Storage and mineralization of carbon and nitrogen in soils of a frost-boil tundra ecosystem in Siberia

This study examines the carbon and nitrogen stocks of soils and vegetation in different frost-boil tundra microsites (rims, troughs and bare soil patches) and aims at elucidating differences in controls of organic matter turnover. Troughs, the wettest microsite, stored the greatest part of soil C and N (23.9 and 1.7 kg m−2, respectively), while drier rims held only 50% and bare soil patches only about 17% of the C and N found in troughs. Both C and N mineralization rates were higher in rims compared to troughs, suggesting a higher turnover of organic matter in rims. On an areal basis N was predominantly mineralized in mineral horizons, while C mineralization was more or less equally distributed between organic and mineral horizons. Thus, atmospheric warming, which has a stronger effect on the upper soil layers, may increase C mineralization to a higher extent than N mineralization (mainly located in lower soil layers). This suggests that frost-boil tundra ecosystems may be (at least in the short-term) sources of CO2 to the atmosphere. Furthermore, the combined results of gross N mineralization and net N mineralization measurements showed a higher microbial sink strength for N in rims compared to troughs, suggesting that decomposition of organic material in rims is controlled mainly by N availability, while the main factor constraining decomposition in troughs may be unfavourable hydrothermal conditions. This may lead to differential responses of frost-boil tundra microsites to changing climatic conditions.