FAB1: Soil microbial community structure predicts fungal necromass decomposition rates across diverse temperate forest types

Although dead fungal mycelium (necromass) represents a key component of biogeochemical cycling in all terrestrial ecosystems, how different ecological factors interact to control necromass decomposition rates remains poorly understood. In this study, we assessed how edaphic parameters, belowground plant traits, and soil microbial community structure predicted the mass loss rates of different fungal necromasses within experimental monocultures of 12 tree species in Minnesota, USA. Necromass decay rates were most strongly driven by initial chemical composition, being significantly slower for fungal necromass with higher initial melanin content. Of the extrinsic ecological factors measured, variation in the amount of mass remaining of both low and high melanin necromass types was significantly directly predicted by soil microbial community composition, not by soil microclimatic or plant trait parameters. Further, the microbial communities governing decay rates varied depending on the initial necromass chemical composition, suggesting that the extrinsic and intrinsic factors interact to drive decomposition. Collectively, these results suggest that, after the chemical composition of the dead fungal residues, soil microbial communities represent the main drivers of soil necromass degradation, with potentially large consequences for soil carbon sequestration and nutrient availability.