Figure 2. Structural equation model of the effect of temperature on AMF colonization and plant biomass.

We tested three a priori models that included either soil and plant nitrogen, soil and plant phosphorus, or soil and plant N:P ratios. Each box represents a variable in the model, while each arrow represents a predicted direct effect of one variable on another. A series of connected arrows through multiple variables represent indirect effects. The direct effect plus all the indirect effects of one variable on another is referred to as the total effect.