Abstracts

HUMAN DISTURBANCE AND NEMATODE DECLINE IN ANTARCTIC DRY VALLEY SOIL.

Broos, E.J.1, D.H. Wall.1, R.A. Virginia2, J.N. Nkem1, L.E. Powers3, and B.J. Adams.41Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523, 2Environmental Studies Program, Dartmouth College, Hanover NH 03755, 3Department of Engineering, University of Wisconsin, Madison WI 53706, 4Microbiology and Molecular Biology Department, Brigham Young University, Provo UT 84602.

Abstract

The McMurdo Dry Valleys of Antarctica contain the simplest soil communities on earth but may be threatened by increasing human disturbance through tourism, scientific activity and climate change. Most human activity in the dry valleys consists of movement to sites by foot. In this study, over a period of eight years we examined the effect of heavy and light trampling (foot paths) on soil nematode communities. Nematode communities were sampled to 10 cm depth from soil in trampled areas and compared to communities in immediately adjacent undisturbed areas. In the last year of sampling the effect of trampling on nematode communities at varying soil depth (0 to 2.5 cm and 2.5 to 10 cm) was also investigated. Overall, total nematode abundance was lower in trampled areas than undisturbed areas (P<0.05). The effect was most significant in the last year of sampling when nematode abundance was ≤71% lower in trampled areas than undisturbed areas. Eudorylaimus antarcticus were ≤74% more abundant in areas with light trampling than heavy trampling (P<0.05). Over the eight year duration of the experiment nematode abundance was constant in the heavily trampled areas but fluctuated in the lightly trampled and undisturbed areas  (P<0.05). Differences in nematode communities between trampled and undisturbed areas were observed both in samples taken to 2.5 cm and to 10 cm depth but were more significant in the surface samples. These results indicate Antarctic soil nematode communities are sensitive to human disturbance by trampling and effects increase with duration of disturbance.

RESPONSE OF SOIL NEMATODES TO MOISTURE ADDITIONS FROM SNOW FENCES IN TAYLOR VALLEY, ANTARCTICA.

Nkem, J.N,1 D.H. Wall,1 R.A. Virginia,2 E.J. Broos1, J.E. Barett,2 and B.J. Adams3. A.N. Parsons.11Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523, 2Environmental Studies Program, Dartmouth College, Hanover, NH 03755, 3Microbiology and Molecular Biology, Brigham Young University Provo, UT 84602

Abstract

Taylor Valley is a polar desert with very low soil moisture content (~1%) and nematode diversity (3 species). Changes in soil moisture associated with climate variation may influence nematode populations over time. We erected snow fences 1 m high and 6 m long in two lake basins; Fryxell and Bonney, to evaluate soil nematode response to moisture addition. Soil samples were taken after snow melt at 0.91 m intervals to a distance 3.65 m from the snow fence in the austral summer of 2001, 2003, and 2004, and analyzed for nematode response and moisture content. Soil moisture differed over time and between the two basins (P<0.0001) but was not different between the sampling positions. Fryxell, had higher soil moisture than Bonney and a significant increase in soil moisture content in 2003 and 2004. Soil nematode abundance declined over time (P<0.0001) especially with increasing soil moisture (>2%) but species composition did not change. Abundance of the dominant species, Scottnemalindsayae declined (P<0.0001) while the abundance of Plectus antarcticus increased (P<0.0155) and Eudorylaimus antarcticus showed an increasing trend. Total nematode mortality increased over time mostly due to Scottnema lindsayae (P<0.0001), which responded negatively to soil moisture increases. Long-term supplements of moisture to soils as predicted with global change, could potentially change the community structure and population dynamics of soil nematodes in the dry valleys.

RATES OF MOLECULAR EVOLUTION IN ANTARCTIC AND TEMPERATE NEMATODES.

Bliss, T. J.,1 B. J. Adams,1 and U. Gozel.2

1Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84604, 2Entomology and Nematology Department, University of Florida, Gainesville, FL 32611.

Abstract

While it is well established that different species appear to evolve at different rates across evolutionary time, correlations between the rate of evolution and biological or ecological constraints are poorly understood. Nematodes from the Antarctic Dry Valleys have long generation times, but shorter periods of time to complete their life cycle compared to closely related species from temperate regions. Thus, we predict that Antarctic nematodes should evolve more slowly than sister taxa in warmer climates that are able to complete more generations over the same period of time. To test this hypothesis we sequenced ribosomal genes from Antarctic Nematodes and compared their rates of molecular evolution with sister taxa from more northerly distributions. Compared to other nematodes in the phylum Nematoda, Eudorylaimus antarcticus appears to evolve significantly slower than its counterparts. However, when the comparison is constrained to account for phylogenetic autocorrelation, evolutionary rate differences disappear. The extent to which these patterns hold up across the phylum may provide an understanding of the role of rates of molecular change in the mode and tempo of nematode evolution.

IDENTIFICATION OF TROPHIC RELATIONSHIPS FOR FREE-LIVING MICROBIVOROUS NEMATODES VIA DNA EXTRACTION, AMPLIFICATION, AND SEQUENCING OF NEMATODE GUT CONTENTS.

Winkler, Kyle A., and B. J. Adams.  Department of Microbiology and Molecular Biology, Brigham Young University, Provo, UT 84604.

