Fig. 8

Predicted partial least squares path modeling (PLS-PM) showing the effects of biotic and abiotic factors on the changes in SOC content (a) and nutrient availability (b). In the structural model, the lines indicated paths, and the values adjacent to the lines denote the magnitude of the path coefficients calculated by PLS regression. R² values are shown for all endogenous latent variables. Values in the measurement model represent the loadings between a latent variable and its indicators. The figure shows the final models after the model diagnosis processes. Specifically, some of the changes in the regulating factors were removed because of low loading (|loading|< 0.70). The * denote significant pathways (p < 0.05). The Pseudo Goodness-of-Fit (GoF) of model (a) and model (b) is 0.42 and 0.17, respectively. MAT, mean annual air temperature; MAP, mean annual precipitation; C_org, soil organic carbon; N_t, total nitrogen; P_t, total phosphorus; C:N, the ratio of soil organic carbon to total nitrogen; NH₄⁺, ammonium; NO₃⁻, nitrate; available phosphorus, available P; Hy-EEAs, hydrolases-extracellular enzymes activities; Ox-EEAs, oxidoreductases-extracellular enzymes activities; C_mic, microbial biomass carbon; N_mic, microbial biomass nitrogen; P_mic microbial biomass phosphorus