Divergent responses of soil enzyme kinetics to altered precipitation across steppes with varying historical precipitation

Soil extracellular enzymatic catalysis is the rate-limiting step in soil organic matter decomposition, and V_max and K_m are enzyme kinetic parameters reflecting enzyme catalytic capacity. However, it is still far from clear how these enzyme kinetic parameters respond to altered precipitation and subsequently influence soil microbial respiration (R_h). Here, we examined the V_max and K_m of seven soil hydrolytic enzymes and polyphenol oxidase (PPO), R_h, and microbial biomass carbon (MBC) under altered precipitation (− 30%, ambient, and + 30%) across Desert, Typical, and Meadow steppes. The results showed that the V_max of hydrolytic enzymes and PPO were higher in the meadow than desert and typical steppes. Drought decreased the V_max of C-, N-, P-degrading enzymes and PPO in the desert and typical steppes, but these changes were not observed in the meadow steppe, indicating the greater sensitivity of V_max to altered precipitation in drier ecosystems. Similarly, there were the same patterns of R_h and MBC induced by changes in precipitation. However, changes in precipitation differently affected K_m depending on enzymes and ecosystem types. Changes in V_max of enzymes positively correlated with changes in soil moisture and belowground net primary production. Moreover, the V_max and K_m of β-glucosidase (BG) and the V_max of leucine aminopeptidase were the best predictors for variability in R_h. Partial least squares path modeling further revealed that R_h response to altered precipitation was directly regulated by kinetic parameters of BG and V_max of leucine aminopeptidase, rather than by MBC. These findings provide important insights into the linkages between soil hydrolase kinetics and R_h, advancing our understanding of the mechanisms of soil organic matter decomposition under climatic change.