Nematodes in theMcMurdo Dry Valleys ofsouthern Victoria Land

DIANA W. FRECKMAN

Department of NematologyUniversity of California

Riverside, California 92521

Ross A. VIRGINIA

Department of Biology andSystems Ecology Research Group

San Diego State UniversitySan Diego, California 92182

Nematodes are among the most numerous invertebrates indesert soils and have an important role in nutrient cycling ofdesert ecosystems. We have been studying the ecology andfunctional significance of nematodes in the antarctic polar de-sert. During 1990-1991, we sought to examine the distributionof nematodes and their relationship to soil microbial and soilphysical and chemical factors in the McMurdo Dry Valleys andto determine the response of soil nematodes to temperature,moisture, and carbon augmentation in a 1-year field experi-ment.

Distribution of netnatodes. The locations selected for study rep-resented a diversity of soil types and variations in soil moisture.Sites spanning the lengths of Taylor, Garwood, and Wrightvalleys and a site at Cape Royds, Ross Island were sampledduring January 1990. In 1991 the sites that were sampled werethe following:• Taylor Valley—Lake Hoare, Lake Fryxell (Site of Special Sci-

entific Interest number 12, Canada Glacier) and LinneaeusTerrace (Site of Special Scientific Interest number 19).

• Wright Valley—Meserve Glacier, Lake Vanda, Lake Bull; Bea-con Valley, Meirs Valley; and McKelvey Valley.

• Victoria Valley—Lake Vida, Upper Victoria Valley; Bull Pass;and Cape Bird.

Replication at each site varied from 8 to 30 samples. Soils werecollected using sterile techniques, returned to McMurdo, andsubsampled within 24 hours for nematodes and soil moisture.A paired soil subsample was returned to the United States forfurther chemical and biotic analyses. Nematodes, tardigrades,and rotifers were extracted by sugar centrifugation andcounted, and nematodes were identified to genus and placedin functional groups (Freckman 1982). Sugar centrifugation wasselected for nematode extraction based on efficiency tests ofalternative methods (e.g., Baermann funnel and modifications)at McMurdo.

Contrary to expectations based on previous literature, morethan 65 percent of McMurdo Dry Valley soils contained nema-todes. The distribution of soil nematodes in the McMurdo DryValleys was more patchy than in other desert soils; however,where nematodes occurred, the densities in the McMurdo DryValleys (up to 4,000 per kilogram dry soil) were comparable tonematode densities in other desert soils (Freckman and Man-kau 1986). Nematodes occurred in greater abundance in drysoils than did rotifers and tardigrades, which were generally

restricted to moist soils near meltstreams. The diversity (threegenera) and trophic structure of the nematode community inMcMurdo Dry Valley soils is less complex than in other deserts.In McMurdo Dry Valley soils, nematodes occupy two or threefunctional levels, bacterial-feeding (Scottnema lindsayae, Plectussp.) and omnivore/predaceous (Eudorylaimus sp.).

High densities of nematodes occurred in soils with a widerange of soil moisture, salinity, nitrogen, and carbon contents(table). As in other desert soils, the relationship between ne-matodes and soil properties appears to be complex. Soil mois-ture and other soil physical and chemical properties such astotal nitrogen, organic carbon, phosphate, and salinity, ana-lyzed from Year I, did not significantly correlate with nematodeabundance. This suggests that energy availability and dispersalmay be more important factors regulating nematode abun-dance.

Field manipulation experiment. We had hypothesized that waterand temperature controls the activity of nematodes in theMcMurdo Dry Valleys, and that the energy supply of the soilsystem determines the population density and species com-position of the nematode community. To examine environmen-tal and biotic factors limiting nematode numbers, in 1990, weestablished a field experiment with six treatments and five rep-licates at Lake Hoare, Taylor Valley, where we manipulated soilconditions. The six treatments included the following:• a control,• increased water,• increased water and additional carbon (0.1 molar sucrose),• increased soil temperature,• increased water and increased temperature, and• a combination treatment of increased water, increased tem-

perature, and additional carbon.Temperature was increased by placing 0.5-square-meter poly-carbonate plastic "mini-greenhouses" over the soil. There wereno differences in nematode densities and life stages among thedifferent treatment plots at the initial sampling prior to impos-ing the treatments.

Selected chemical properties forMcMurdo Dry Valley soils containing nematodes, 1990

Mini-Maxi-CoefficientSoil propertyUnitMean mummumvariation

Organic carbon 0.086 NDa0.52387Total nitrogenmilligrams0.044 0.0060.347109

per gramAmmoniummilligrams1.17ND9.31112(NH4)per kilogramNitrate (NO3 )milligrams6.260.03102.0255

per kilogramPhosphatemilligrams1.170.018.92118(PO4 )per kilogrampH 8.475.559.988.1Electricaldeci Siemens 0.290.024.11223conductivityper meterNematodesLog (N+1)2.431.033.8031.1per kilogramof dry soil

a ND denotes no data.

