Figure 7.
Simulated response of mid-day operating stomatal conductance (as a percentage of maximum for hydrated leaves) and leaf water potential to drying soil at VPD of (a,b) 1 kPa and (c,d) 3 kPa, for a C3 species and C4 species with identical plant hydraulic conductance (Kplant), for a simulated C4 species with double the Kplant, and for a simulated C4 species with half the Kplant (corresponding to its value of gs being approximately half that of the C3 species). Note that the C4 species maintains stomatal opening into drier soil and higher VPD than the C3. Increasing the Kplant improves this ability in the C4 species, whereas reducing the Kplant by half leads to very rapid decline of gs at high VPD or in a dry soil. (a–d) Dashed line, C3; black solid line, C4; light grey solid line, C4, 2 × Kplant; dark grey solid line, C4, 0.5 × Kplant.