Exploring the soil food web structure and carbon dynamics of the McMurdo Dry Valleys LTER, Antarctica

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In the McMurdo Dry Valleys, Antarctica there are two basic soil food webs: wet (lake and stream margins, <5% of the valley) and dry (~95% of the valley). The “wet” food webs thrive in moss or algal mats and have relatively high faunal diversity, which includes nematodes (genera include: Eudorylaimus, Plectus, and sometimes Geomonhystera and Scottnema) tardigrades, rotifers, and occasionally collembolans and mites. The “dry” food web has low faunal diversity (often just one nematode species, Scottnema lindsayae). Some species occasionally occur in both food webs, and community composition varies depending on habitat suitability. The carbon sources that support the energetics of dry valley soil food webs are poorly understood. We ask the following questions: How is food web complexity and structure related to the varying carbon sources throughout the dry valleys? How does the dry valley soil food web structure vary with habitat, climate, and time? We hypothesize that: 1) The dry food webs derive most of their energy from legacy-C (marine, lacustrine or ornithological sources) while the wet food webs mainly use contemporary-C (recently photosynthesized), and 2) The amounts of these C sources to support trophic structure depends on soil moisture and temperature. The focus of this poster will be to present plans for a field study and laboratory experiment to test these hypotheses, along with preliminary field results. We sampled soil from sites throughout Taylor Valley that have been identified as having distinct legacy-C sources (marine, lacustrine or ornithological) or the presence of contemporary-C (algal mats). We collected soil and fauna from these diverse habitats and identified the trophic position of nematodes, tardigrades, and rotifers using variations in the natural abundance of stable isotopes (13C and 15N). Our ensuing laboratory study seeks to further explore how soil carbon dynamics are affected by food web complexity and increasing soil moisture. By adding 13C-labeled algae to soil with legacy-C we are tracing the two C sources (legacy vs. contemporary) through the soil food web as a function of soil moisture. We are looking to form predictions about the level of soil moisture that would cause a tipping point in food web structure from “dry” to “wet”, moving the soil food web into a new functional state.