Responses of Soil C-, N-, and P-Hydrolyzing Enzyme Activities to N and P Addition in an Evergreen Broad-Leaved Forest in Southwest China

Background and Aims Human activities-mediated input of nitrogen (N) and phosphorus (P) to ecosystem may significantly affect soil hydrolyzing enzyme activities (Hy-EAs). However, the mechanisms underlying the responses of soil Hy-EAs to change in N and P availability remains unclear. Methods Here, a two-year field N and P addition experiment was conducted in a subtropical evergreen broad-leaved forest to elucidate the effects of N addition, P addition, and NP co-additions on soil Hy-EAs and biochemistry properties. Results The invertase, cellulase, and acid phosphatase activities were increased in N treatment but reduced in P treatment. The urease activity was reduced in N treatment but did not alter in P treatment. NP treatment significantly increased the invertase and cellulase activities. Furthermore, the cellulase activity was positively correlated with soil organic carbon concentration. The acid phosphatase activity was negatively correlated with microbial biomass carbon (MBC), total P, and available P concentrations. Whereas the urease activity was not strongly dependent on total N concentrations, but positively correlated with soil pH and MBC. These Hy-EAs were significantly correlated with C-to-P and N-to-P ratios, while no significantly correlation with C-to-N ratio. Conclusions Overall, our results indicated that N and P addition significantly affected the soil C-, N-, and P-hydrolyzing enzyme activities. With ongoing imbalanced N and P input in our studied subtropical evergreen broad-leaved forest, N addition may exacerbate the limitation of soil C and P availability, while the exogenous P addition may improve the soil C and P availability.