My study is focussed on the effects of global changes on subarctic microbial communities in the soil. From previous studies in Cassiope-dominated heaths in the area it is known that experimental warming simulating expected effects of climatic change in this century might affect microbial communities and their activity, for instance shown by changes in trophic structure of nematodes and exchange of greenhouse gases. However, microbial reponses to warming and enhanced nutrient turnover as a result of greater litter supply in more species- and nutrient-rich heaths are not known. The current study will be a part of a long-term global change research project in which 24 plots in a species-rich heath near the heliport in Abisko have been manipulated since June 1999. The aim of my M.Sc. project is to reveal some of the responses of the soil microbial communities to three years of warming and enhanced litter supply. A suite of parameters within the field of microbial biomass, activity and diversity will be measured throughout the plant growing season, or in a final harvest at the end of the season.