Final Activity Report Summary - MYCCARFORSOIL (Mycelia of Ectomycorrhizal Fungi and Carbon Sequestration to Forest Soils) Plants are important for carbon (C) storage and reduce atmospheric CO2 pools, but soils contain much more C than aboveground parts. Ectomycorrhizal (EcM) fungi form symbiotic relationships with most tree roots and EcM mycelia (network of fungal hyphae), take up most nutrients needed for tree growth and receive a large portion of C (sugars) from photosynthesis, thereby acting as important pathways for soil C input. This project aimed at evaluating: - The amount of C input to forest soils via EcM mycelia. - The contribution of EcM fungi to total soil respiration (CO2-emission). - The role of nitrogen (N) deposition (from air pollution) on soil C input via EcM fungi, EcM species diversity and function. - Effects of elevated soil temperature on EcM fungi and soil microbes. All questions have been studied in mature forests in long-term controlled field experiments sites in Denmark, Sweden and Austria. C input to forest soils via EcM mycelia was mainly as fungal biomass, while no additional C seemed to be exported out of the fungal hyphae. EcM contributed to more than half of the fungal C, but could not explain the different patterns of C distribution in the soil profiles under six tree species at six sites. The relative contribution to soil respiration of tree roots and EcM hyphae was (in an intensively monitored mature beech forest) low in winter (below 10%) and increased in summer and early autumn (up to 35%). Total soil respiration increased 7.5 times from February to late August, while respiration from roots and EcM hyphae increased 16.5 times during the same period. It has not been possible to determine the contribution of EcM hyphae to soil respiration yet, due to slow colonization of the soil cores surrounded by fine nylon mesh that allow ingrowth of EcM hyphae, but not roots, although data indicate that it has started. N emissions from industry, transport and agriculture affects most ecosystems drastically. High N deposition at a forest edge, situated close to an N emission source, reduced the numbers of EcM roots and EcM mycelial production drastically (to only 16% and 1.5-2% respectively) compared to the interior of the forest with low N deposition (just 90 m away). N deposition changed the EcM species composition clearly. Functional shifts between the EcM communities along the gradient were investigated using 15N-labeled mixtures of an amino acid, ammonium and nitrate and EcM roots and hyphae took up more ammonium and least nitrate. In 30 spruce forests in Denmark and south Sweden total fungal biomass, EcM biomass in soil, and EcM mycelial production were all positively correlated with the C/N ratio of the forest floor, while only EcM mycelial production was correlated (negatively) with nitrate leaching, indicating an important role of EcM fungi in keeping N in the soil. Elevated soil temperatures stimulated EcM mycelial production in 100-year old mixed forests in Austria (70%) and in 40-year old spruce forests in north Sweden (50-135%), but no temperature adaptation among bacteria was found. The properties of forest soils were investigated using new efficient methods - analyses of Fluorescence (Fl) and Near Infrared (NIR) spectra. Influence of different tree species on soil properties were captured by FI, while NIR better separated samples from different sites. These two spectroscopic methods were nicely complementary and may give insights into soil chemical composition (NIR) and soil organic composition (Fl). Soil microbes and e.g. EcM hyphal N concentrations had some influence on NIR and Fl-spectra but need to be further evaluated. This project has taken several steps in transferring studies about EcM mycelia from the laboratory, out into the field and ecosystem studies, as intended. Achieved data from this project will be important in efforts to estimate and model effects of global climate change on forest soils and thus important for policymakers and for foresters.