.:
where
is the peak voltage
is the insulator's breakdown voltage in volts per meter
is the inner diameter in meters
is the outer diameter in meters
The calculated peak voltage is often reduced by a safety factor. | Coaxial cable | Wikipedia | 226 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Choice of impedance
The best coaxial cable impedances were experimentally determined at Bell Laboratories in 1929 to be 77 Ω for low-attenuation, 60 Ω for high-voltage, and 30 Ω for high-power. For a coaxial cable with air dielectric and a shield of a given inner diameter, the attenuation is minimized by choosing the diameter of the inner conductor to give a characteristic impedance of 76.7 Ω. When more common dielectrics are considered, the lowest insertion loss impedance drops down to a value between 52 and 64 Ω. Maximum power handling is achieved at 30 Ω.
The approximate impedance required to match a centre-fed dipole antenna in free space (i.e., a dipole without ground reflections) is 73 Ω, so 75 Ω coax was commonly used for connecting shortwave antennas to receivers. These typically involve such low levels of RF power that power-handling and high-voltage breakdown characteristics are unimportant when compared to attenuation. Likewise with CATV, although many broadcast TV installations and CATV headends use 300 Ω folded dipole antennas to receive off-the-air signals, 75 Ω coax makes a convenient 4:1 balun transformer for these as well as possessing low attenuation.
The arithmetic mean between 30 Ω and 77 Ω is 53.5 Ω; the geometric mean is 48 Ω. The selection of 50 Ω as a compromise between power-handling capability and attenuation is in general cited as the reason for the number. 50 Ω also works out tolerably well because it corresponds approximately to the feedpoint impedance of a half-wave dipole, mounted approximately a half-wave above "normal" ground (ideally 73 Ω, but reduced for low-hanging horizontal wires).
RG-62 is a 93 Ω coaxial cable originally used in mainframe computer networks in the 1970s and early 1980s (it was the cable used to connect IBM 3270 terminals to IBM 3274/3174 terminal cluster controllers). Later, some manufacturers of LAN equipment, such as Datapoint for ARCNET, adopted RG-62 as their coaxial cable standard. The cable has the lowest capacitance per unit-length when compared to other coaxial cables of similar size. | Coaxial cable | Wikipedia | 475 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
All of the components of a coaxial system should have the same impedance to avoid internal reflections at connections between components (see Impedance matching). Such reflections may cause signal attenuation. They introduce standing waves, which increase losses and can even result in cable dielectric breakdown with high-power transmission. In analog video or TV systems, reflections cause ghosting in the image; multiple reflections may cause the original signal to be followed by more than one echo. If a coaxial cable is open (not connected at the end), the termination has nearly infinite resistance, which causes reflections. If the coaxial cable is short-circuited, the termination resistance is nearly zero, which causes reflections with the opposite polarity. Reflections will be nearly eliminated if the coaxial cable is terminated in a pure resistance equal to its impedance.
Issues
Signal leakage
Signal leakage is the passage of electromagnetic fields through the shield of a cable and occurs in both directions. Ingress is the passage of an outside signal into the cable and can result in noise and disruption of the desired signal. Egress is the passage of signal intended to remain within the cable into the outside world and can result in a weaker signal at the end of the cable and radio frequency interference to nearby devices. Severe leakage usually results from improperly installed connectors or faults in the cable shield.
For example, in the United States, signal leakage from cable television systems is regulated by the FCC, since cable signals use the same frequencies as aeronautical and radionavigation bands. CATV operators may also choose to monitor their networks for leakage to prevent ingress. Outside signals entering the cable can cause unwanted noise and picture ghosting. Excessive noise can overwhelm the signal, making it useless. In-channel ingress can be digitally removed by ingress cancellation.
An ideal shield would be a perfect conductor with no holes, gaps, or bumps connected to a perfect ground. However, a smooth solid highly conductive shield would be heavy, inflexible, and expensive. Such coax is used for straight-line feeds to commercial radio broadcast towers. More economical cables must make compromises between shield efficacy, flexibility, and cost, such as the corrugated surface of flexible hardline, flexible braid, or foil shields. Since shields cannot be perfect conductors, current flowing on the inside of the shield produces an electromagnetic field on the outer surface of the shield. | Coaxial cable | Wikipedia | 494 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Consider the skin effect. The magnitude of an alternating current in a conductor decays exponentially with distance beneath the surface, with the depth of penetration being proportional to the square root of the resistivity. This means that, in a shield of finite thickness, some small amount of current will still be flowing on the opposite surface of the conductor. With a perfect conductor (i.e., zero resistivity), all of the current would flow at the surface, with no penetration into and through the conductor. Real cables have a shield made of an imperfect, although usually very good, conductor, so there must always be some leakage.
The gaps or holes, allow some of the electromagnetic field to penetrate to the other side. For example, braided shields have many small gaps. The gaps are smaller when using a foil (solid metal) shield, but there is still a seam running the length of the cable. Foil becomes increasingly rigid with increasing thickness, so a thin foil layer is often surrounded by a layer of braided metal, which offers greater flexibility for a given cross-section.
Signal leakage can be severe if there is poor contact at the interface to connectors at either end of the cable or if there is a break in the shield.
To greatly reduce signal leakage into or out of the cable, by a factor of 1000, or even 10,000, superscreened cables are often used in critical applications, such as for neutron flux counters in nuclear reactors.
Superscreened cables for nuclear use are defined in IEC 96-4-1, 1990, however as there have been long gaps in the construction of nuclear power stations in Europe, many existing installations are using superscreened cables to the UK standard AESS(TRG) 71181 which is referenced in IEC 61917.
Ground loops
A continuous current, even if small, along the imperfect shield of a coaxial cable can cause visible or audible interference. In CATV systems distributing analog signals the potential difference between the coaxial network and the electrical grounding system of a house can cause a visible "hum bar" in the picture. This appears as a wide horizontal distortion bar in the picture that scrolls slowly upward. Such differences in potential can be reduced by proper bonding to a common ground at the house. See ground loop.
Noise | Coaxial cable | Wikipedia | 468 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
External fields create a voltage across the inductance of the outside of the outer conductor between sender and receiver. The effect is less when there are several parallel cables, as this reduces the inductance and, therefore, the voltage. Because the outer conductor carries the reference potential for the signal on the inner conductor, the receiving circuit measures the wrong voltage.
Transformer effect
The transformer effect is sometimes used to mitigate the effect of currents induced in the shield. The inner and outer conductors form the primary and secondary winding of the transformer, and the effect is enhanced in some high-quality cables that have an outer layer of mu-metal. Because of this 1:1 transformer, the aforementioned voltage across the outer conductor is transformed onto the inner conductor so that the two voltages can be cancelled by the receiver. Many senders and receivers have means to reduce the leakage even further. They increase the transformer effect by passing the whole cable through a ferrite core one or more times.
Common mode current and radiation
Common mode current occurs when stray currents in the shield flow in the same direction as the current in the center conductor, causing the coax to radiate. They are the opposite of the desired "push-pull" differential signalling currents, where the signal currents on the inner and outer conductor are equal and opposite.
Most of the shield effect in coax results from opposing currents in the center conductor and shield creating opposite magnetic fields that cancel, and thus do not radiate. The same effect helps ladder line. However, ladder line is extremely sensitive to surrounding metal objects, which can enter the fields before they completely cancel. Coax does not have this problem, since the field is enclosed in the shield. However, it is still possible for a field to form between the shield and other connected objects, such as the antenna the coax feeds. The current formed by the field between the antenna and the coax shield would flow in the same direction as the current in the center conductor, and thus not be canceled. Energy would radiate from the coax itself, affecting the radiation pattern of the antenna. With sufficient power, this could be a hazard to people near the cable. A properly placed and properly sized balun can prevent common-mode radiation in coax. An isolating transformer or blocking capacitor can be used to couple a coaxial cable to equipment, where it is desirable to pass radio-frequency signals but to block direct current or low-frequency power. | Coaxial cable | Wikipedia | 508 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Higher impedance at audio frequencies
The characteristic impedance formula above is a good approximation at radio frequencies however for frequencies below 100 kHz (such as audio) it becomes important to use the complete telegrapher's equation:
Applying this formula to typical 75 ohm coax we find the measured impedance across the audio spectrum will range from ~150 ohms to ~5K ohms, much higher than nominal. The velocity of propagation also slows considerably. Thus we can expect coax cable impedances to be consistent at RF frequencies but variable across audio frequencies. This effect was manifested when trying to send a plain voice signal across the transatlantic telegraph cable, with poor results.
Standards
Most coaxial cables have a characteristic impedance of either 50, 52, 75, or 93 Ω. The RF industry uses standard type-names for coaxial cables. Thanks to television, RG-6 is the most commonly used coaxial cable for home use, and the majority of connections outside Europe are by F connectors.
A series of standard types of coaxial cable were specified for military uses, in the form "RG-#" or "RG-#/U". They date from World War II and were listed in MIL-HDBK-216 published in 1962. These designations are now obsolete. The RG designation stands for Radio Guide; the U designation stands for Universal. The current military standard is MIL-SPEC MIL-C-17. MIL-C-17 numbers, such as "M17/75-RG214", are given for military cables and manufacturer's catalog numbers for civilian applications. However, the RG-series designations were so common for generations that they are still used, although critical users should be aware that since the handbook is withdrawn there is no standard to guarantee the electrical and physical characteristics of a cable described as "RG-# type". The RG designators are mostly used to identify compatible connectors that fit the inner conductor, dielectric, and jacket dimensions of the old RG-series cables.
