Abstract
Continuous high levels of nitrogen (N) deposition and more intensive harvesting of forest residues will drive many forests in southern Sweden from nitrogen to phosphorus limitation. This may lead to leakage of N to the groundwater, eutrophication of streams and lakes and progressively lower forest productivity due to depletion of soil nutrient stocks. Ectomycorrhizal fungi (EMF) respond strongly to N and phosphorus (P) availability and these fungi have a fundamental role in N and P uptake, as well as in C accumulation in forest soil. We demonstrated recently that up to 70% of the humus layer in late successional forests in northern Sweden originate from roots and root associated fungi. Studies will be performed in chronosequences, elevational gradients, experimental sites and laboratory systems undergoing transitions from N to P limitation. We will combine measurements of EMF growth and activity using mesh bags and isotopically enriched soil organic matter (SOM) with state-of-the-art techniques (FTIR, NEXAFS, STXM) to analyze the chemical changes of SOM that take place when is colonized by EMF. The capacity of EMF to take up P from poorly soluble sources (P adsorbed on oxides) will also be studied along the same gradients The main objective is to enhance our understanding of the role of EMF for carbon sequestration, N retention and P uptake in forest ecosystems undergoing a transition from N to P limitation.
Sweden