Fig. 4

Partial least squares structural equation modeling (PLS-SEM) analysis of the relationships between treatment, soil properties, and leaf C, N, and P content and their stoichiometry of (a,c) Camellia sinensis var. assamica and (b,d) Camellia sinensis var. sinensis. Standardized path coefficients representing the effect sizes of potential causal variables are indicated by numbers adjacent to arrows. The width of arrows is proportional to the potential causal effect between variables. The red arrows indicate positive effects, and the blue arrows indicate negative effects. The numbers in the ellipse of response variables denote the explained variance (R²). Colors of rectangles and ellipses indicate different variable types. The variables in the rectangles represent observed variables, while the variables in the ellipses represent latent variables. The observed variables of ‘Treatment’ are unfertilized and fertilized. The observed variables of ‘Soil nutrient elements’ are the contents of soil total N, NO₃⁻-N, NH₄⁺-N, total P, and available P. The observed variables of ‘Soil C: N:P stoichiometry’ are soil C: N, C: P, and N: P. The observed variables of ‘Leaf macroelement’ are leaf C, N, and P contents. The observed variables of ‘Leaf C: N:P stoichiometry’ are leaf C: N, C: P, and N: P. CSA, Camellia sinensis var. assamica; CSS, Camellia sinensis var. sinensis. SOC, soil organic carbon; SMC, soil moisture content. The goodness-of-fit was used to assess the model. Significance levels: ***, P < 0.001; **, P < 0.01; *, P < 0.05.