Dielectric material codes
FPE is foamed polyethylene
PE is solid polyethylene
PF is polyethylene foam
PTFE is polytetrafluoroethylene;
ASP is air space polyethylene
VF is the Velocity Factor; it is determined by the effective and | Coaxial cable | Wikipedia | 488 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
VF for solid PE is about 0.66
VF for foam PE is about 0.78 to 0.88
VF for air is about 1.00
VF for solid PTFE is about 0.70
VF for foam PTFE is about 0.84
There are also other designation schemes for coaxial cables such as the URM, CT, BT, RA, PSF and WF series.
Uses
Short coaxial cables are commonly used to connect home video equipment, in ham radio setups, and in Nuclear Instrumentation Modules. While formerly common for implementing computer networks, in particular Ethernet ("thick" 10BASE5 and "thin" 10BASE2), twisted pair cables have replaced them in most applications except in the consumer cable modem market for broadband Internet access.
Long distance coaxial cable was used in the 20th century to connect radio networks, television networks, and long-distance telephone networks though this has largely been superseded by later methods (fibre optics, T1/E1, satellite).
Shorter coaxials still carry cable television signals to the majority of television receivers, and this purpose consumes the majority of coaxial cable production. In 1980s and early 1990s coaxial cable was also used in computer networking, most prominently in Ethernet networks, where it was later in late 1990s to early 2000s replaced by UTP cables in North America and STP cables in Western Europe, both with 8P8C modular connectors.
Micro coaxial cables are used in a range of consumer devices, military equipment, and also in ultrasound scanning equipment.
The most common impedances that are widely used are 50 or 52 ohms and 75 ohms, although other impedances are available for specific applications. The 50 / 52 ohm cables are widely used for industrial and commercial two-way radio frequency applications (including radio, and telecommunications), although 75 ohms is commonly used for broadcast television and radio.
Coaxial cable is often used to carry signals from an antenna to a receiver. In many cases, the same cable carries power toward the antenna, to power a preamplifier. In some cases, a single cable carries unidirectional power and bidirectional data/signals, as in DiSEqC.
Types
Hard line | Coaxial cable | Wikipedia | 466 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Larger varieties of hardline may have a center conductor that is constructed from either rigid or corrugated copper tubing. The dielectric in hard line may consist of polyethylene foam, air, or a pressurized gas such as nitrogen or desiccated air (dried air). In gas-charged lines, hard plastics such as nylon are used as spacers to separate the inner and outer conductors. The addition of these gases into the dielectric space reduces moisture contamination, provides a stable dielectric constant, and provides a reduced risk of internal arcing. Gas-filled hardlines are usually used on high-power RF transmitters such as television or radio broadcasting, military transmitters, and high-power amateur radio applications but may also be used on some critical lower-power applications such as those in the microwave bands. However, in the microwave region, waveguide is more often used than hard line for transmitter-to-antenna, or antenna-to-receiver applications. The various shields used in hard line also differ; some forms use rigid tubing, or pipe, while others may use a corrugated tubing, which makes bending easier, as well as reduces kinking when the cable is bent to conform. Smaller varieties of hard line may be used internally in some high-frequency applications, in particular in equipment within the microwave range, to reduce interference between stages of the device.
Radiating
Radiating or leaky cable is another form of coaxial cable which is constructed in a similar fashion to hard line, however it is constructed with tuned slots cut into the shield. These slots are tuned to the specific RF wavelength of operation or tuned to a specific radio frequency band. This type of cable is to provide a tuned bi-directional "desired" leakage effect between transmitter and receiver. It is often used in elevator shafts, US Navy Ships, underground transportation tunnels and in other areas where an antenna is not feasible. One example of this type of cable is Radiax (CommScope).
RG-6 | Coaxial cable | Wikipedia | 406 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
RG-6 is available in four different types designed for various applications. In addition, the core may be copper clad steel (CCS) or bare solid copper (BC). "Plain" or "house" RG-6 is designed for indoor or external house wiring. "Flooded" cable is infused with water-blocking gel for use in underground conduit or direct burial. "Messenger" may contain some waterproofing but is distinguished by the addition of a steel messenger wire along its length to carry the tension involved in an aerial drop from a utility pole. "Plenum" cabling is expensive and comes with a special Teflon-based outer jacket designed for use in ventilation ducts to meet fire codes. It was developed since the plastics used as the outer jacket and inner insulation in many "Plain" or "house" cabling gives off poisonous gas when burned.
Triaxial cable
Triaxial cable or triax is coaxial cable with a third layer of shielding, insulation and sheathing. The outer shield, which is earthed (grounded), protects the inner shield from electromagnetic interference from outside sources.
Semi-rigid
Semi-rigid cable is a coaxial form using a solid copper outer sheath. This type of coax offers superior screening compared to cables with a braided outer conductor, especially at higher frequencies. The major disadvantage is that the cable, as its name implies, is not very flexible, and is not intended to be flexed after initial forming. (See )
Conformable cable is a flexible reformable alternative to semi-rigid coaxial cable used where flexibility is required. Conformable cable can be stripped and formed by hand without the need for specialized tools, similar to standard coaxial cable.
Rigid line | Coaxial cable | Wikipedia | 357 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Rigid line is a coaxial line formed by two copper tubes maintained concentric every other meter using PTFE-supports. Rigid lines cannot be bent, so they often need elbows. Interconnection with rigid line is done with an inner bullet/inner support and a flange or connection kit. Typically, rigid lines are connected using standardised EIA RF Connectors whose bullet and flange sizes match the standard line diameters. For each outer diameter, either 75 or 50 ohm inner tubes can be obtained.
Rigid line is commonly used indoors for interconnection between high-power transmitters and other RF-components, but more rugged rigid line with weatherproof flanges is used outdoors on antenna masts, etc. In the interests of saving weight and costs, on masts and similar structures the outer line is often aluminium, and special care must be taken to prevent corrosion.
With a flange connector, it is also possible to go from rigid line to hard line. Many broadcasting antennas and antenna splitters use the flanged rigid line interface even when connecting to flexible coaxial cables and hard line.
Rigid line is produced in a number of different sizes:
Interference and troubleshooting
Coaxial cable insulation may degrade, requiring replacement of the cable, especially if it has been exposed to the elements on a continuous basis. The shield is normally grounded, and if even a single thread of the braid or filament of foil touches the center conductor, the signal will be shorted causing significant or total signal loss. This most often occurs at improperly installed end connectors and splices. Also, the connector or splice must be properly attached to the shield, as this provides the path to ground for the interfering signal. | Coaxial cable | Wikipedia | 353 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Despite being shielded, interference can occur on coaxial cable lines. Susceptibility to interference has little relationship to broad cable type designations (e.g. RG-59, RG-6) but is strongly related to the composition and configuration of the cable's shielding. For cable television, with frequencies extending well into the UHF range, a foil shield is normally provided, and will provide total coverage as well as high effectiveness against high-frequency interference. Foil shielding is ordinarily accompanied by a tinned copper or aluminum braid shield, with anywhere from 60 to 95% coverage. The braid is important to shield effectiveness because (1) it is more effective than foil at preventing low-frequency interference, (2) it provides higher conductivity to ground than foil, and (3) it makes attaching a connector easier and more reliable. "Quad-shield" cable, using two low-coverage aluminum braid shields and two layers of foil, is often used in situations involving troublesome interference, but is less effective than a single layer of foil and single high-coverage copper braid shield such as is found on broadcast-quality precision video cable.
In the United States and some other countries, cable television distribution systems use extensive networks of outdoor coaxial cable, often with in-line distribution amplifiers. Leakage of signals into and out of cable TV systems can cause interference to cable subscribers and to over-the-air radio services using the same frequencies as those of the cable system.
History | Coaxial cable | Wikipedia | 303 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
1858 — Coaxial cable used in first (1858) transatlantic cable.
1880 — Coaxial cable patented in England by Oliver Heaviside, patent no. 1,407.
1884 — Siemens & Halske patent coaxial cable in Germany (Patent No. 28,978, 27 March 1884).
1894 — Nikola Tesla (U.S. Patent 514,167)
1929 — First modern coaxial cable patented by Lloyd Espenschied and Herman Affel of AT&T's Bell Telephone Laboratories.
1936 — First closed circuit transmission of TV pictures on coaxial cable, from the 1936 Summer Olympics in Berlin to Leipzig.
1936 — Underwater coaxial cable installed between Apollo Bay, near Melbourne, Australia, and Stanley, Tasmania. The cable can carry one 8.5-kHz broadcast channel and seven telephone channels.
1936 — AT&T installs experimental coaxial telephone and television cable between New York and Philadelphia, with automatic booster stations every . Completed in December, it can transmit 240 telephone calls simultaneously.
1936 — Coaxial cable laid by the General Post Office (now BT) between London and Birmingham, providing 40 telephone channels.
1941 — First commercial use in US by AT&T, between Minneapolis, Minnesota and Stevens Point, Wisconsin. L1 system with capacity of one TV channel or 480 telephone circuits.
1949 — On January 11, eight stations on the US East Coast and seven Midwestern stations are linked via a long-distance coaxial cable.
1956 — First transatlantic telephone coaxial cable laid, TAT-1.
1962 — Sydney–Melbourne co-axial cable commissioned, carrying 3 x 1,260 simultaneous telephone connections, and-or simultaneous inter-city television transmission. | Coaxial cable | Wikipedia | 350 | 46380 | https://en.wikipedia.org/wiki/Coaxial%20cable | Technology | Signal transmission | null |
Magenta () is a purplish-red color. On color wheels of the RGB (additive) and CMY (subtractive) color models, it is located precisely midway between blue and red. It is one of the four colors of ink used in color printing by an inkjet printer, along with yellow, cyan, and black to make all the other colors. The tone of magenta used in printing, printer's magenta, is redder than the magenta of the RGB (additive) model, the former being closer to rose.
