FUNGI AS DRIVERS OF ECOSYSTEM RESPONSE TO GLOBAL CHANGE
Microbes are the engines of carbon (C) cycling in soils, which hold 2-3 times more C than the atmosphere. Fungi represent a significant component of the microbial community in many ecosystems, and in particular, are the primary agents of decomposition in temperate forests. Fungal-mediated decomposition is known to be sensitive to stressors such as atmospheric nitrogen (N) deposition and rising global temperatures, but we lack a mechanistic understanding of the traits that determine responses to environmental change. Here I use a combination of soil biochemical assays, environmental metabarcoding, lab-based culture techniques, and whole-genome sequencing to describe the responses of whole fungal communities and underlying physiological attributes to simulated N deposition and increased temperature. I show that a shift from lignin-decomposing saprotrophs to yeast species with low relative activity levels can partly explain reduced decomposition rates in N-fertilized forests. Similarly, experimental soil warming favors ectomycorrhizal fungi over saprotrophs causing reduced decay rates relative to thermodynamic assumptions. Finally, I show that the efficiency with which fungi convert C resources into biomass is generally decreased by temperature and is linked to life-history traits such as dispersal strategy and growth rate. Together my results provide an understanding of both how and why fungal communities respond to a changing climate.