Distribution and dynamics of soil organic matter in an Antarctic dry valley

Terrestrial ecosystems in the Antarctic dry valleys function under extremely cold and dry climatic conditions that severely constrain C and N cycling and, like other polar regions, are likely to be sensitive to environmental change. To characterize the distribution and dynamics of soil organic C (SOC) and N in the various landscape elements of an Antarctic dry valley, we measured soil profile organic C and organic N stocks, inorganic N (NH4–N and NO3–N), soil CO2 effluxes, water contents and soil temperatures in the Garwood Valley, a relatively small valley in southern Victoria Land. We also conducted laboratory measurements of basal respiration on soils collected from the Valley. SOC and respiration rates were low and SOC was highly stratified in the soil profile, with the largest values observed near the surface. Significant variations of SOC stocks and soil CO2 effluxes were observed between landscape elements and spatial variability was closely related to the distance from the lake, the major site of primary production. The fastest rate of SOC turnover (residence time c. 30 years) was found in the soils at the lake edge, slower rates were found in landscape elements close to the lake (c. 52–67 years), and the slowest rates in other landscape elements (c. 84–123 years) further away. A mass balance of organic C indicates that the quantity of C fixed in the lake, accumulated on the lake edge, exposed and subsequently displaced on a 14-year basis can explain the near-surface SOC turnover within the entire valley. We conclude that the displacement of organic matter derived from the lake is an important external source for the microbial processes in these soils at a landscape scale. However, further investigations are needed in order to evaluate the importance of displaced C compared to other nutrients (e.g. N) on the spatial control of observed soil respiration rates.