ObjectiveThe contents of soil carbon (C), nitrogen (N) and phosphorus (P) along with their stoichiometric ratios are varied due to the varying nutrient uptake and utilization strategies among plantations of various tree species, which in turn can affect soil microbial activity. However, whether soil microorganisms adapt to these changes by adjusting their biomass and extracellular enzyme stoichiometric ratios remains uncertain. This study aims to explore the effects of plantations of various tree species on soil-microbe-exoenzyme C∶N∶P stoichiometric ratios and to investigate the correlations among soil-microbe-exoenzyme stoichiometry.MethodsAn investigation into the contents of C, N and P, as well as microbial biomass C (C_mic), N (N_mic), and P (P_mic) was conducted, and the activities of C-(β-1, 4-glucosidase+β-D-cellosidase, BG+CBH), N-(β-1, 4-N-acetylglucosaminidase, NAG), and P-(acid phosphatase, ACP) acquiring extracellular enzymes for microorganisms at 0—40 cm depth in four native tree species plantations were determined. These plantations included conifers Pinus massoniana, deciduous broad-leaved Liquidambar formosana, Devergreen broad-leaved Schima superba and Elaeocarpus decipiens located in the hilly region of central Hunan Province and shared a common soil development and management history.Results1) Plantations of different tree species significantly affected soil C, N, P contents, microbial biomass, extracellular enzyme activity; C_mic∶N_mic∶P_mic and EEA_C∶N∶P. C_mic∶P_mic ratios in P. massoniana plantations and L. formosana plantations were significantly higher than those in S. superba plantations and E. decipiens plantations, indicating that microorganisms competed with plants for soil available P. The utilization rate of soil P was low, especially in L. formosana plantations. NAG and EEA_N∶P in S. superba plantations were the highest, suggesting that microorganism were obviously limited by N there. ACP in E. decipiens plantations was higher, EEA_C∶N and EEA_C∶P were also higher than those in plantations of other tree species, while EEA_N∶P was the lowest, indicating that microorganisms were most restricted by C and P there. 2) There was no significant correlation between soil C∶N∶P and microbial biomass, extracellular enzyme C∶N∶P, while only C_mic∶N_mic and EEA_C∶N, C_mic∶P_mic and EEA_C∶P showed significant negative correlation, indicating that there was no covariance between soil C∶N∶P and microbial biomass C∶N∶P. There was a significantly positive correlation between soil C_∶N_∶P and C_∶P_imb, a significantly negative correlation between C_mic∶N_mic∶P_mic and C∶N∶P_imb, and a significantly positive correlation between C∶N_imb and EEA_C∶N, which confirmed the influence of C, N and P differences between soil and microorganisms on the stoichiometric ratios of extracellular enzymes. 3) Existing biomass of the litter layer had significant effects on soil C, N, P contents, P_mic, C_mic∶P_mic, N_mic∶P_mic, BG+CBH, NAG, and EEA_C∶P.ConclusionBy influencing the contents of soil C, N and P, plantations composed of different tree species can affect microbial biomass and extracellular enzyme activities. Soil microorganisms can adapt to diverse nutrient limitations by regulating their biomass C∶N∶P ratios and synthesizing specific extracellular enzymes. The results substantiate the microbial resource allocation theory.