In the research project ForHot we study the effects of increased soil temperature on forest and grassland ecosystems. The setup of this project is unique, due to soil warming as the results of a shift in geothermal area after the earthquakes in 2008. Belowground channels of naturally hot water at different soil depths create soil temperature gradients, ranging from +0°C to >+35°C, which is an optimal condition to study ecosystem responses to the warming. In this talk we will present preliminary results on the effects of increased soil temperature on litter decomposition and ectomycorrhizal abundance and diversity in a 45 year old Sitka spruce (Picea sitchensis) forest.

Results on the effects of increased soil temperature on ectomycorrhizae were obtained by studying ectomycorrhizal root tips on spruce roots from natural soil samples and the growth of fungal mycelium into mesh bags in the forest topsoil. The amount and diversity of fungal mycelia in bags was assessed and the mycorrhizal root-tips were counted and classified, based on morphological characteristics.

A litter decomposition of Sitka spruce needle litter was assessed by placing mesh bags with the needle litter on top of the soil and harvesting them with regular interval over a one year period. The changes in needle litter mass were calculated and the decomposition rates at different temperatures were compared.