Two typical soil foodwebs exist in the McMurdo Dry Valleys, Antarctica. These are: wet and dry. The “wet” soil foodwebs are associated with moss and algae mats in stream or lake margins (<5% of area) and have relatively high faunal diversity, which can include several genera of nematodes, tardigrades, rotifers, and microarthropods. The “dry” foodweb (~95% of area) has low faunal diversity (often just one nematode species, Scottnema lindsayae). Various combinations of fauna communities exist depending on habitat, resources, and location, but questions remain about organic carbon (C) sources that fuel these foodwebs’ energetics. Soil organic C is extremely low. While it includes minor contemporary-C of algal, moss, or cyanobacterial sources, the majority of soil organic C is legacy-C derived from late Pleistocene era lake algal deposits. We asked: How are foodwebs related to C source, habitat, and elevation? We hypothesized: 1) “dry” foodwebs at low elevation use lacustrine legacy-C while “dry” foodwebs at high elevation (above historic lake levels) use wind-deposited marine, ornithological, or contemporary-C sources; 2) “wet” foodwebs use contemporary-C at all elevations. In a field study, we sampled wet and dry soil at both high and low elevations at three sites from valley mouth to end. We identified distinct legacy-C sources (lacustrine, marine, ornithological) and contemporary-C sources (algae, moss) based on unique 13C and 15N signatures. Next, we identified trophic position of nematodes, tardigrades, and rotifers using natural abundances of 13C and 15N.
Results showed: 1) C sources identifiable with unique isotopic signatures, 2) three distinct trophic levels, 3) different isotope signatures for C source and fauna in wet vs. dry habitats and high vs. low elevations, and 3) differing foodweb structure among C sources. Wet soil C and fauna were associated with algal sources, while low elevation dry soil C and fauna were linked to lacustrine legacy C sources. The high elevation dry soil foodwebs had isotopic signatures outside the range of lacustrine legacy-C, and used either marine or contemporary-C sources. Several fauna groups were only or predominantly found associated with contemporary-C, while S. lindsayae was primarily in dry areas of legacy-C. This research reveals that Antarctic Dry Valley soil foodwebs take advantage of multiple C sources across the landscape, knowledge key to understanding how these ecosystems function.