Warming alters fungal communities and litter chemistry with implications for soil carbon stocks

Abstract

Rates of leaf litter decay are generally expected to accelerate with increasing temperature. However, chronic temperature elevation may cause changes in the quality of litter residues or in the composition of decomposer communities that result in unexpected decay responses. We performed a 23-month litter decomposition study at a long-term soil warming experiment to determine how soil warming affects litter decay rate, litter chemistry, extracellular enzyme activities, and fungal community composition. Experimental soil warming did not affect litter mass loss, but did result in a 23% increase in the relative abundance of lignin; a concomitant shift in enzyme activity wherein lignin-decomposing enzymes had higher activity in the heated treatment while cellulose-decomposing enzymes were suppressed; and a shift in the composition of the active fungal community. In particular, ectomycorrhizal fungi were three times more abundant in the heated treatment than the control, and shifts in fungal community composition were significantly correlated with the observed changes in extracellular enzyme activities. Our results suggest that warming altered the trajectory of decay resulting in litter residues enriched in lignin compounds and that were populated by a higher relative abundance of ectomycorrhizal fungi. These shifts may have altered the temperature sensitivity of litter decay by reducing the quality of litter residues and changing fungal community function.