Linking soil extracellular enzymes with soil respiration under altered litter inputs

Climate and land-use changes have altered both litter quality and quantity, with cascading impacts on soil respiration (SR). Soil extracellular enzymes (EEs) like cellulase and ligninase are crucial for deconstructing plant litter because they convert polymers into monomers. However, whether and how changes in litter inputs influence soil cellulase and ligninase activities as well as the implications for SR remain poorly understood. We conducted a global meta-analysis of 827 observations on the responses of SR and soil cellulase and ligninase activities to litter addition and litter removal. Litter addition significantly increased cellulase activity by 25 %, whereas litter removal decreased it by 26 %. Neither litter addition nor litter removal affected ligninase activity. Changes in cellulase activity correlated positively with SR under both litter addition and litter removal, but no such relationship was found for ligninase activity. These results indicate that changes in litter inputs affect SR primarily by affecting the microbial decomposition of readily decomposable rather than more structurally complex carbon pools. In addition, the effects of changes in litter inputs on cellulase activity decreased with treatment duration, suggesting that the long-term effects of changes in litter inputs on SR might be smaller than previously thought. Our results underscore the dominant role of cellulase in mediating the responses of SR to altered litter inputs. Integrating cellulase responses to altered litter inputs into Earth system models could improve the representation of microbial processes and refine the predictions of soil carbon dynamics.