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At a high arctic, polar semi-desert site (79 degrees N) in Svalbard, nitrogen, phosphorus and potassium fertilizers were added to the soil for 5 yr to simulate increases in decomposition and nutrient mineralization which may occur as a result of increases in soil temperature and soil moisture caused by environmental change. Abundance of decomposer fungal species, isolated from standing-dead leaves of Dryas octopetala, varied between fertilized and unfertilized plots. Fungal biodiversity, as indicated by the Brillouin index, was lower in dead Dryas leaves from the fertilized plots, although more colonies were isolated from leaves of plants which had been fertilized. The fungi were cosmopolitan and not restricted to tundra areas. The dead leaves from the fertilized plots contained more nitrogen and phosphorus than those of the unfertilized plants. Leaves in the fertilized plots appeared to have been killed by winter injury resulting from an extended growing season in an atypically mild and wet autumn, which was followed quickly by extreme subzero temperatures.