Fig. 7
Contribution paths of bacterial α-diversity, Azotobacter, and nitrogen cycle genes to nitrogen contents in soil and plants. Piecewise SEM showed that bacterial α-diversity, Azotobacter, and nitrogen cycle genes had direct and indirect effects on alkali-hydrolyzed nitrogen content in soil (A); they had direct effects on total nitrogen content in soil (B). Each composite variable contained several measurement variables. Numbers adjacent to the arrows are path coefficients; the arrow thickness indicates the strength of the relationship. The proportion of variance explained (i.e., R2) appears below each composite variable in the model at the following significance levels: *P < 0.05, **P < 0.01, and ***P < 0.001