1991 REVIEW 233

In January 1991, we resampled the soil using sterile tech-niques. Soil temperatures were significantly higher inside thechambers. Total densities of Scottnema, a bacterial-feeding ne-matode, were significantly greater on all treatments after 1 year,whereas the densities of the larger omnivore/predator, Eudory-laimus, were unchanged. The most significant effect of treat-ments was noted with the combination treatment of increasedtemperature plus carbon plus water where the densities ofScottnema males increased significantly over the control. Thismay indicate that Scottnema, a dominant genus endemic to theMcMurdo Dry Valleys is a sensitive indicator of soil environ-mental change.

This work was supported by National Science Foundationgrants DPP 88-18049 and DPP 89-14655. The authors acknowl-edge the contributions of their technical assistant during the1990 and 1991 seasons, John T Freckman.

References

Freckman, D.W 1982. Parameters of the nematode contribution to eco-systems. In D.W Freckman (Ed.), Nematodes in soil ecosystems. Austin:University of Texas Press.

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

Microorganisms entrappedin glacial ice

CATHARINE CATRANIS and WILLIAM T. STARMER

Department of BiologySyracuse University

Syracuse, New York 13244

We have been interested in reviving ancient microorganismsentrapped in glacial ice. These organisms have potential for usein studies on the mode and tempo of evolution. Our work hasbeen in two phases: first, to develop techniques for avoidingrecent external contamination and, second, to use these tech-niques to isolate microbes from ice cores obtained from glaciersin Greenland.

Protocol for isolating microorganism from ice. There are two majorproblems associated with recovering microorganisms from gla-cial ice. The first is to ensure that recent contaminants intro-duced during drilling, handling, and transportation are de-tected and avoided. The second is to find rare organismswithout damaging or killing them with the techniques used toeliminate the recent contaminants.

Experiments with artificially manufactured ice-core sectionsshowed that liquid sterilants such as sodium hypochlorite, andethanol were either partially effective for exterior sterilizationor resulted in considerable death for microorganisms found inthe interior. We thus abandoned the use of liquids as a meansof eliminating exterior contaminants. The procedure we devel-oped employs ultraviolet sterilization of the ends of the ice corefollowed by aseptic mechanical extraction of an interior core ina laminar flow hood at -20 °C. This results in an intact hollowouter (contaminated) piece and a solid interior piece (containingorganisms of interest). Extraction is accomplished by wrappingthe core with black paper and holding the paper in place withaluminum foil leaving 4-5 millimeters of ice on each end totallyexposed. This wrapped core is placed on a plastic petri dishand the exposed end pieces are irradiated with 28,620 joulesper square meter of ultraviolet light. The incident beams ofultraviolet light are perpendicular to long axis of the ice coresection to minimize ultraviolet exposure to the interior ice. The

dosage is in excess of what is necessary to provide a sterilesurface at both ends of the ice. This subsection of ice is placedinto a sterilized vise for the aseptic, mechanical extraction ofan inner core. From one of the sterile ends three to four 4millimeter holes are drilled aseptically through the ice (parallelto the long axis) exiting at the other sterile end. A sterile sawblade is inserted into a hole and an interior piece cut out bysawing from hole to hole. This inner piece is aseptically re-moved. This method results in a 30-70 percent recovery (byvolume) of noncontaminated ice from the original core.

Melting is accomplished by moving the pieces into anotherlaminar flow hood at 25 °C. Meltwater is collected into chemi-cally clean, sterile 1-liter Erlenmeyer flasks. The unfilteredmeltwater is used as a source for plating and inoculation of 10different culture media (petri dishes and broth tubes). The re-maining meltwater is filtered (millipore, 0.45 micrometers) un-der low vacuum pressure (30-50 millimeters of mercury). Thefilter paper is placed on a petri dish containing malt extractagar (a complete medium for the growth of fungi). All inocu-lated media, broth tubes and petri dishes with filters are in-cubated at 8 CC and inspected for growth of microorganisms at1, 3, and 6 weeks. The petri dishes and tubes are then movedto a 15 °C growth chamber for 2 weeks, followed by 1 week at20 °C. Media for the cultivation of algae are incubated underconstant light (full spectrum, 50-watt bulb at 8 °C).

Microbes isolated from glacial ice in Greenland. To date, 12 coresections from GISP2 (cores B and D), Dye-3 1971 and Dye-31979 have been melted. Microorganisms were recovered fromall sections of ice we have studied (tables 1 and 2). Isolatespresent on the most recently inoculated plates have not beenidentified as yet. Table 1 summarizes the number of uniquespecies recovered from each subsection. Table 2 lists the speciesrecovered from each section. Species present in more than onesubsection of the same section are indicated by an asterisk(table 2). Except for nonsporulating fungi, most of the filamen-tous fungi have been identified to genus and several to species.The identification of yeasts, bacteria, algae, and remaining fila-mentous fungi is in progress.

Discussion. The results show that it is possible to obtain avariety of microorganisms from the interior of ice cores. It isalso encouraging that some taxa were recovered from morethan one section and depth and thus multiple isolation of thesame taxon of progressively older age is feasible. The isolatesfrom the interior core and exterior shell basically fall into two

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