Microorganisms Control Litter Decomposition and Drive Grassland Soil C Stabilization by Regulating Exoenzymes

Litter decomposition and microbial activity are important factors affecting soil organic carbon (SOC) sequestration in the terrestrial ecosystems. However, how litter and microorganisms influence soil carbon (C) sequestration remains under debate, which hampers the understanding of C sequestration mechanisms. This study conducted a microcosm experiment by adding 13 C‐labeled litter from the grazed and fenced grasslands to clarify litter‐derived C dynamics and trace the C flow from litter to SOC pools. The results showed that the litter decomposition rate and litter‐derived C incorporated in dissolved organic C (DOC) in the fenced grasslands was lower than that in the grazed grasslands. Meanwhile, litter decomposition in the fenced grasslands formed a larger proportion of mineral‐associated organic C (MAOC, 8%) and microbial biomass C (MBC, 1%), compared with the grazed grasslands (3% and 0.3%). Hydrolase was positively correlated with the litter‐derived C in both particulate organic C (POC) and MAOC, whereas the oxidase: hydrolase ratio showed a negative correlation. Collectively, fenced grassland increased the percentage of litter‐derived C incorporation into both labile and stable SOC pools because of the higher exoenzymes than the grazed grasslands. These findings highlight the key roles of microbial exoenzymes in litter decomposition and demonstrate that microbial activity is conducive to SOC formation.