Magenta took its name from an aniline dye made and patented in 1859 by the French chemist François-Emmanuel Verguin, who originally called it fuchsine. It was renamed to celebrate the Italian-French victory at the Battle of Magenta fought between the French and Austrians on 4 June 1859 near the Italian town of Magenta in Lombardy. A virtually identical color, called roseine, was created in 1860 by two British chemists, Edward Chambers Nicholson, and George Maule.
The web color magenta is also called fuchsia.
In optics and color science
Magenta is an extra-spectral color, meaning that it is not a hue associated with monochromatic visible light. Magenta is associated with perception of spectral power distributions concentrated mostly in two bands: longer wavelength reddish components and shorter wavelength blueish components.
In the RGB color system, used to create all the colors on a television or computer display, magenta is a secondary color, made by combining equal amounts of red and blue light at a high intensity. In this system, magenta is the complementary color of green, and combining green and magenta light on a black screen will create white.
In the CMYK color model, used in color printing, it is one of the three primary colors, along with cyan and yellow, used to print all the rest of the colors. If magenta, cyan, and yellow are printed on top of each other on a page, they make black. In this model, magenta is the complementary color of green. If combined, green and magenta ink will look dark brown or black. The magenta used in color printing, sometimes called process magenta, is a darker shade than the color used on computer screens. | Magenta | Wikipedia | 470 | 46408 | https://en.wikipedia.org/wiki/Magenta | Physical sciences | Colors | Physics |
In terms of physiology, the color is stimulated in the brain when the eye reports input from short wave blue cone cells along with a sub-sensitivity of the long wave cones which respond secondarily to that same deep blue color, but with little or no input from the middle wave cones. The brain interprets that combination as some hue of magenta or purple, depending on the relative strengths of the cone responses.
In the Munsell color system, magenta is called red-purple.
If the spectrum is wrapped to form a color wheel, magenta (additive secondary) appears midway between red and violet. Violet and red, the two components of magenta, are at opposite ends of the visible spectrum and have very different wavelengths. The additive secondary color magenta is made by combining violet and red light at equal intensity; it is not present in the spectrum itself.
Fuchsia and magenta
The web colors fuchsia and magenta are identical, made by mixing the same proportions of blue and red light. In design and printing, there is more variation. The French version of fuchsia in the RGB color model and in printing contains a higher proportion of red than the American version of fuchsia.
Gallery
History
Fuchsine and magenta dye (1859)
The color magenta was the result of the industrial chemistry revolution of the mid-nineteenth century, which began with the invention by William Perkin of mauveine in 1856, which was the first synthetic aniline dye. The enormous commercial success of the dye and the new color it produced, mauve, inspired other chemists in Europe to develop new colors made from aniline dyes.
In France, François-Emmanuel Verguin, the director of the chemical factory of Louis Rafard near Lyon, tried many different formulae before finally in late 1858 or early 1859, mixing aniline with carbon tetrachloride, producing a reddish-purple dye which he called "fuchsine", after the color of the flower of the fuchsia plant. He quit the Rafard factory and took his color to a firm of paint manufacturers, Francisque and Joseph Renard, who began to manufacture the dye in 1859. | Magenta | Wikipedia | 448 | 46408 | https://en.wikipedia.org/wiki/Magenta | Physical sciences | Colors | Physics |
In the same year, two British chemists, Edward Chambers Nicholson and George Maule, working at the laboratory of the paint manufacturer George Simpson, located in Walworth, south of London, made another aniline dye with a similar red-purple color, which they began to manufacture in 1860 under the name "roseine". In 1860, they changed the name of the color to "magenta", in honor of the Battle of Magenta fought by the armies of France and Sardinia against Austrians at Magenta, Lombardy the year before, and the new color became a commercial success.
Starting in 1935, the family of quinacridone dyes was developed. These have colors ranging from red to violet, so nowadays a quinacridone dye is often used for magenta. Various tones of magenta—light, bright, brilliant, vivid, rich, or deep—may be formulated by adding varying amounts of white to quinacridone artist's paints.
Another dye used for magenta is Lithol Rubine BK. One of its uses is as a food coloring.
Process magenta (pigment magenta; printer's magenta) (1890s)
In color printing, the color called process magenta, pigment magenta, or printer's magenta is one of the three primary pigment colors which, along with yellow and cyan, constitute the three subtractive primary colors of pigment. (The secondary colors of pigment are blue, green, and red.) As such, the hue magenta is the complement of green: magenta pigments absorb green light; thus magenta and green are opposite colors.
The CMYK printing process was invented in the 1890s, when newspapers began to publish color comic strips.
Process magenta is not an RGB color, and there is no fixed conversion from CMYK primaries to RGB. Different formulations are used for printer's ink, so there may be variations in the printed color that is pure magenta ink.
Web colors magenta and fuchsia
The web color magenta is one of the three secondary colors in the RGB color model.
On the RGB color wheel, magenta is the color between rose and violet, and halfway between red and blue. | Magenta | Wikipedia | 453 | 46408 | https://en.wikipedia.org/wiki/Magenta | Physical sciences | Colors | Physics |
This color is called magenta in X11 and fuchsia in HTML. In the RGB color model, it is created by combining equal intensities of red and blue light. The two web colors magenta and fuchsia are exactly the same color. Sometimes the web color magenta is called electric magenta or electronic magenta.
While the magenta used in printing and the web color have the same name, they have important differences. Process magenta (the color used for magenta printing ink—also called printer's or pigment magenta) is much less vivid than the color magenta achievable on a computer screen. CMYK printing technology cannot accurately reproduce on paper the color on the computer screen. When the web color magenta is reproduced on paper, it is called fuchsia and it is physically impossible for it to appear on paper as vivid as on a computer screen.
Colored pencils and crayons called "magenta" are usually colored the color of process magenta (printer's magenta).
In science and culture
In art
Paul Gauguin (1848–1903) used a shade of magenta in 1890 in his portrait of Marie Lagadu, and in some of his South Seas paintings.
Henri Matisse and the members of the Fauvist movement used magenta and other non-traditional colors to surprise viewers, and to move their emotions through the use of bold colors.
Since the mid-1960s, water based fluorescent magenta paint has been available to paint psychedelic black light paintings. (Fluorescent cerise, fluorescent chartreuse yellow, fluorescent blue, and fluorescent green.)
In literature
The color plays a central role in Craig Laurance Gidney's novel A Spectral Hue.
In film
The titular alien entity in the 2019 horror film Color Out of Space, an adaptation of the 1927 H. P. Lovecraft short story The Colour Out of Space, is depicted as being magenta due to the color's extra-spectral status.
In astronomy
Astronomers have reported that spectral class T brown dwarfs (the ones with the coolest temperatures except for the recently discovered Y brown dwarfs) are colored magenta because of absorption by sodium and potassium atoms of light in the green portion of the spectrum.
In biology: magenta insects, birds, fish, and mammals | Magenta | Wikipedia | 470 | 46408 | https://en.wikipedia.org/wiki/Magenta | Physical sciences | Colors | Physics |
In botany
Magenta is a common color for flowers, particularly in the tropics and sub-tropics. Because magenta is the complementary color of green, magenta flowers have the highest contrast with the green foliage, and therefore are more visible to the animals needed for their pollination.
In business
The German telecommunications company Deutsche Telekom uses a magenta logo. It has sought to prevent use of any similar color by other businesses, even those in unrelated fields, such as the insurance company Lemonade.
In public transport
Magenta was the English name of Tokyo's Oedo subway line color. It was later changed to ruby.
It is also the color of the Metropolitan line of the London Underground.
In transportation
In aircraft autopilot systems, the path that pilot or plane should follow to its destination is usually indicated in cockpit displays using the color magenta.
In numismatics
The Reserve Bank of India (RBI) issued a Magenta colored banknote of ₹2000 denomination on 8 November 2016 under Mahatma Gandhi New Series. This is the highest currency note printed by RBI that is in active circulation in India.
In vexillology and heraldry
Magenta is an extremely rare color to find on heraldic flags and coats of arms, since its adoption dates back to relatively recent times. However, there are some examples of its use:
In politics
Throughout much of Europe, the color of magenta (or variants of such, such as Pink or Amaranth) is used to symbolise social liberalism or classical liberalism
The color magenta is used to symbolize anti-racism by the Amsterdam-based anti-racism Magenta Foundation.
In Danish politics, magenta is the color of Det Radikale Venstre, the Danish social-liberal party.
In Austrian politics, it is used to represent NEOS – The New Austria and Liberal Forum, a social liberal party.
In Belgium, it is used by DéFI, a social liberal party.
In Germany, Magenta is one of the colors of the Free Democratic Party, or FDP. | Magenta | Wikipedia | 418 | 46408 | https://en.wikipedia.org/wiki/Magenta | Physical sciences | Colors | Physics |
A crayon (or wax pastel) is a stick of pigmented wax used for writing or drawing. Wax crayons differ from pastels, in which the pigment is mixed with a dry binder such as gum arabic, and from oil pastels, where the binder is a mixture of wax and oil.
Crayons are available in a range of prices, and are easy to work with. They are less messy than most paints and markers, blunt (removing the risk of sharp points present when using a pencil or pen), typically non-toxic, and available in a wide variety of colors. These characteristics make them particularly good instruments for teaching small children to draw in addition to being used widely by student and professional artists.
Composition
In the modern English-speaking world, the term crayon is commonly associated with the standard wax crayon, such as those widely available for use by children. Such crayons are usually approximately in length and made mostly of paraffin wax. Paraffin wax is heated and cooled to achieve the correct temperature at which a usable wax substance can be dyed and then manufactured and shipped for use around the world. Paraffin waxes are used for cosmetics, candles, for the preparation of printing ink, fruit preserving, in the pharmaceutical industry, for lubricating purposes, and crayons.
Colin Snedeker, a chemist for Binney & Smith (the then-parent company of Crayola), developed the first washable crayons in response to consumer complaints regarding stained fabrics and walls. A patent for the washable solid marking composition utilized in the washable crayons was awarded to Snedeker in 1990.
