Terrestrial biology

Depth distribution of soil nematodes inTaylor Valley, Antarctica

LAURA E. POWERS and DIANA W. FRECKMAN, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins,Colorado 80523

Ross A. VIRGINIA, Environmental Studies Program, Dartmouth College, Hanover, New Hampshire 03755

The organisms that live in the seemingly barren soils of theantarctic dry valleys are subject to some of the most

extreme environmental conditions on Earth, including desic-cation, freezing, high salinity, and general heterogeneity of thechemical and physical aspects of the soils in which they exist(Campbell and Claridge 1987). These factors likely contributeto their distribution on both a micro- and macrohabitat scale.

Six genera and 11 species of nematodes have beendescribed from soils on continental Antarctica (Maslen 1979).Studies by Freckman and Virginia (1991) indicate that themicrobial feeding Scottnema lindsayae (Timm 1971) and the

Nematodes kg dry soil

2505007501000

00.010.020.030.040.05

Soil moisture (g/g)Nematodes per kilogram (kg- 1 ) of dry soil and soil moisture(gram/gram) at four depths on the north shore of Lake Hoare, TaylorValley, Antarctica.

omnivore/ predator Eudorylaimus antarcticus (Steiner 1916)(Yeates 1970) are the dominant nematodes in the dry valleysof Victoria Land. In temperate regions of the world, nema-todes—as herbivores—are an important component of thesoil food web aiding in decomposition processes and servingas a food source to other soil organisms (Yeates and Coleman1982, pp. 55-80).

Previous studies of nematodes in the antarctic dry valleyshave been restricted primarily to taxonomic identification(Timm 1971; Yeates 1970) or geographic distribution surveys(Freckman and Virginia 1991; Wharton and Brown 1989);however, information on nematode distribution with soildepth is important to design ecologically relevant samplingplans to study the ecology of nematodes in these soils and tointerpret results for determining the nematode contributionsto the sustainability of the dry valley ecosystem.

To examine the depth distribution of nematode commu -nities, we sampled sites on the north shore of Lake Hoare inTaylor Valley, Antarctica (77 038'S 162 053'E), in austral sum-mer 1993-1994. The sites chosen for sampling possessed thebroad geomorphic features characteristic of the landscape ofthe polar deserts of Victoria Land, with distinctively patternedground (polygons) and a disturbed, weathered regolith. Sam-ples were taken at four depth increments: 0-2.5 centimeters(cm), 2.5-5.0 cm, 5.0-10.0 cm, and 10.0-20.0 cm. Soils werecollected using sterile techniques, samples were returned toMcMurdo Station, and nematodes were extracted from thesamples within 48 hours (Freckman and Virginia 1993). Allnematodes extracted from the soils were identified to genusand enumerated. The soil moisture content of each samplewas determined by standard gravimetric method(weight/weight) at the time of nematode extractions.

Nematodes were present in all samples collected. Nema-tode populations were not related to soil moisture, whichincreased slightly with depth (figure). Total numbers ofnematodes were greatest at the 2.5-5.0-cm depth incrementon the north shore (figure).

The nematode community on the north side of LakeHoare consisted of two genera: the omnivore/ predator Eudo-rylaimus antarcticus and the microbial feeding nematodeScottnema lindsayae. These two genera showed different dis-

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447.3±205.9800.7±175.7640.9±148.1180.5±68.3

tributions as a function of soil depth. Scottnema populationsin the 2.5-10.0-cm range on the north side of the lake weregreater than those in the 10.0-20.0-cm soil depth increment(table), whereas Eudorylaimus was found primarily closer tothe surface, with a greater number found at the 2.5-5.0-cmdepth than in the 10.0-20.0-cm range (table).

Previous studies have found nematodes to be widely dis-tributed in the dry valleys (Freckman and Virginia 1990).Unlike soils from other ecosystems, however, a notable per-centage (34 percent) of soils sampled from dry valley loca-tions lack extractable nematodes (Freckman and Virginia1991), but where nematodes occur, peak densities are compa-rable to nematode densities in other desert soils (Freckmanand Mankau 1986). For the soils that contain nematodes, thedistribution of these animals is likely governed by such factorsas energy availability and dispersal (Freckman and Virginia1991). Nematodes may become distributed at depths that areclose enough to the surface to benefit from organic inputs tothe soils but deep enough to avoid other environmentalextremes that may influence their survival.

