Responses of Soil Extracellular Enzymes to N and P Additions Vary Between Temperate and Subtropical Forests

Microbial extracellular enzyme activities (EEAs) and their stoichiometric characteristics are valuable proxies for understanding soil organic matter (SOM) decomposition. Soil microbes are generally rich in nitrogen (N) and deficient in phosphorus (P) in subtropical forests, whereas the opposite pattern is often observed in temperate forests. Despite increasing N deposition and P addition, the response of EEAs to these differences between temperate and subtropical forests remains largely unexplored. We measured microbial carbon (C)-, N-, and P-acquiring EEAs in a temperate and a subtropical forest under N and/or P additions. We analyzed microbial resource allocation and nutrient limitations using extracellular enzymatic stoichiometry ratios and vector analysis. The results showed that N additions had weak effects on microbial EEAs, resource allocation, and nutrient limitations in both forests. In contrast, P additions enhanced C- and N-acquiring enzymes in both forests, promoting P-acquiring enzyme and oxidases in the temperate forest while suppressing them in the subtropical forest. Our results suggested that EEAs were more responsive to P than to N addition in both forests. Additionally, the convergence of extracellular enzymatic stoichiometry ratios toward 1 with P additions in both forests indicated a more balanced allocation among C, N, and P. Vector analysis revealed that soil microbes in both forests were P-limited. Furthermore, soil available P strongly correlated with microbial EEAs and their stoichiometric characteristics. Overall, our findings highlight the crucial role of P availability in influencing microbial responses to N deposition and P addition in temperate and subtropical forests.