History
The history of the crayon is not entirely clear. The French word crayon, originally meaning "chalk pencil", dates to around the 16th century, and is derived from the word craie (chalk), which comes from the Latin word creta (Earth). The meaning later changed to simply "pencil", which it still means in modern French.
The notion to combine a form of wax with pigment goes back thousands of years. Encaustic painting is a technique that uses hot beeswax combined with colored pigment to bind color into stone. A heat source was then used to "burn in" and fix the image in place. Pliny the Elder, a Roman scholar, was thought to describe the first techniques of wax crayon drawings. | Crayon | Wikipedia | 500 | 46415 | https://en.wikipedia.org/wiki/Crayon | Technology | Artist's and drafting tools | null |
This method, employed by the Egyptians, Romans, Greeks, and indigenous people in the Philippines, is still used today. However, the process was not used to make crayons into a form intended to be held and colored with and was therefore ineffective for use in a classroom or as crafts for children.
Contemporary crayons are purported to have originated in Europe, where some of the first cylinder shaped crayons were made with charcoal and oil. Pastels are an art medium sharing roots with the modern crayon and date back to Leonardo da Vinci in 1495. Conté crayons, out of Paris, are a hybrid between a pastel and a conventional crayon, used since the late 1790s as a drawing crayon for artists. Later, various hues of powdered pigment eventually replaced the primary charcoal ingredient found in most early 19th century products. | Crayon | Wikipedia | 177 | 46415 | https://en.wikipedia.org/wiki/Crayon | Technology | Artist's and drafting tools | null |
Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. This practice reduces the reliance of crops on one set of nutrients, pest and weed pressure, along with the probability of developing resistant pests and weeds.
Growing the same crop in the same place for many years in a row, known as monocropping, gradually depletes the soil of certain nutrients and selects for both a highly competitive pest and weed community. Without balancing nutrient use and diversifying pest and weed communities, the productivity of monocultures is highly dependent on external inputs that may be harmful to the soil's fertility. Conversely, a well-designed crop rotation can reduce the need for synthetic fertilizers and herbicides by better using ecosystem services from a diverse set of crops. Additionally, crop rotations can improve soil structure and organic matter, which reduces erosion and increases farm system resilience.
History
Farmers have long recognized that suitable rotations such as planting spring crops for livestock in place of grains for human consumption make it possible to restore or to maintain productive soils. Ancient Near Eastern farmers practiced crop rotation in 6000 BC, alternately planting legumes and cereals.
Two-field systems
Under a two-field rotation, half the land was planted in a year, while the other half lay fallow. Then, in the next year, the two fields were reversed. In China both the two- and three-field systems had been used since the Eastern Zhou period.
Three-field systems | Crop rotation | Wikipedia | 309 | 46470 | https://en.wikipedia.org/wiki/Crop%20rotation | Technology | Soil and soil management | null |
From the 9th century to the 11th century, farmers in Europe transitioned from a two-field system to a three-field system. This system persisted until the 20th century. Available land was divided into three sections. One section was planted in the autumn with rye or winter wheat, followed by spring oats or barley; the second section grew crops such as one of the legumes, namely peas, lentils, or beans; and the third field was left fallow. The three fields were rotated in this manner so that every three years, one of the fields would rest and lie fallow. Under the two-field system, only half the land was planted in any year. Under the new three-field rotation system, two thirds of the land was planted, potentially yielding a larger harvest. But the additional crops had a more significant effect than mere quantitative productivity. Since the spring crops were mostly legumes, which fix nitrogen needed for plants to make proteins, they increased the overall nutrition of the people of Europe.
Four-field rotations
Farmers in the region of Waasland (in present-day northern Belgium) pioneered a four-field rotation in the early 16th century, and the British agriculturist Charles Townshend (1674–1738) popularised this system in the 18th century. The sequence of four crops (wheat, turnips, barley and clover), included a fodder crop and a grazing crop, allowing livestock to be bred year-round. The four-field crop rotation became a key development in the British Agricultural Revolution.
Modern developments
George Washington Carver (1860s–1943) studied crop-rotation methods in the United States, teaching southern farmers to rotate soil-depleting crops like cotton with soil-enriching crops like peanuts and peas.
In the Green Revolution of the mid-20th century, crop rotation gave way in the developed world to the practice of supplementing the chemical inputs to the soil through topdressing with fertilizers, adding (for example) ammonium nitrate or urea and restoring soil pH with lime. Such practices aimed to increase yields, to prepare soil for specialist crops, and to reduce waste and inefficiency by simplifying planting, harvesting, and irrigation.
Crop choice
A preliminary assessment of crop interrelationships can be found in how each crop: | Crop rotation | Wikipedia | 474 | 46470 | https://en.wikipedia.org/wiki/Crop%20rotation | Technology | Soil and soil management | null |
Contributes to soil organic matter (SOM) content.
Provides for pest management.
Manages deficient or excess nutrients.
Contributes to or controls for soil erosion.
Interbreeds with other crops to produce hybrid offspring.
Impacts surrounding food webs and field ecosystems.
Crop choice is often related to the goal the farmer is looking to achieve with the rotation, which could be weed management, increasing available nitrogen in the soil, controlling for erosion, or increasing soil structure and biomass, to name a few. When discussing crop rotations, crops are classified in different ways depending on what quality is being assessed: by family, by nutrient needs/benefits, and/or by profitability (i.e. cash crop versus cover crop). For example, giving adequate attention to plant family is essential to mitigating pests and pathogens. However, many farmers have success managing rotations by planning sequencing and cover crops around desirable cash crops. The following is a simplified classification based on crop quality and purpose.
Row crops
Many crops which are critical for the market, like vegetables, are row crops (that is, grown in tight rows). While often the most profitable for farmers, these crops are more taxing on the soil. Row crops typically have low biomass and shallow roots: this means the plant contributes low residue to the surrounding soil and has limited effects on structure. With much of the soil around the plant exposed to disruption by rainfall and traffic, fields with row crops experience faster break down of organic matter by microbes, leaving fewer nutrients for future plants.
In short, while these crops may be profitable for the farm, they are nutrient depleting. Crop rotation practices exist to strike a balance between short-term profitability and long-term productivity.
Legumes
A great advantage of crop rotation comes from the interrelationship of nitrogen-fixing crops with nitrogen-demanding crops. Legumes, like alfalfa and clover, collect available nitrogen from the atmosphere and store it in nodules on their root structure. When the plant is harvested, the biomass of uncollected roots breaks down, making the stored nitrogen available to future crops.
Grasses and cereals
Cereal and grasses are frequent cover crops because of the many advantages they supply to soil quality and structure. The dense and far-reaching root systems give ample structure to surrounding soil and provide significant biomass for soil organic matter.
Grasses and cereals are key in weed management as they compete with undesired plants for soil space and nutrients.
Green manure | Crop rotation | Wikipedia | 505 | 46470 | https://en.wikipedia.org/wiki/Crop%20rotation | Technology | Soil and soil management | null |
Green manure is a crop that is mixed into the soil. Both nitrogen-fixing legumes and nutrient scavengers, like grasses, can be used as green manure. Green manure of legumes is an excellent source of nitrogen, especially for organic systems, however, legume biomass does not contribute to lasting soil organic matter like grasses do.
Planning a rotation
There are numerous factors that must be taken into consideration when planning a crop rotation. Planning an effective rotation requires weighing fixed and fluctuating production circumstances: market, farm size, labor supply, climate, soil type, growing practices, etc. Moreover, a crop rotation must consider in what condition one crop will leave the soil for the succeeding crop and how one crop can be seeded with another crop. For example, a nitrogen-fixing crop, like a legume, should always precede a nitrogen depleting one; similarly, a low residue crop (i.e. a crop with low biomass) should be offset with a high biomass cover crop, like a mixture of grasses and legumes.
There is no limit to the number of crops that can be used in a rotation, or the amount of time a rotation takes to complete. Decisions about rotations are made years prior, seasons prior, or even at the last minute when an opportunity to increase profits or soil quality presents itself.
Implementation
Relationship to other systems
Crop rotation systems may be enriched by other practices such as the addition of livestock and manure, and by growing more than one crop at a time in a field. A monoculture is a crop grown by itself in a field. A polyculture involves two or more crops growing in the same place at the same time. Crop rotations can be applied to both monocultures and polycultures, resulting in multiple ways of increasing agricultural biodiversity (table).
Incorporation of livestock
Introducing livestock makes the most efficient use of critical sod and cover crops; livestock (through manure) are able to distribute the nutrients in these crops throughout the soil rather than removing nutrients from the farm through the sale of hay. | Crop rotation | Wikipedia | 422 | 46470 | https://en.wikipedia.org/wiki/Crop%20rotation | Technology | Soil and soil management | null |
Mixed farming or the practice of crop cultivation with the incorporation of livestock can help manage crops in a rotation and cycle nutrients. Crop residues provide animal feed, while the animals provide manure for replenishing crop nutrients and draft power. These processes promote internal nutrient cycling and minimize the need for synthetic fertilizers and large-scale machinery. As an additional benefit, the cattle, sheep and/or goat provide milk and can act as a cash crop in the times of economic hardship.
Polyculture
Polyculture systems, such as intercropping or companion planting, offer more diversity and complexity within the same season or rotation. An example is the Three Sisters, the inter-planting of corn with pole beans and vining squash or pumpkins. In this system, the beans provide nitrogen; the corn provides support for the beans and a "screen" against squash vine borer; the vining squash provides a weed suppressive canopy and a discouragement for corn-hungry raccoons.