We thank John Freckman, Ericha Courtright, andMengchi Ho for their assistance in sampling and laboratoryanalyses. We also acknowledge the logistic support of the

North shore0-2.5373.5±171.073.8±43.6

2.5-5.0676.3±175.1124.4±12.75.0-10.0607.2±147.633.7±14.1

10.0-20.0174.1±63.46.4±3.9

National Science Foundation McMurdo Station laboratorystaff and the VXE-6 and Royal New Zealand Air Force heli-copter crews. This research was supported by National Sci-ence Foundation grant OPP 91-20123 to D.W. Freckman andR.A. Virginia.

References

Campbell, I.B., and G.G.C. Claridge. 1987. Antarctica: Soils, weather-ing processes and environment. New York: Elsevier.

Freckman, D.W., and R. Mankau. 1986. Abundance, distribution, bio-mass and energetics of soil nematodes in a Northern MojaveDesert ecosystem. Pedobiologia, 29, 129-142.

Freckman, D.W., and R.A. Virginia. 1990. Nematode ecology of theMcMurdo Dry Valley ecosystem. Antarctic Journal of the U.S.,25(5), 229-230.

Freckman, D.W., and R.A. Virginia. 1991. Nematodes in the McMurdoDry Valleys of southern Victoria Land. Antarctic Journal of theU.S., 26(5), 233-234.

Freckman, D.W., and R.A. Virginia. 1993. Extraction of nematodesfrom dry valley antarctic soils. Polar Biology, 13(7), 483-487.

Maslen, N.R. 1979. Additions to the nematode fauna of the antarcticregion with keys to taxa. British Antarctic Survey Bulletin, 49,207-229.

Timm, R.W. 1971. Antarctic soil and freshwater nematodes from theMcMurdo Sound region. Proceedings of the Helminthological Soci-

ety of Washington, 38(1), 42-52.Wharton, D.A., and I.M. Brown. 1989.

A survey of terrestrial nematodesfrom the McMurdo Sound region,Antarctica. New Zealand Journal ofZoology, 16,467-470.

1.nematodes' Yeates, G.W. 1970. Two terrestrialT

- nematodes from the McMurdoSound region Antarctica, with anote on Anaplectus arenicola Ku-lick, 1964. Journal of Helmintholo-gy, 44(1), 27-34.

25.9-1,155.6Yeates, G.W., and D.C. Coleman. 1982.519.9-1,479.0Role of nematodes in decomposi-409.6-1,044.0tion. In D.W. Freckman (Ed.),

17.2-342.4Nematodes in soil ecosystems.Austin: University of Texas Press.

Nematodes per kilogram of dry soil (mean ± standard deviation) at four depths onthe north shore of Lake Hoare, Taylor Valley, Antarctica

Limits of life and microbial extinction in the antarctic desertE. IMRE FRIEDMANN and ALEXANDER Y. DRUK, Polar Desert Research Center and Department of Biological Science, Florida State

University, Tallahassee, Florida 32306-2043CHRISTOPHER P. MCKAY, National Aeronautic and Space Administration-Ames Research Center, Space Sciences Division,

Mountain View, California 94035

Cryptoendolithic microorganisms under the surface ofrocks in the antarctic desert (Nienow and Friedmann

1993, pp. 343-412) live in an "absolute extreme" cold environ-ment (Friedmann 1993a, 1993b). Temperatures are far belowthe biologically optimal values, and the organisms exist nearthe limit of their physiological potential. Deterioration of theenvironment, such as a slow climate change, can upset the

delicate physiological equilibrium, and the result is death andextinction: in the high desert areas of the McMurdo Dry Val-leys ("Ross Desert"), a significant portion of the sandstonerock surfaces harbor fossil microbial communities.

It has been suggested that the cryptoendolithic microbialecosystem of the antarctic desert is a terrestrial model for thelast stages of life on early Mars (McKay et al. 1992). The study

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