Mycorrhizal fungi modulate tree diversity effects on nutrient dynamics

Species-specific differences in nutrient acquisition strategies allow for complementary use of resources among plants in mixtures, which may be further shaped by mycorrhizal associations. However, empirical evidence of these relationships is scarce, particularly for tree communities. We investigated the impact of tree species richness and mycorrhizal types, arbuscular mycorrhizal fungi (AM) and ectomycorrhizal fungi (EM), on the above- and belowground carbon (C), nitrogen (N), and phosphorus (P) dynamics. Soil and microbial biomass elemental pools did not strongly respond to tree species richness or mycorrhizal type. Tree species richness increased foliage C and P pools depending on mycorrhizal type. Additive partitioning analyses showed that net biodiversity effects for C, N, P pools in EM tree communities, and N pools in AM tree communities, were driven by selection effects, while mixtures of both mycorrhizal types were influenced by complementarity effects. Furthermore, tree species richness enhanced soil nitrate uptake over two years but had no impact on ammonium and phosphate levels. Our results indicate that positive effects of tree diversity on aboveground nutrient storage are mediated by complementary mycorrhizal strategies. Given the prevalence of anthropogenic impacts on tree species richness globally, these results may have important implications for reforestation of multifunctional forests.