Figure 1.

Generalized relationship between net CO₂ assimilation rate (A) and stomatal conductance (g_s). In many situations, the responses of A and g_s to environmental and internal conditions are such that the rates are often near the ‘break point’ on the relationship (indicated by arrow). Reductions in g_s below this point will reduce A by restricting CO₂ diffusion, and increases above it will bring only small increases in A, while causing large increases in transpiration.