Figure 4. Path diagrams summarizing 2 models of direct and indirect effects of temperature and CO₂ on alfalfa biomass.

Positive effects between variables are indicated by an arrow and negative effects are indicated by a filled circle. Standardized path coefficients are from the two general path models – blue coefficients are from a model that examined total leaf nitrogen (N) as a plant quality variable and red coefficients are from a model that examined saponins and sapogenins as plant quality variables. (A) Temperature and CO₂ effects on plant chemistry and the effects on alfalfa biomass. (B) A nested path model that demonstrates that the positive effects of natural enemies on plant biomass are mediated by decreased larval survivorship.