Fig. 3: Path diagram for Piecewise structural equation modelling showing only significant direct and indirect effects of soil abiotic variables and N-cycle microbial communities on tree health status.

Numbers adjacent to the arrows are standardised path coefficients, analogous to relative regression weights and indicative of the effect size of the relationship. Solid and dashed arrows indicate positive and negative relationships, respectively. Double-headed arrows indicate covariance between variables, single-headed arrows indicate a one way directed relationship. Blue arrows indicate the relationship between soil variables, red arrows indicate the relationships between soil variables and gene abundances, grey arrows indicate the relationships between gene abundances and green arrows indicate the relationship between gene abundances and tree health status. The width of the arrow is proportional to the strength of path coefficients. The proportion of variance explained (conditional R²) appears below every response variable in the model. Significance levels are as follows: *P < 0.05, **P < 0.01 and ***P < 0.001.