Antarctica is one of the most physically and chemically extreme terrestrial environments to be inhabited by lifeforms.[1] The largest plants are mosses, and the largest animals that do not leave the continent are a few species of insects.
Although most of the continent is covered by glacialice sheets, ice-free areas comprising approximately 0.4% of the continental land mass are discontinuously distributed around the coastal margins.[1] TheMcMurdo Dry Valleys region ofAntarctica is apolar desert characterized by extremely low annual precipitation(<100 mm (3.9 in)) and an absence ofvascular plants andvertebrates; microbial activity dominates biological functioning.[2] Mean summer high and winter low temperatures in the dry valleys are−5 °C (23 °F) and −30 °C (−22 °F).[2] Because precipitation is both infrequent and low, seasonal water availability in hydrologically connected soils make areas adjacent to water bodies more hospitable relative to dry upland soils.[2] Polar ecosystems are particularly sensitive toclimate change, where small changes in temperature result in greater changes in localhydrology, dramatically affectingecosystem processes.[3]
Soils inAntarctica are nearly two-dimensional habitats, with most biological activity limited to the top four or five inches by the permanently frozen ground below.[4] Environments can be limiting due to soil properties such as unfavorable mineralogy,texture,structure,salts,pH, ormoisture relationships.[5] Visible sources oforganic matter are absent for most of continental Antarctica.[3]Dry Valley soil ecosystems are characterized by large variations in temperature and light regimes, steep chemical gradients and a high incidence ofsolar radiation with an elevatedultraviolet B (UVB) light component.[1] Dry Valley soils originate from weathering ofbedrock and glacialtills that consist ofgranites,sandstones,basalts andmetamorphic rocks.[1] Space within these rocks provide protection for microorganisms against some (but not all) of these conditions: i.e., protection fromwind scouring and surface mobility, a reduction in UV exposure, reduceddesiccation and enhanced water availability, and thermal buffering.[6] Half of the soils in the Dry Valleys have subsurface ice, either as buried massive ice or as ice-cemented soil (permafrost).[1] The permafrost layer is typically within 30 cm (12 in) of the soil surface.[1]
The harsh environment and low availability ofcarbon and water support a simplified community ofmosses,lichens, and mats ofgreen algae and red, orange, and blackcyanobacteria near lakes andephemeral streams.[4] Living among the mats arebacteria,yeasts,molds, and an array of microscopicinvertebrates that feed on microbes,algae, anddetritus:nematodes,protozoa,rotifers,tardigrades, and occasionally,mites andspringtails.[4] Even simpler communities exist in thearid soils that occupy the majority of the landscape.[3]
Microbes inAntarctica adapt to aridity the same way microbes in hot deserts do: when water becomes scarce, the organisms simply dry up, shut downmetabolic activity, and wait in acryptobiotic state until water again becomes available.[4] Microbes can also go dormant in a cryptobiotic state known asanhydrobiosis when they become dehydrated due to low water availability.[4] A more extreme survival method would be long term naturalcryopreservation. Samples ofpermafrost sediments aged 5–10 thousand to 2–3 million years old have been found to contain viable micromycete andbacterial cells.[7]
Algae is present in almost all ice-free areas and occurs insoils, asepiphytes onmosses, incyanobacterial mats and inplankton of lakes and ponds.[8] It is also possible to find algae associated with rocks or living in the thin film of melted water in the snow patches.[8] Presently there are over 300 algal taxa identified onAntarctica, withBacillariophyceae (Diatoms) andChlorophyta (Green algae) being the most widespread on Antarctica.[8] Diatoms are abundant in aquatic environments decreasing in number interrestrial habitats.[8] Chlorophyta are also important in mats in lakes and ponds but tend to increase their relative importance in terrestrial environments and especially in soils, where they are the densest algal group.[8]Xanthophyceae (Yellow-green algae) are an important component of theflora in soils of Antarctica.[8] Other algal groups (Dinophyta,Cryptophyta, andEuglenophyta) are mainly limited to freshwater communities of theDry Valleys.[8]
Algae species identified in recent research:[8][9]
Distribution ofarthropods is limited to areas of high soil moisture and/or access to water, such as streams, or snow meltwater.[8]
Carbon appears to be more important than moisture in defining good habitats fornematodes in theDry Valleys ofAntarctica.[4]Scottnema lindsayae, a microbial feeder and the most abundant and widely distributedmetazoaninvertebrate, often occurs as the solemetazoan species in theMcMurdo Dry Valleys.[3] It makes its living eatingbacteria andyeast out in the dry, salty soils that dominate the valleys.[4] All otherinvertebrate species are more abundant in moist or saturated soils wherealgae andmoss are more abundant.[3] Distribution of mostnematode species is correlated negatively with elevation (due to temperature and precipitation) andsalinity, and positively withsoil moisture,soil organic matter, and nutrient availability.[3]Eudorylaimus spp. is the second most abundantnematode, followed byPlectus murrayi who are the least abundantnematodes.[3]Plectus antarcticus eatsbacteria and prefers living inephemeral streams.[4] An average 2-pound bag ofdry valley soils contains approximately 700nematodes, while the more fertile soil found at higher latitudes on the continent may contain approximately 4,000nematodes.[4]
Nematode species identified in recent research:[3][4][8]
The three species listed below were found inmoss-dominated moist soils.[8]
Rotifer species identified in recent research:[8]
Tardigrade species identified in recent research:[8]
Typically, the highest numbers of culturedbacteria are from relatively moist coastal soils, compared with the small bacteria communities of dry inland soils.[8]Cyanobacteria are found in all types of aquatic habitats and often dominate the microbial biomass of streams and lake sediments.[8]Leptolyngbya frigida is dominant in benthic mats, and is frequently found in soils and as anepiphyte onmosses.[8]Nostoc commune can develop to sizes visible to the naked eye if supplied with a thin water film.[8] The genusGloeocapsa is one of the fewcryptoendolithic taxa with a high adaptation to extreme environmental conditions in rocks of theDry Valleys.[8]Actinomycetota such asArthrobacter spp.,Brevibacterium spp., andCorynebacterium spp. are prominent in the Dry Valleys.[1]Thermophilic bacteria have been isolated from thermally heated soils nearMt. Melbourne and Mt. Rittman in northernVictoria Land.[8] Bacteria genera found in both air samples and theAntarctic includeStaphylococcus,Bacillus,Corynebacterium,Micrococcus,Streptococcus,Neisseria, andPseudomonas.[7] Bacteria were also found living in the cold and dark in a lake buried a half-mile deep (0.80 km) under the ice inAntarctica.[10][11][12]
Bacteria species identified in recent research:[8]
Chaetomium gracile is frequently isolated from geothermally heated soil onMt. Melbourne in northernVictoria Land.[8] Fungi genera found in both air samples and theAntarctic includePenicillium,Aspergillus,Cladosporium,Alternaria,Aureobasidium,Botryotrichum,Botrytis,Geotrichum,Staphylotrichum,Paecilomyces, andRhizopus.[7]
Fungi species identified in recent research:[8][14]
Yeast species identified in recent research:[8]
The smallamoebae are of two types. The most abundant areAcanthamoeba andEchinamoeba.[8] The second group consists of monopodal, worm-like amoebae, thesubcylindricalHartmannella andSaccamoeba, and thelingulatePlatyamoeba stenopodia Page.[8]
Amoebae species identified in recent research:[8]
Flagellate species identified in recent research:[8]
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