Abstract

Species-specific food web relationships involving free-living microbivorous nematodes are not well established, yet critical to our understanding of their involvement in nutrient cycling and ecosystem function. Antarctic soil ecosystems are the simplest on earth and serve as a model system for exploring the role of biodiversity in ecosystem function. To establish which bacteria are involved in trophic relationships with Antarctic Dry Valley nematodes, we surface-sterilized nematodes and extracted their DNA, including bacterial DNA from the gut contents of the nematodes. From this bacterial DNA we PCR amplified the 16S gene and sequenced the product in order to determine the identity of the gut contents of the nematode. Given a broader sampling regimen, this approach can be used to establish food web relationships in more complex ecosystems.

SOIL CARBON DIOXIDE FLUX IN ANTARCTIC DRY VALLEY ECOSYSTEMS

Parsons A.N., J.E. Barrett, D.H. Wall, and R.A. Virginia. Ecosystems 7(3): 286-295 APR 2004

Abstract

The Antarctic dry valleys of southern Victoria Land are extreme desert environments where abiotic factors, such as temperature gradients, parent material, and soil water dynamics, may have a significant influence on soil carbon dioxide (CO2) flux. Previous measurements of soil respiration have demonstrated very low rates of CO2, efflux, barely above detection limits. We employed a modified infrared gas-analyzer system that enabled detection of smaller changes in CO2 concentration in the field than previously possible. We measured diel CO2 fluxes and monitored soil microclimate at three sites in Taylor Valley. Soil CO2 flux ranged from -0.1 to 0.15 mumol m(-2) s(-1). At two of the three sites, we detected a physically driven flux associated with diel variability in soil temperature. At these sites, CO2 uptake (negative flux) was associated with dropping soil temperatures, whereas CO, evolution (positive flux) was associated with increases in soil temperature. These observations are corroborated by laboratory experiments that suggest that CO2 flux is influenced by physically driven processes. We discuss four potential mechanisms that may contribute to physically driven gas exchange. Our results suggest there are strong interactions between biological and abiotic controls over soil CO2 flux in terrestrial ecosystems of the Antarctic dry valleys, and that the magnitude of either may dominate depending on the soil environment and biological activity.

DIVERSITY AND FUNCTION IN DISTURBED AND UN-DISTURBED HABITATS: A PERSPECTIVE FROM SOIL ECOLOGY.

Wall, D.H.  Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, USA

I will review disturbances and soil ecological responses from un-disturbed habitats as a basis for comparison to urban habitats. Soils in un-disturbed habitats form over long temporal scales as a result of climatic, geologic and anthropogenic legacies. Within these soils, a diversity of organisms evolved strategies to withstand or recover from disturbances. The response of these organisms to disturbance must be examined across multi- spatial and temporal scales because the scales at which organisms operate, regulate ecosystem processes, and provide ecosystem services can differ. Disturbances also vary by type (e.g. intensive agriculture vs no-till agriculture), temporal and spatial scales adding additional complexity. While there is little evidence to indicate soil species diversity in un-disturbed sites is directly related to ecosystem functioning, we know that species diversity decreases with habitat disturbance, leading to a dominance of the communities

by a few species. At the functional group level, particularly for earthworms and termites, disturbances leading to loss of taxa can have major effects on the provision of ecosystem services. Urban habitats, in contrast, can have higher soil biodiversity, carbon and trace gas flux than

un-disturbed soils, but the composition of the assemblages and ability to provide ecosystem services will operate at shorter spatial and temporal spatial scales. Above- and belowground biological systems are integrally linked and provide a framework for measuring ecosystem responses to disturbance in all soils.

BIODIVERSITY AND ECOSYSTEM FUNCTIONING IN TERRESTRIAL HABITATS OF ANTARCTICA.

Wall D.H. Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO, USA

Abstract

The ice-free terrestrial regions of Antarctica are among the simplest terrestrial ecosystems on earth, with low species richness and trophic complexity. As a result, relationships between biodiversity, ecological processes and the effect of global change are more apparent. Knowledge gained from study of Antarctic soil ecosystems can contribute to ecological questions on biodiversity and ecosystem functioning and current issues such as ecosystem and soil sustainability. Research on soil communities with low diversity provides an opportunity to elucidate relationships between species diversity and physical and chemical factors, and determine local to landscape patterns and relationships that are masked by the overwhelming complexity of biodiversity found in most terrestrial ecosystems. There appears to be heterogeneity in habitats and high and low productivity and foodweb complexity even within the Dry Valleys. Current evidence for the soils of Antarctica indicates that there is substantially greater abundance and diversity, mostly endemic, than previously thought. A range of species diversity occurs across the continent, with low species diversity determined by geophysical soil factors in extreme habitats and high soil diversity greatly influenced by biotic factors, such as predator - prey interactions. These habitats are integrally connected to marine and freshwater ecosystems, and to the atmosphere. Current work is examining the climatic and edaphic properties that underlie this range of productivity and diversity, and the sensitivity of ecosystems across this gradient to global change. How the terrestrial systems will respond to different global changes (e.g., climate change, invasive species) is needed information for conservation and monitoring and for comparison within and across the Antarctic.  The need for a soil experimental network will be discussed

Antarctic Research

Publications

Field Research Teams

Outreach

Links

Soil Inventory (.xls)

This material is based on work supported by the National Science Foundation under Grant No. NSF OPP 0229836. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.