Double-cropping is common where two crops, typically of different species, are grown sequentially in the same growing season, or where one crop (e.g. vegetable) is grown continuously with a cover crop (e.g. wheat). This is advantageous for small farms, which often cannot afford to leave cover crops to replenish the soil for extended periods of time, as larger farms can. When multiple cropping is implemented on small farms, these systems can maximize benefits of crop rotation on available land resources.
Organic farming
Crop rotation is a required practice, in the United States, for farms seeking organic certification. The “Crop Rotation Practice Standard” for the National Organic Program under the U.S. Code of Federal Regulations, section §205.205, states that
In addition to lowering the need for inputs (by controlling for pests and weeds and increasing available nutrients), crop rotation helps organic growers increase the amount of biodiversity their farms. Biodiversity is also a requirement of organic certification, however, there are no rules in place to regulate or reinforce this standard. Increasing the biodiversity of crops has beneficial effects on the surrounding ecosystem and can host a greater diversity of fauna, insects, and beneficial microorganisms in the soil as found by McDaniel et al 2014 and Lori et al 2017. Some studies point to increased nutrient availability from crop rotation under organic systems compared to conventional practices as organic practices are less likely to inhibit of beneficial microbes in soil organic matter. | Crop rotation | Wikipedia | 497 | 46470 | https://en.wikipedia.org/wiki/Crop%20rotation | Technology | Soil and soil management | null |
While multiple cropping and intercropping benefit from many of the same principals as crop rotation, they do not satisfy the requirement under the NOP.
Benefits
Agronomists describe the benefits to yield in rotated crops as "The Rotation Effect". There are many benefits of rotation systems. The factors related to the increase are broadly due to alleviation of the negative factors of monoculture cropping systems. Specifically, improved nutrition; pest, pathogen, and weed stress reduction; and improved soil structure have been found in some cases to be correlated to beneficial rotation effects.
Other benefits include reduced production cost. Overall financial risks are more widely distributed over more diverse production of crops and/or livestock. Less reliance is placed on purchased inputs and over time crops can maintain production goals with fewer inputs. This in tandem with greater short and long term yields makes rotation a powerful tool for improving agricultural systems.
Soil organic matter
The use of different species in rotation allows for increased soil organic matter (SOM), greater soil structure, and improvement of the chemical and biological soil environment for crops. With more SOM, water infiltration and retention improves, providing increased drought tolerance and decreased erosion.
Soil organic matter is a mix of decaying material from biomass with active microorganisms. Crop rotation, by nature, increases exposure to biomass from sod, green manure, and various other plant debris. The reduced need for intensive tillage under crop rotation allows biomass aggregation to lead to greater nutrient retention and utilization, decreasing the need for added nutrients. With tillage, disruption and oxidation of soil creates a less conducive environment for diversity and proliferation of microorganisms in the soil. These microorganisms are what make nutrients available to plants. So, where "active" soil organic matter is a key to productive soil, soil with low microbial activity provides significantly fewer nutrients to plants; this is true even though the quantity of biomass left in the soil may be the same.
Soil microorganisms also decrease pathogen and pest activity through competition. In addition, plants produce root exudates and other chemicals which manipulate their soil environment as well as their weed environment. Thus rotation allows increased yields from nutrient availability but also alleviation of allelopathy and competitive weed environments.
Carbon sequestration | Crop rotation | Wikipedia | 462 | 46470 | https://en.wikipedia.org/wiki/Crop%20rotation | Technology | Soil and soil management | null |
Crop rotations greatly increase soil organic carbon (SOC) content, the main constituent of soil organic matter. Carbon, along with hydrogen and oxygen, is a macronutrient for plants. Highly diverse rotations spanning long periods of time have shown to be even more effective in increasing SOC, while soil disturbances (e.g. from tillage) are responsible for exponential decline in SOC levels. In Brazil, conversion to no-till methods combined with intensive crop rotations has been shown an SOC sequestration rate of 0.41 tonnes per hectare per year.
In addition to enhancing crop productivity, sequestration of atmospheric carbon has great implications in reducing rates of climate change by removing carbon dioxide from the air.
Nitrogen fixing
Rotations can add nutrients to the soil. Legumes, plants of the family Fabaceae, have nodules on their roots which contain nitrogen-fixing bacteria called rhizobia. During a process called nodulation, the rhizobia bacteria use nutrients and water provided by the plant to convert atmospheric nitrogen into ammonia, which is then converted into an organic compound that the plant can use as its nitrogen source. It therefore makes good sense agriculturally to alternate them with cereals (family Poaceae) and other plants that require nitrates. How much nitrogen made available to the plants depends on factors such as the kind of legume, the effectiveness of rhizobia bacteria, soil conditions, and the availability of elements necessary for plant food.
Pathogen and pest control
Crop rotation is also used to control pests and diseases that can become established in the soil over time. The changing of crops in a sequence decreases the population level of pests by (1) interrupting pest life cycles and (2) interrupting pest habitat. Plants within the same taxonomic family tend to have similar pests and pathogens. By regularly changing crops and keeping the soil occupied by cover crops instead of lying fallow, pest cycles can be broken or limited, especially cycles that benefit from overwintering in residue. For example, root-knot nematode is a serious problem for some plants in warm climates and sandy soils, where it slowly builds up to high levels in the soil, and can severely damage plant productivity by cutting off circulation from the plant roots. Growing a crop that is not a host for root-knot nematode for one season greatly reduces the level of the nematode in the soil, thus making it possible to grow a susceptible crop the following season without needing soil fumigation. | Crop rotation | Wikipedia | 505 | 46470 | https://en.wikipedia.org/wiki/Crop%20rotation | Technology | Soil and soil management | null |
This principle is of particular use in organic farming, where pest control must be achieved without synthetic pesticides.
Weed management
Integrating certain crops, especially cover crops, into crop rotations is of particular value to weed management. These crops crowd out weeds through competition. In addition, the sod and compost from cover crops and green manure slows the growth of what weeds are still able to make it through the soil, giving the crops further competitive advantage. By slowing the growth and proliferation of weeds while cover crops are cultivated, farmers greatly reduce the presence of weeds for future crops, including shallow rooted and row crops, which are less resistant to weeds. Cover crops are, therefore, considered conservation crops because they protect otherwise fallow land from becoming overrun with weeds.
This system has advantages over other common practices for weeds management, such as tillage. Tillage is meant to inhibit growth of weeds by overturning the soil; however, this has a countering effect of exposing weed seeds that may have gotten buried and burying valuable crop seeds. Under crop rotation, the number of viable seeds in the soil is reduced through the reduction of the weed population.
In addition to their negative impact on crop quality and yield, weeds can slow down the harvesting process. Weeds make farmers less efficient when harvesting, because weeds like bindweeds, and knotgrass, can become tangled in the equipment, resulting in a stop-and-go type of harvest.
Reducing soil erosion
Crop rotation can significantly reduce the amount of soil lost from erosion by water. In areas that are highly susceptible to erosion, farm management practices such as zero and reduced tillage can be supplemented with specific crop rotation methods to reduce raindrop impact, sediment detachment, sediment transport, surface runoff, and soil loss.
Protection against soil loss is maximized with rotation methods that leave the greatest mass of crop stubble (plant residue left after harvest) on top of the soil. Stubble cover in contact with the soil minimizes erosion from water by reducing overland flow velocity, stream power, and thus the ability of the water to detach and transport sediment. Soil erosion and seal prevent the disruption and detachment of soil aggregates that cause macropores to block, infiltration to decline, and runoff to increase. This significantly improves the resilience of soils when subjected to periods of erosion and stress. | Crop rotation | Wikipedia | 467 | 46470 | https://en.wikipedia.org/wiki/Crop%20rotation | Technology | Soil and soil management | null |
When a forage crop breaks down, binding products are formed that act like an adhesive on the soil, which makes particles stick together, and form aggregates. The formation of soil aggregates is important for erosion control, as they are better able to resist raindrop impact, and water erosion. Soil aggregates also reduce wind erosion, because they are larger particles, and are more resistant to abrasion through tillage practices.
The effect of crop rotation on erosion control varies by climate. In regions under relatively consistent climate conditions, where annual rainfall and temperature levels are assumed, rigid crop rotations can produce sufficient plant growth and soil cover. In regions where climate conditions are less predictable, and unexpected periods of rain and drought may occur, a more flexible approach for soil cover by crop rotation is necessary. An opportunity cropping system promotes adequate soil cover under these erratic climate conditions. In an opportunity cropping system, crops are grown when soil water is adequate and there is a reliable sowing window. This form of cropping system is likely to produce better soil cover than a rigid crop rotation because crops are only sown under optimal conditions, whereas rigid systems are not necessarily sown in the best conditions available.
Crop rotations also affect the timing and length of when a field is subject to fallow. This is very important because depending on a particular region's climate, a field could be the most vulnerable to erosion when it is under fallow. Efficient fallow management is an essential part of reducing erosion in a crop rotation system. Zero tillage is a fundamental management practice that promotes crop stubble retention under longer unplanned fallows when crops cannot be planted. Such management practices that succeed in retaining suitable soil cover in areas under fallow will ultimately reduce soil loss. In a recent study that lasted a decade, it was found that a common winter cover crop after potato harvest such as fall rye can reduce soil run-off by as much as 43%, and this is typically the most nutritional soil.
Biodiversity | Crop rotation | Wikipedia | 404 | 46470 | https://en.wikipedia.org/wiki/Crop%20rotation | Technology | Soil and soil management | null |
Increasing the biodiversity of crops has beneficial effects on the surrounding ecosystem and can host a greater diversity of fauna, insects, and beneficial microorganisms in the soil as found by McDaniel et al 2014 and Lori et al 2017. Some studies point to increased nutrient availability from crop rotation under organic systems compared to conventional practices as organic practices are less likely to inhibit of beneficial microbes in soil organic matter, such as arbuscular mycorrhizae, which increase nutrient uptake in plants. Increasing biodiversity also increases the resilience of agro-ecological systems.
