Development of ectomycorrhizas in model beech–spruce ecosystems on siliceous and calcareous soil: a 4-year experiment with atmospheric CO2 enrichment and nitrogen fertilization

To study responses of forests to global change, model ecosystems consisting of beech and spruce trees were established in open top chambers. The ecosystems were exposed to four conditions for 4 years, each replicated four times: ambient and elevated CO2, and low and high nitrogen input. At the end of the trial, the trees were 6–8 years old. Each chamber contained two separate compartments with siliceous and calcareous soil. Here, we focus on the development of ectomycorrhizas in the topsoil layer. Ectomycorrhizal fungal biomass associated with the fine roots, estimated by using ergosterol content as a marker, was much higher in the siliceous compared to the richer calcareous soil. Also, in root-free soil samples, the level of ergosterol, indicative of the extraradical mycelium of ectomycorrhizal fungi as well as the mycelium of other fungi, was about six times higher in the siliceous than in the calcareous soil. Conditions of elevated atmospheric CO2 primarily affected ectomycorrhizas in the calcareous soil. Fungal biomass, calculated per soil volume of the top soil layer, increased significantly, as did the metabolic activity of the ectomycorrhizal fungi, measured as uptake of glucose and synthesis of trehalose. Conditions of nitrogen fertilization affected ectomycorrhizas in the siliceous, nutrient poor soil.