Tree species mixture effect on extracellular enzyme kinetics varies with enzyme type and soil depth in subtropical plantations

Aims Tree species mixing is an essential measure used to increase soil carbon (C) sinks and enhance nutrient cycling, while enzyme catalysis is the rate-limiting step of soil C mineralization and nutrient release. The study aimed to determine how mixing affects soil C and nitrogen (N) hydrolases kinetics in subtropical plantations. Methods The topsoil (0–15 cm) and subsoil (45–60 cm) from two monoculture coniferous plantations and two mixed plantations formed by replanting broad-leaved trees in the two coniferous plantations were collected to analyze the maximum activity ( V max ), half-saturation constant ( K m ) and catalytic efficiency ( V max / K m ) of four hydrolases involved in C (β-glucosidase, BG; cellobioside, CB) and N (β-N-acetylglucosaminidase, NAG; leucine aminopeptidase, LAP) cycling. Results Mixing decreased the V max of BG but increased the V max of NAG in the topsoil, indicating the differential response of C and N enzyme activities to mixing. The K m of NAG and LAP increased, while the V max / K m of CB and NAG decreased after mixing in the topsoil. Mixing decreased the V max of CB and NAG and the V max / K m of BG and CB in the subsoil. The V max / K m values of C and N hydrolases were negatively correlated with SOC, total N and mineral N and positively correlated with the aromatic/aliphatic compound ratio, which illustrated that the hydrolases kinetics were mediated by changes in soil quality. Conclusion Mixing decreased the catalytic efficiency of soil C and N hydrolases in subtropical plantations, although the mixing effect on soil hydrolase kinetic parameters depended on the enzyme type and soil depth.