Field and Microcosm Studies of Decomposition and Soil Biota in a Cold Desert Soil

Abstract

In the extreme cold desert soil of the McMurdo Dry Valleys of Antarctica, we studied the effects of changing moisture and temperature on rates of decomposition and the activity and abundance of soil organisms. Our objective was to understand how moisture and temperature structure invertebrate communities and control important ecosystem processes and soil biotic activity in this extreme environment. First, in a field experiment, we manipulated soil moisture and temperature and compared cotton strip decomposition rates at two dry valley sites with different moisture regimes. At both sites, live nematode abundance and activity were unchanged by soil treatments over the 2-year study. In the same plots, the cotton strips did not decompose, despite soil warming and the addition of moisture. The results suggest that biological activity in the McMurdo Dry Valleys is severely limited and that soil organisms are not responsive to improving environmental conditions. Second, in microcosms, we manipulated dry valley soil moisture at a constant temperature of 10°C and measured the rates of key soil processes. Soil respiration, nitrification, and the decomposition of cotton strips were all greater in dry valley soils that were wetted to 10% moisture content, as compared to soils at 0.6%. These results indicate that the decomposition potential for dry valley soils is high when moisture and temperature limitations are removed. In the field, however, this process was extremely slow, and biota did not respond to improving environmental conditions. Soil processes appear to be limited primarily by the extreme desiccation of the dry valleys. Ecosystems processes are likely restricted to the brief periods following infrequent snowfall, melt, and soil wetting that permit the activity of soil microbes and biota.