Figure 4. The direct and indirect effects of temperature and nutrients on biodiversity.

The effects of temperature (Tem), nutrient enrichment (Nut) and primary productivity (Pro) on bacterial diversity (Div) and community composition (Com) for Norway (a,c) and China (b,d), explored with partial least squares path model. For diversity (a,b) and community composition (c,d), species richness and the first axis of nMDS were used as observed variables. For temperature, water temperature and its squared value were used. For nutrient enrichment, the observed variables included the initial levels of added NO₃⁻ and measured NO₃⁻, NO₂⁻ and PO₄³⁺. For primary productivity, the observed variables were pH and Chl a. Shown are the path coefficients calculated after 1,000 bootstraps. Models were assessed using goodness of fit (GoF) statistic. The GoFs for A-D are 0.630, 0.520, 0.622 and 0.718, respectively.