Carbon and nitrogen dynamics affected by litter and nitrogen addition in a grassland soil: Role of fungi

Abstract

Fungi are critical for carbon (C) and nitrogen (N) dynamics in forest soils, but much less is known about their activity in grassland soils. Here we examined how fungal activity affected C and N cycling in a grassland soil with and without litter and N addition. Soil from a semi-natural grassland was amended with and without a fungicide (cycloheximide) to manipulate fungal activity, with and without N (20 mg N kg−1 soil as KNO3), and with and without grass litter (27 g litter kg−1 soil). Soil respiration, N2O emission, gross N mineralization, microbial biomass C (MBC) and N (MBN), available NH4+, NO3−, dissolved organic C (DOC) and N (DON) were measured during a 10-day incubation experiment. We observed that the fungicide decreased soil respiration on average by 59% but increased gross N mineralization on average by 59% with litter addition. Fungicide addition decreased N2O emission both with and without litter addition. Furthermore, N addition enhanced fungal activity, but only with litter addition when fungi became limited by N. We conclude that fungi play an important role in decomposing litter and N2O emission in grasslands but that fungal activity is sensitive to external N addition without litter inputs.