Regional-scale biogeographical patterns of soil extracellular enzyme activities across eight Chinese fir plantation locations

Chinese fir (Cunninghamia lanceolata) is the most important conifer tree species in plantations in subtropical China. Soil extracellular enzyme activities (EEAs) play key roles in mediating multiple forest ecosystem functions, such as organic matter decomposition, nutrient cycling, and plant productivity. In this study, the activities of five soil extracellular enzymes and their stoichiometric (EES) features were investigated at eight Chinese fir plantation locations. The results showed that the soil EEAs exhibited distinct biogeographic differences and were primarily affected by the spatial heterogeneity of soil nutrients. We found that the soil EES was strongly influenced by soil pH and mean annual temperature. Moreover, soil properties were found to be more important than climatic factors in influencing changes in soil microbial nutrient restrictions based on vector length (0.43 vs. −0.1). Random forest analysis indicated that changes in microbial nitrogen (N) and phosphorus (P) limitations were mainly affected by soil NO₃⁻-N and dissolved organic carbon (DOC), whereas soil microbial C limitation was largely influenced by pH, DOC, and total C content. This study sheds light on how soil and climatic factors affect soil EES in subtropical Chinese fir plantation ecosystems and provides useful insights for the development of management strategies to improve the productivity of Chinese fir forests.