"The Arctic is currently facing large changes in climatic conditions, with expected consequences for the vulnerable terrestrial ecosystems. Arctic ecosystems contain a large proportion of the global soil carbon stock, and there is a risk that environmental changes will lead to a release of carbon dioxide from this pool substantially amplifying the atmospheric warming potential. However, populations of plants and microorganisms will likely change with changed environmental conditions. An increased abundance of plants associating with ectomycorrhizal (EM) fungi has already been observed across the arctic tundra biome as a response to recent warming, and this trend is expected to continue. Recent research suggests that EM mycelia contribute disproportionately relative to plant inputs to soil organic matter formation. Hence, increased abundance of EM plants and fungi could partly counterbalance the expected respiratory loss of carbon from tundra soils in the future. However, EM fungi also contribute to the degradation of organic matter by producing extracellular enzymes thereby decreasing carbon storage. It is crucial to sort out which of these mechanisms dominate in different ecosystems and under different environmental conditions in order to build reliable conceptual and predictive models describing the future carbon balance of the Arctic. This project is the first to explore the role of EM fungi as drivers of soil carbon dynamics in the Arctic in relation to global change. The project explores responses of EM fungi at three interlinked levels, that is, their abundance, species composition and functioning, to long-term field experiments simulating climate change in the sub- and high arctic. The project combines methods to measure ecological pools and processes (soil C and N pools, 13C and 15N natural abundance) with novel methods for studying EM community composition and functioning (fungal ingrowth bags, molecular community analyses, exoenzyme production)."