Structural equation model (SEM) analysis of N and P addition-induced causal relationships among Nitrate, Soil pH, available P, number of nodules, Microbial biomass carbon, Root biomass, and soil respiration (Soil R) under P addition and N addition treatments in pot soybean (χ² = 15.203, df = 23, P = 0.887, CFI = 1, RMSEA < 0.001). Within the models, the positive and negative values on the arrows indicate positive and negative relationships between the variables, respectively. Solid and dashed arrows suggest significant and non-significant paths, respectively. R² values represent the proportion of variance explained for each variable.  *P < 0.05, **P < 0.01, ***P < 0.001.