Divergent responses of carbon-degrading enzyme activities to litter alterations: Implications for soil respiration

Climate change affects the amount of plant litter inputs to soils around the world, with cascading effects on soil respiration (SR). Soil extracellular enzymes catalyze the rate-limiting steps in soil organic matter decomposition, and can be considered as proxies for SR. Soil cellulase and ligninase are two dominant carbon (C)-degrading enzymes, targeting the decomposition of readily decomposable and structurally complex C pools, respectively. However, whether and how changes in aboveground plant litter inputs influence soil cellulase and ligninase activities as well as the implications for SR remains poorly understood. We conducted a global meta-analysis on the responses of soil cellulase and ligninase activities and SR to litter addition or removal by synthesizing data from 55 studies with the aim of linking soil enzyme activity to SR. Litter addition significantly increased cellulase activity by 25.2%, whereas litter removal significantly decreased it by 25.9%. In contrast, neither litter addition nor removal influenced ligninase activity. The changes in cellulase activity correlated positively with changes in SR, but no such relationship was found for ligninase activity. In addition, the effects of litter addition and removal on cellulase activity decreased with treatment duration. These results indicate that litter alterations affect SR primarily by controlling the microbial decomposition of readily decomposable rather than structurally complex C pools. Altogether, we suggest that the total and long-term effects of litter alterations on SR might be smaller than previously thought.