Cape Hallett Soils and Microbes

Soil Biodiversity and Response to Climate Change: A Regional Comparison of Cape Hallett and Taylor Valley, Antarctica

Rocky ornithogenic soil on Seabee Hook.

 

Our objective is to understand how soil and climate factors control the biodiversity of Antarctic soil communities and in turn their role in ecosystem processes.  We will examine how soil organic matter from legacy and contemporary sources, moisture, and temperature interact to structure soil habitat suitability in Taylor Valley (a low biodiversity ecosystem) and Cape Hallett (a high biodiversity ecosystem).  Our research will have a field and laboratory component. In the field at both sites, we will sample along gradients of soil organic matter, salinity and moisture.  In the laboratory, we will supplement the field studies by using soil from both sites to explicitly examine the relationships between soil biodiversity and ecosystem functioning (respiration and nutrient mineralization).  This effort will contribute to the regionalization of the McMurdo LTER research on soil legacies and soil biodiversity.

In Taylor Valley and adjacent valleys, soil nematodes are the dominant invertebrate, occurring in more than 60% of more than 400 soils sampled to 10 cm depth, while rotifers and tardigrades occur in less than 3% of the soil samples. The distributions of Protozoa, Collembola and mites are still being elucidated. The species richness of soil invertebrate communities in Taylor Valley is very low compared with temperate habitats. Of these invertebrate groups, the nematodes are the most widely dispersed, and 3-4 nematode species occupy two levels in the soil foodweb, microbivore (bacteria/yeast) and omnivore/predator.

Since nematodes are at or near the top of the soil food web in Taylor Valley soils (and a more diverse group of invertebrates is expected at Cape Halett), we hypothesize that changes in their numbers and diversity is an indicator of changes in microbial communities.  However, a quantitative description of the relationships among organic matter, microbial communities (biomass and diversity) and higher levels in the food web, i.e. nematodes tardigrades and rotifers (abundance and diversity) is incomplete at both sites. Our current understanding of dry valley soil communities lacks explicit treatment of the links between microbial and invertebrate biodiversity. Since microbes dominate most terrestrial food webs (in biomass and energy flow), describing how microbial diversity responds to environmental gradients and climate variability is essential for understanding the assembly and functioning of more complex, i.e., invertebrate communities.

Measuring soil respiration with some extra helpers.

There are relatively few accounts of the diversity and/or abundance of microbial communities across gradients within either dry valley or coastal ecosystems, e.g. Cape Hallett. The cryptoendolithic communities of high elevation environments in the dry valleys have received the most attention. In dry valley soils, the number of microorganisms varies widely from ~ 0 to 107 g^-1 soil with the numbers and diversity of soil bacteria and yeast related to both climate and soil factors.

Microbial communities are expected to differ among typical dry valley soils and areas vegetated by moss and lichens and orthinogenic soils of coastal and maritime environments. In addition to the higher temperatures and greater soil moisture availability, soils at Cape Hallett are expected to have greater organic matter content, as well as a greater variety of composition due to the larger and more diverse distribution of vegetation. The quantity, quality and spatial variability of soil organic matter may be an essential factor limiting bacterial populations and diversity in soil communities of Victoria Land.  For example, Vishniac and Klinger (1988) found that yeast populations did not increase with soil wetting, but did so when a C substrate (glucose) was also added.

Portable DNA test kit ready to go.

We will employ a multifaceted molecular strategy, to identify, enumerate, and assess the metabolic activity of bacteria from soils in Taylor Valley and at Cape Hallett. Phylogenetic analyses (16 S rRNA) suggest that many Antarctic bacteria are new species or atypical strains of known species.  Wynn-Williams (1996) stresses that physiological and biogeochemical approaches must be integrated with molecular techniques to understand Antarctic microbial systems because it is the function of microbes in this extreme environment that is essential. Comparative analysis of the soil microbial community in conjunction with the proposed studies will provide a framework to determine how carbon, moisture content and changes in temperature mediate the structure and composition of the soil microbial communities.

Some of the abundant flora at Cape Hallett.