Farm productivity
Crop rotation contributes to increased yields through improved soil nutrition. By requiring planting and harvesting of different crops at different times, more land can be farmed with the same amount of machinery and labour.
Risk management
Different crops in the rotation can reduce the risks of adverse weather for the individual farmer.
Challenges
While crop rotation requires a great deal of planning, crop choice must respond to a number of fixed conditions (soil type, topography, climate, and irrigation) in addition to conditions that may change dramatically from year to the next (weather, market, labor supply). In this way, it is unwise to plan crops years in advance. Improper implementation of a crop rotation plan may lead to imbalances in the soil nutrient composition or a buildup of pathogens affecting a critical crop. The consequences of faulty rotation may take years to become apparent even to experienced soil scientists and can take just as long to correct.
Many challenges exist within the practices associated with crop rotation. For example, green manure from legumes can lead to an invasion of snails or slugs and the decay from green manure can occasionally suppress the growth of other crops. | Crop rotation | Wikipedia | 345 | 46470 | https://en.wikipedia.org/wiki/Crop%20rotation | Technology | Soil and soil management | null |
The oat (Avena sativa), sometimes called the common oat, is a species of cereal grain grown for its seed, which is known by the same name (usually in the plural). Oats appear to have been domesticated as a secondary crop, as their seeds resembled those of other cereals closely enough for them to be included by early cultivators. Oats tolerate cold winters less well than cereals such as wheat, barley, and rye, but need less summer heat and more rain, making them important in areas such as Northwest Europe that have cool wet summers. They can tolerate low-nutrient and acid soils. Oats grow thickly and vigorously, allowing them to outcompete many weeds, and compared to other cereals are relatively free from diseases.
Oats are used for human consumption as oatmeal, including as steel cut oats or rolled oats. Global production is dominated by Canada and Russia; global trade is a small part of production, most of the grain being consumed within the producing countries. Oats are a nutrient-rich food associated with lower blood cholesterol and reduced risk of human heart disease when consumed regularly. One of the most common uses of oats is as livestock feed; the crop can also be grown as groundcover and ploughed in as a green manure.
Origins
Phylogeny
Phylogenetic analysis using molecular DNA and morphological evidence places the oat genus Avena in the Pooideae subfamily. That subfamily includes the cereals wheat, barley, and rye; they are in the Triticeae tribe, while Avena is in the Poeae, along with grasses such as Briza and Agrostis. The wild ancestor of Avena sativa and the closely related minor crop – A. byzantina – is A. sterilis, a naturally hexaploid wild oat, one that has its DNA in six sets of chromosomes. Genetic evidence shows that the ancestral forms of A. sterilis grew in the Fertile Crescent of the Near East. | Oat | Wikipedia | 418 | 46573 | https://en.wikipedia.org/wiki/Oat | Biology and health sciences | Poales | null |
Analysis of maternal lineages of 25 Avena species using chloroplast and mitochondrial DNA showed that A. sativa hexaploid genome derives from three diploid oat species (each with two sets of chromosomes); the sets are dubbed A, B, C, and D. The diploid species are the CC A. ventricosa, the AA A. canariensis, and the AA A. longiglumis, along with two tetraploid oats (each with four sets), namely the AACC A. insularis and the AABB A. agadiriana. Tetraploids were formed as much as 10.6 mya, and hexaploids as much as 7.4 mya.
Domestication
Genomic study suggests that the hulled variety and the naked variety A. sativa var. nuda diverged around 51,200 years ago, long before domestication. This implies that the two varieties were domesticated independently.
Oats are thought to have emerged as a secondary crop. This means that they are derived from what was considered a weed of the primary cereal domesticates such as wheat. They survived as a Vavilovian mimic by having grains that Neolithic people found hard to distinguish from the primary crop.
Oats were cultivated for some thousands of years before they were domesticated. A granary from the Pre-Pottery Neolithic, about 11,400 to 11,200 years ago in the Jordan Valley in the Middle East contained a large number of wild oat grains (120,000 seeds of A. sterilis). The find implies intentional cultivation. Domesticated oat grains first appear in the archaeological record in Europe around 3000 years ago.
Description | Oat | Wikipedia | 352 | 46573 | https://en.wikipedia.org/wiki/Oat | Biology and health sciences | Poales | null |
The oat is a tall stout grass, a member of the family Poaceae; it can grow to a height of . The leaves are long, narrow, and pointed, and grow upwards; they can be some in length, and around in width. At the top of the stem, the plant branches into a loose cluster or panicle of spikelets. These contain the wind-pollinated flowers, which mature into the oat seeds or grains. Botanically the grain is a caryopsis, as the wall of the fruit is fused on to the actual seed. Like other cereal grains, the caryopsis contains the outer husk or bran, the starchy food store or endosperm which occupies most of the seed, and the protein-rich germ which if planted in soil can grow into a new plant.
Agronomy
Cultivation
Oats are annual plants best grown in temperate regions. They tolerate cold winters less well than wheat, rye, or barley; they are harmed by sustained cold below . They have a lower summer heat requirement and greater tolerance of (and need for) rain than the other cereals mentioned, so they are particularly important in areas with cool, wet summers, such as Northwest Europe.
Oats can grow in most fertile, drained soils, being tolerant of a wide variety of soil types. Although better yields are achieved at a soil pH of 5.3 to 5.7, oats can tolerate soils with a pH as low as 4.5. They are better able to grow in low-nutrient soils than wheat or maize, but generally are less tolerant of high soil salinity than other cereals. Traditionally, US farmers grew oats alongside red clover and alfalfa, which fixed nitrogen and provided animal forage. With less use of horses and more use of fertilizers, growth of these crops in the US declined. For example, the state of Iowa led US oat production until 1989, but has largely switched to maize and soybeans.
Weeds, pests, and diseases
Oats can outcompete many weeds, as they grow thickly (with many leafy shoots) and vigorously, but are still subject to some broadleaf weeds. Control can be by herbicides, or by integrated pest management with measures such as sowing seed that is free of weeds. | Oat | Wikipedia | 471 | 46573 | https://en.wikipedia.org/wiki/Oat | Biology and health sciences | Poales | null |
Oats are relatively free from diseases. Nonetheless, they suffer from some leaf diseases, such as stem rust (Puccinia graminis f. sp. avenae) and crown rust (P. coronata var. avenae).
Crown rust infection can greatly reduce photosynthesis and overall physiological activities of oat leaves, thereby reducing growth and crop yield.
Processing
Harvested oats go through multiple stages of milling. The first stage is cleaning, to remove seeds of other plants, stones and any other extraneous materials. Next is dehulling to remove the indigestible bran, leaving the seed or "groat". Heating denatures enzymes in the seed that would make it go sour or rancid; the grain is then dried to minimise the risk of spoilage by bacteria and fungi. There may follow numerous stages of cutting or grinding the grain, depending on which sort of product is required. For oatmeal (oat flour), the grain is ground to a specified fineness. For home use such as making porridge, oats are often rolled flat to make them quicker to cook.
Oat flour can be ground for small scale use by pulsing rolled oats or old-fashioned (not quick) oats in a food processor or spice mill.
Production and trade
In 2022, global production of oats was 26 million tonnes, led by Canada with 20% of the total and Russia with 17% (table). This compares to over 100 million tonnes for wheat, for example. Global trade represents a modest percentage of production, less than 10%, most of the grain being consumed within producing countries. The main exporter is Canada, followed by Sweden and Finland; the US is the main importer.
Oats futures are traded in US dollars in quantities of 5000 bushels on the Chicago Board of Trade and have delivery dates in March, May, July, September, and December.
Genomics
Genome | Oat | Wikipedia | 396 | 46573 | https://en.wikipedia.org/wiki/Oat | Biology and health sciences | Poales | null |
Avena sativa is an allohexaploid species with three ancestral genomes (2n=6x=42; AACCDD). As a result, the genome is large (12.6 Gb, 1C-value=12.85) and complex. Cultivated hexaploid oat has a unique mosaic chromosome architecture that is the result of numerous translocations between the three subgenomes. These translocations may cause breeding barriers and incompatibilities when crossing varieties with different chromosomal architecture. Hence, oat breeding and the crossing of desired traits has been hampered by the lack of a reference genome assembly. In May 2022, a fully annotated reference genome sequence of Avena sativa was reported. The AA subgenome is presumed to be derived from Avena longiglumis and the CCDD from the tetraploid Avena insularis.
Genetics and breeding
Species of Avena can hybridize, and genes introgressed (brought in) from other "A" genome species have contributed many valuable traits, like resistance to oat crown rust. is one such trait, introgressed from A. sterilis CAV 1979, conferring all stage resistance (ASR) against Pca.
It is possible to hybridize oats with grasses in other genera, allowing plant breeders the ready introgression of traits. In contrast to wheat, oats sometimes retain chromosomes from maize or pearl millet after such crosses. These wide crosses are typically made to generate doubled haploid breeding material; the rapid loss of the alien chromosomes from the unrelated pollen donor results in a plant with only a single set of chromosomes (a haploid).
The addition lines with alien chromosomes can be used as a source for novel traits in oats. For example, research on oat-maize-addition lines has been used to map genes involved in C4 photosynthesis. To obtain Mendelian inheritance of these novel traits, radiation hybrid lines have been established, where maize chromosome segments have been introgressed into the oat genome. This potentially transfers thousands of genes from a species that is distantly related, but is not considered a GMO technique.
A 2013 study applied simple sequence repeat and found five major groupings, namely commercial cultivars and four landrace groups.
