Fig. 4.

Testing for a benefit in plant hydraulic design of a stomatal efficiency-safety trade-off. a contour plot shows modeled light saturated photosynthetic rate (A; units μmol m⁻² s⁻¹) for simulated species with combinations of maximum stomatal conductance (g_max) and sensitivity to stomatal closure (Ψ_gs50) under high water availability, i.e., soil water (Ψ_soil) of 0 MPa; species with higher g_max had higher A, whereas species with sensitive stomatal closure, i.e., higher (lower numerical values of) Ψ_gs50 had reduced A. b Modeled stem water potential (Ψ_stem; units: MPa) for these simulated species under low water availability, i.e., Ψ_soil of −1.2 MPa; species with higher g_max had steeper declines in Ψ_stem, whereas species with higher (lower numerical values of) Ψ_gs50 were protected from dehydration stress. The g_max vs. Ψ_gs50 trade-off for the 15 California species positioned these species in the optimal zone, with high enough g_max to achieve moderate to high values of A under high water availability, and sensitive enough stomatal closure (i.e., low enough numerical values of Ψ_gs50) to avoid hydraulic damage during drought. See “Methods” section for model description and parameterization, and Supplementary Fig. 3 for additional simulations, including of impacts on leaf water potential. Source data are provided as a Source Data file