The role of mycorrhizal colonization in coupling C and N cycles in diverse tree stands

Most temperate tree species are predominantly associated with either arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi, which provide mineral nutrients to their host in exchange for carbon (C). As the two mycorrhizal types differ fundamentally in their nutrient economy, they were suggested to provide an integrated index of biogeochemical transformations relevant to C cycling and nutrient retention in forests. Yet little is known about the group-specific role of mycorrhizal type in the relationship between tree diversity and ecosystem functions. The main objective of my Heisenberg research project was to determine the differences between functional groups in rhizosphere C fluxes between diverse AM and ECM tree stands. Among the key biogeochemical processes, I focus on root exudation and decomposition, which represent the cause and consequence of the microbial priming effect to stimulate nutrient release from soil organic matter. Based on the assumed organic nutrient economy of ECM stands, I hypothesize that enhanced root exudation is a primary mechanism by which ECM trees maintain productivity in diverse forest stands, while diverse AM stands mainly depend on nutrient transfer via leaf litter. In my talk, I will derive the importance of mycorrhizal association type as a functional grouping for understanding biogeochemical cycling under climate change, present some results on the mycorrhizal control of biodiversity effects in forests, and discuss open knowledge gaps.