Nutritive value
Nutrients | Oat | Wikipedia | 484 | 46573 | https://en.wikipedia.org/wiki/Oat | Biology and health sciences | Poales | null |
Uncooked oats are 66% carbohydrates, including 11% dietary fiber and 4% beta-glucans, 7% fat, 17% protein, and 8% water (table). In a reference serving of , oats provide and are a rich source (20% or more of the Daily Value, DV) of protein (34% DV), dietary fiber (44% DV), several B vitamins, and numerous dietary minerals, especially manganese (213% DV) (table).
Health effects
Regular consumption of oat products lowers blood levels of low-density lipoprotein and total cholesterol, reducing the risk of cardiovascular disease. The beneficial effect of oat consumption on lowering blood lipids is attributed to oat beta-glucan. Oat consumption can help to reduce body mass index in obese people.
The United States Food and Drug Administration allows companies to make health claims on labels of food products that contain soluble fiber from whole oats, as long as the food provides 0.75 grams of soluble fiber per serving.
Uses
As food
When used in foods, oats are most commonly rolled or crushed into oatmeal or ground into fine oat flour. Oatmeal is chiefly eaten as porridge, but may also be used in a variety of baked goods, such as oatcakes (which may be made with coarse steel-cut oats for a rougher texture), oatmeal cookies and oat bread. Oats are an ingredient in many cold cereals, in particular muesli and granola; the Quaker Oats Company introduced instant oatmeal in 1966. Oats are also used to produce milk substitutes ("oat milk"). the oat milk market became the second-largest among plant milks in the United States, following almond milk, but exceeding the sales of soy milk. As a mainstay of West Wales for centuries, until changes in farming practices in the 1960s, oats were used in many traditional Welsh dishes, including laverbread, a Welsh breakfast, and "cockles and eggs" served with oatbread. | Oat | Wikipedia | 446 | 46573 | https://en.wikipedia.org/wiki/Oat | Biology and health sciences | Poales | null |
In Britain, oats are sometimes used for brewing beer, such as oatmeal stout where a percentage of oats, often 30%, is added to the barley for the wort. Oatmeal caudle, made of ale and oatmeal with spices, was a traditional British drink and a favourite of Oliver Cromwell.
Animal feed
Oats are commonly used as feed for horses when extra carbohydrates and the subsequent boost in energy are required. The oat hull may be crushed ("rolled" or "crimped") to make them easier to digest, or may be fed whole. They may be given alone or as part of a blended food pellet. Cattle are also fed oats, either whole or ground into a coarse flour using a roller mill, burr mill, or hammermill. Oat forage is commonly used to feed all kinds of ruminants, as pasture, straw, hay or silage.
Ground cover
Winter oats may be grown as an off-season groundcover and ploughed under in the spring as a green fertilizer, or harvested in early summer. They also can be used for pasture; they can be grazed a while, then allowed to head out for grain production, or grazed continuously until other pastures are ready.
Other uses
Oat straw is used as animal bedding; it absorbs liquids better than wheat straw. The straw can be used for making corn dollies, small decorative woven figures. Tied in a muslin bag, oat straw has been used to soften bath water.
Celiac disease
Celiac (or coeliac) disease is a permanent autoimmune disease triggered by gluten proteins. It almost always occurs in genetically predisposed people, having a prevalence of about 1% in the developed world. Oat products are frequently contaminated by other gluten-containing grains, mainly wheat and barley, requiring caution in the use of oats if people are sensitive to the gluten in those grains. For example, oat bread often contains only a small proportion of oats alongside wheat or other cereals. Use of pure oats in a gluten-free diet offers improved nutritional value, but remains controversial because a small proportion of people with celiac disease react to pure oats.
In human culture
In his 1755 Dictionary of the English Language, Samuel Johnson defined oats as "A grain, which in England is generally given to horses, but in Scotland supports the people." | Oat | Wikipedia | 512 | 46573 | https://en.wikipedia.org/wiki/Oat | Biology and health sciences | Poales | null |
"Oats and Beans and Barley Grow" is the first line of a traditional folksong (1380 in the Roud Folk Song Index), recorded in different forms from 1870. Similar songs are recorded from France, Canada, Belgium, Sweden, and Italy.
In English, oats are associated with sexual intercourse, as in the idioms "sowing one's (wild) oats", meaning having many sexual partners in one's youth, and "getting your oats", meaning having sex regularly. | Oat | Wikipedia | 106 | 46573 | https://en.wikipedia.org/wiki/Oat | Biology and health sciences | Poales | null |
Rye (Secale cereale) is a grass grown extensively as a grain, a cover crop and a forage crop. It is grown principally in an area from Eastern and Northern Europe into Russia. It is much more tolerant of cold weather and poor soil than other cereals, making it useful in those regions; its vigorous growth suppresses weeds and provides abundant forage for animals early in the year. It is a member of the wheat tribe (Triticeae) which includes the cereals wheat and barley. Rye grain is used for bread, beer, rye whiskey, and animal fodder. In Scandinavia, rye was a staple food in the Middle Ages, and rye crispbread remains a popular food in the region. Europe produces around half of the world's rye; relatively little is traded between countries. A wheat-rye hybrid, triticale, combines the qualities of the two parent crops and is produced in large quantities worldwide. In European folklore, the ("rye wolf") is a carnivorous corn demon or .
Origins
The rye genus Secale is in the grass tribe Triticeae, which contains other cereals such as barley (Hordeum) and wheat (Triticum).
The generic name Secale, related to Italian and French meaning "rye", is of unknown origin but may derive from a Balkan language. The English name rye derives from Old English , related to Dutch , German , and Russian , again all with the same meaning.
Rye is one of several cereals that grow wild in the Levant, central and eastern Turkey and adjacent areas. Evidence uncovered at the Epipalaeolithic site of Tell Abu Hureyra in the Euphrates valley of northern Syria suggests that rye was among the first cereal crops to be systematically cultivated, around 13,000 years ago. However, that claim remains controversial; critics point to inconsistencies in the radiocarbon dates, and identifications based solely on grain, rather than on chaff.
Domesticated rye occurs in small quantities at a number of Neolithic sites in Asia Minor (Anatolia, now Turkey), such as the Pre-Pottery Neolithic B Can Hasan III near Çatalhöyük, but is otherwise absent from the archaeological record until the Bronze Age of central Europe, c. 1800–1500 BCE. | Rye | Wikipedia | 465 | 46574 | https://en.wikipedia.org/wiki/Rye | Biology and health sciences | Poales | null |
It is likely that rye was brought westwards from Asia Minor as a secondary crop, meaning that it was a minor admixture in wheat as a result of Vavilovian mimicry, and was only later cultivated in its own right. Archeological evidence of this grain has been found in Roman contexts along the Rhine and the Danube and in Ireland and Britain. The Roman naturalist Pliny the Elder was dismissive of a grain that may have been rye, writing that it "is a very poor food and only serves to avert starvation". He said it was mixed with spelt "to mitigate its bitter taste, and even then is most unpleasant to the stomach".
Description
Rye is a tall grass grown for its seeds; it can be an annual or a biennial. Depending on environmental conditions and variety it reaches in height. Its leaves are blue-green, long, and pointed. The seeds are carried in a curved head or spike some long. The head is composed of many spikelets, each of which holds two small flowers; the spikelets alternate left and right up the head.
Cultivation
Since the Middle Ages, people have cultivated rye widely in Central and Eastern Europe. It serves as the main bread cereal in most areas east of the France–Germany border and north of Hungary. In Southern Europe, it was cultivated on marginal lands.
Rye grows well in much poorer soils than those necessary for most cereal grains. Thus, it is an especially valuable crop in regions where the soil has sand or peat. Rye plants withstand cold better than other small grains, surviving snow cover that would kill winter wheat. Winter rye is the most popular: it is planted and begins to grow in autumn. In spring, the plants develop rapidly. This allows it to provide spring grazing, at a time when spring-planted wheat has only just germinated.
The physical properties of rye affect attributes of the final food product such as seed size, surface area, and porosity. The surface area of the seed directly correlates to the drying and heat transfer time. Smaller seeds have increased heat transfer, which leads to lower drying time. Seeds with lower porosity lose water more slowly during the process of drying. | Rye | Wikipedia | 442 | 46574 | https://en.wikipedia.org/wiki/Rye | Biology and health sciences | Poales | null |
Rye is harvested like wheat with a combine harvester, which cuts the plants, threshes and winnows the grain, and releases the straw to the field where it is later pressed into bales or left as soil amendment. The resultant grain is stored in local silos or transported to regional grain elevators and combined with other lots for storage and distant shipment. Before the era of mechanised agriculture, rye harvesting was a manual task performed with scythes or sickles.
Agroecology
Winter rye is any breed of rye planted in the autumn to provide ground cover for the winter. It grows during warmer days of the winter when sunlight temporarily warms the plant above freezing, even while there is general snow cover. It can be used as a cover crop to prevent the growth of winter-hardy weeds.
Rye grows better than any other cereal in heavy clay and light sandy soil, and infertile or drought-affected soils. It can tolerate pH between 4.5 and 8.0, but soils having pH 5.0 to 7.0 are best suited for rye cultivation. Rye grows best in fertile, well-drained loam or clay-loam soils. As for temperature, the crop can thrive in subzero environments, assisted by the production of antifreeze polypeptides (different from those produced by some fish and insects) by the leaves of winter rye.
Rye is a common, unwanted invader of winter wheat fields. If allowed to grow and mature, it may cause substantially reduced prices (docking) for harvested wheat.
Pests and diseases
Pests including the nematode Ditylenchus dipsaci and a variety of herbivorous insects can seriously affect plant health.
Rye is highly susceptible to the ergot fungus. Consumption of ergot-infected rye by humans and animals results in ergotism, which causes convulsions, miscarriage, necrosis of digits, hallucinations and death. Historically, damp northern countries that depended on rye as a staple crop were subject to periodic epidemics. Modern grain-cleaning and milling methods have practically eliminated ergotism, but it remains a risk if food safety vigilance breaks down.
