The McMurdo Dry Valleys of Antarctica, a polar desert region, is an ecosystem at a threshold. Though extremely cold and dry, hydrologic linkages play an important role in determining soil stoichiometry, so altered liquid water availability resulting from climate variability can significantly influence nutrient distribution and biologic activity. To determine what elements are limiting to dry valley soil communities and how they will respond to alterations in soil stoichiometry, we are conducting field and laboratory experiments in which soil respiration and biomass are measured in response to carbon (C), nitrogen (N), phosphorus (P), CN, and CP additions. To determine the influence of geologic legacies on community response to nutrient additions, we used soils from two sites: Fryxell Basin, where N<P, and Bonney Basin, where N>P. To investigate the mechanisms involved in community response, a microcosm vessel containing 10 g of soil from long-term nutrient fertilization plots were incubated for three weeks. 13C and 15N were added, and the fate of those stable isotopes was measured in the soil and headspace to identify whether denitrification or stimulation of in situ C utilization is occurring. Additionally, a CNP treatment was included to determine the synergistic influence of all three nutrients.
In this microcosm of soils from both sites, we observed a significant increase in soil respiration under the addition of CN, such that respiration under CN treatments were 2-3 times higher than all other treatments, which were statistically similar. This CN stimulation gradually decreased over two weeks following treatment application, with a smaller but longer pulse in Bonney Basin soils. To observe a CN-induced pulse at both basins was surprising, as we expected a CN pulse at only one site (Fryxell, where N<P) and a CP pulse at the other (Bonney, where N>P). We found little evidence for P-limitation at either site, as the CNP treatment did not differ significantly from CN. The only deviation was a larger pulse under CNP in Bonney soils on only the first sampling date; at all other points the CNP treatment responded the same as the CN treatment. Isotope data are currently being processed to illustrate the fate of the nutrient treatments and identify potential mechanisms by which soil communities respond to an increase in available nutrients. Preliminary results demonstrate that predicted future climate warming can significantly alter biological activity and soil biogeochemistry through changes in the relative availability of C and N.