Simulated climate change affecting microorganisms, nematode density and biodiversity in subarctic soils

Arctic terrestrial ecosystems are strongly dominated by temperature, and gl obal warming is expected to have a particularly strong impact in high latit udes. The Arctic will therefore be an important region for early detection of global change. In the present study the effects of environmental manipul ations simulating climate change on soil microorganisms and nematode popula tions were investigated. Study sites were a dwarf shrub dominated tree-line heath (450 m a.s.l.) and a high altitude fellfield (1150 m a.s.l.) at Abis ko, Swedish Lapland. Soil temperature was enhanced by using passive greenho uses and the impact on soil organisms with and without NPK fertilizer addit ion was assessed. The nematode community was strongly affected by warming a nd nutrient application. Population density was twice as high for all treat ments at the fellfield as compared to controls. At the heath temperature en hancement with or without fertilizer application also led to a doubling of the population density, whereas fertilization alone caused an increase of a bout one third. The environmental manipulations resulted in a greater micro bial biomass C and active fungal biomass in the heath soil. Increased densi ty was also recorded for bacterial and fungal feeding nematodes at both sit es. The results suggest that nematodes have an important impact on microbia l biomass and turnover rates in the two subarctic systems. Elevated soil te mperature apparently will lead to increased grazing on microorganisms, cont ributing to enhanced net N and P mineralization rates and plant nutrient av ailability. However, biodiversity was generally affected negatively by the environmental manipulations. The effects were more severe at the high altit ude fellfield indicating that the influence of elevated temperature will be more pronounced in systems already stressed by extreme climatic conditions .