After an absence of 60 years, stem rust (Puccinia graminis f. sp. tritici) has returned to Europe in the 2020s. Areas affected include Germany, Russia (Western Siberia), Spain, and Sweden.
Production and consumption | Rye | Wikipedia | 497 | 46574 | https://en.wikipedia.org/wiki/Rye | Biology and health sciences | Poales | null |
Rye is grown primarily in Eastern, Central and Northern Europe. The main rye belt stretches from northern Germany through Poland, Ukraine, and eastwards into central and northern Russia. Rye is also grown in North America, in South America including Argentina, in Oceania (Australia and New Zealand), in Turkey, and in northern China. Production levels of rye have fallen since 1992 in most of the producing nations, ; for instance, production of rye in Russia fell from 13.9 metric tons in 1992 to 2.2 metric tons in 2022.
World trade of rye is low compared with other grains such as wheat. The total export of rye for 2016 was $186 million compared with $30.1 billion for wheat.
Poland consumes the most rye per person at per capita (2009), followed by the Nordic and Baltic countries. The EU in general is around per capita. The entire world only consumes per capita.
Nutritional value
Raw rye contains 11% water, 76% carbohydrates, 10% protein, and 2% fat (table). A reference amount of rye provides of food energy, and is a rich source (20% or more of the Daily Value, DV) of essential nutrients, including dietary fiber, B vitamins, such as thiamine and niacin (each at 25% DV), and several dietary minerals. Highest micronutrient contents are for manganese (130% DV) and phosphorus (27% DV) (table).
Health effects
According to Health Canada and the U.S. Food and Drug Administration, consuming at least per day of rye beta-glucan or per serving of soluble fiber can lower levels of blood cholesterol, a risk factor for cardiovascular diseases.
Eating whole-grain rye, as well as other high-fibre grains, improves regulation of blood sugar (i.e., reduces blood glucose response to a meal). Consuming breakfast cereals containing rye over weeks to months also improved cholesterol levels and glucose regulation.
Health concerns
Like wheat, barley, and their hybrids and derivatives, rye contains glutens and related prolamines, which makes it an unsuitable grain for consumption by people with gluten-related disorders, such as celiac disease, non-celiac gluten sensitivity, and wheat allergy, among others. Nevertheless, some wheat allergy patients can tolerate rye or barley.
Uses
Food and drink | Rye | Wikipedia | 492 | 46574 | https://en.wikipedia.org/wiki/Rye | Biology and health sciences | Poales | null |
Rye grain is refined into a flour high in gliadin but low in glutenin and rich in soluble fiber. Alkylresorcinols are phenolic lipids present in high amounts in the bran layer (e.g. pericarp, testa and aleurone layers) of wheat and rye (0.1–0.3% of dry weight). Rye bread, including pumpernickel, is made using rye flour and is a widely eaten food in Northern and Eastern Europe. In Scandinavia, rye is widely used to make crispbread (); in the Middle Ages it was a staple food in the region, and it remains popular in the 21st century.
Rye grain is used to make alcoholic drinks, such as rye whiskey and rye beer. The traditional cloudy and sweet-sour low-alcohol beverage kvass is fermented from rye bread or rye flour and malt.
Other uses
Rye is a useful forage crop in cool climates; it grows vigorously and provides plentiful fodder for grazing animals, or green manure to improve the soil. It forms a good cover crop in winter with its rapid growth and deep roots.
Rye straw is used as livestock bedding, despite the risk of ergot poisoning. It is used on a small scale to make crafts such as corn dollies. More recently it has found uses as a raw material for bioconversion to products such as the sweetener xylitol.
Rye flour is mixed with linseed oil and iron oxide to make traditional Falun red paint, widely used as a house paint in Sweden.
Production of hybrids
Plant breeders, starting in the 19th century in Germany and Scotland, but mainly from the 1950s, worked to develop a hybrid cereal with the best qualities of wheat and rye, now called triticale. Modern triticales are hexaploid with six sets of chromosomes; they are used to produce millions of tons of cereal annually. | Rye | Wikipedia | 399 | 46574 | https://en.wikipedia.org/wiki/Rye | Biology and health sciences | Poales | null |
Varieties of rye hold much genetic diversity, which can be used to improve other crops such as wheat. For example, the pollination abilities of wheat can be improved by the addition of the rye chromosome 4R; this increases the size of the wheat anther and the amount of pollen. The chromosome is the source of many crop disease resistance genes. Varieties such as Petkus, Insave, Amigo, and Imperial have donated 1R-originating resistance to wheat. AC Hazlet rye is a medium-sized winter rye with resistance to both lodging and shattering. Rye was the gene donor of Sr31 – a stem rust resistance gene – introgressed into wheat.
The characteristics of S. cereale have been combined with another perennial rye, S. montanum, to produce S. cereanum, which has the beneficial characteristics of each. The hybrid rye can be grown in harsh environments and on poor soil. It provides improved forage with digestible fiber and protein.
In human culture
In European folklore, the Roggenwolf ("rye wolf") is a carnivorous corn demon or Feldgeist, a field spirit shaped like a wolf. The Roggenwolf steals children and feeds on them. The last grain heads are often left at their place as a sacrifice for the agricultural spirits.
In contrast, the Roggenmuhme or Roggenmutter ("rye aunt" or "rye mother") is an anthropomorphic female corn demon with fiery fingers. Her bosoms are filled with tar and may end in tips of iron. Her bosoms are also long, and as such must be thrown over her shoulders when she runs. The Roggenmuhme is completely black or white, and in her hand she has a birch or whip from which lightning sparks. She can change herself into different animals, such as snakes, turtles, and frogs.
The classical scholar Carl A. P. Ruck writes that the Roggenmutter was believed to go through the fields, rustling like the wind, with a pack of rye wolves running after her. They spread ergot through the sheaves of harvested rye. According to Ruck, they then lured children into the fields to nurse on the infected grains "like the iron teats of the Roggenmutter". The enlarged reddish ergot-infected grains were known as Wulfzähne (wolf teeth). | Rye | Wikipedia | 497 | 46574 | https://en.wikipedia.org/wiki/Rye | Biology and health sciences | Poales | null |
The turnip or white turnip (Brassica rapa subsp. rapa) is a root vegetable commonly grown in temperate climates worldwide for its white, fleshy taproot. Small, tender varieties are grown for human consumption, while larger varieties are grown as feed for livestock. The name turnip used in many regions may also be used to refer to rutabaga (or neep or swede), which is a different but related vegetable.
Etymology
The origin of the word turnip is uncertain, though it is hypothesised that it could be a compound of turn as in turned/rounded on a lathe and neep, derived from Latin napus, the word for the plant. According to An Universal Etymological English Dictionary, turn refers to "round napus to distinguish it from the napi, which were generally long".
Description
The most common type of turnip is mostly white-skinned, apart from the upper , which protrude above the ground and are purple or red or greenish where the sun has hit. This above-ground part develops from stem tissue but is fused with the root. The interior flesh is entirely white. The root is roughly globular, from in diameter, and lacks side roots. Underneath, the taproot (the normal root below the swollen storage root) is thin and or more in length; it is often trimmed off before the vegetable is sold. The leaves grow directly from the above-ground shoulder of the root, with little or no visible crown or neck (as found in rutabagas).
Turnip leaves are sometimes eaten as "turnip greens" ("turnip tops" in the UK), and they resemble mustard greens (to which they are closely related) in flavor. Turnip greens are a common side dish in southeastern U.S. cooking, primarily during late fall and winter. Smaller leaves are preferred. Varieties of turnip grown specifically for their leaves resemble mustard greens and have small roots. These include rapini (broccoli rabe), bok choy, and Chinese cabbage. Similar to raw cabbage or radish, turnip leaves and roots have a pungent flavor that becomes milder after cooking.
Turnip roots weigh up to , although they are usually harvested when smaller. Size is partly a function of variety and partly a function of the length of time a turnip has grown.
Nutrition | Turnip | Wikipedia | 488 | 46576 | https://en.wikipedia.org/wiki/Turnip | Biology and health sciences | Brassicales | null |
Boiled green leaves of the turnip top ("turnip greens") provide of food energy in a reference serving of , and are 93% water, 4% carbohydrates, and 1% protein, with negligible fat (table). The boiled greens are a rich source (more than 20% of the Daily Value, DV) particularly of vitamin K (350% DV), with vitamin A, vitamin C, and folate also in significant content (30% DV or greater, table). Boiled turnip greens also contain substantial lutein (8440 micrograms per 100 g).
In a 100-gram reference amount, boiled turnip root supplies , with only vitamin C in a moderate amount (14% DV). Other micronutrients in boiled turnip are in low or negligible content (table). Boiled turnip is 94% water, 5% carbohydrates, and 1% protein, with negligible fat.
History
Wild forms of the turnip and its relatives, the mustards and radishes, are found over western Asia and Europe. Starting as early as 2000 BCE, related oilseed subspecies of Brassica rapa like oleifera may have been domesticated several times from the Mediterranean to India, though these are not the same turnips cultivated for its roots. Previous estimates of domestication dates are limited to linguistic analyses of plant names.
Edible turnips were first domesticated in Central Asia several thousand years ago, supported by genetic studies of both wild and domesticated varieties showing Central Asian varieties are the most genetically diverse crops. Ancient literary references to turnips in Central Asia, and the existence of words for 'turnip' in ancestral languages of the region, also support the turnip as the original domesticated form of Brassica rapa subsp. rapa. It later spread to Europe and East Asia with farmers in both areas later selecting for larger leaves; it subsequently became an important food in the Hellenistic and Roman world. The turnip spread to China, and reached Japan by 700 CE. | Turnip | Wikipedia | 428 | 46576 | https://en.wikipedia.org/wiki/Turnip | Biology and health sciences | Brassicales | null |
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