Figure 7.

Definition of critical soil matric potential (ψ ^c _soil). It is indicated as the pink star in both subplots. (a) Relation between transpiration rate (E) and leaf xylem water potential (ψ _{leaf_x}) in wheat (Passioura, 1980). (b) Soil and root hydraulic conductance (K _soil and K _root) as a function of soil matric potential ψ _soil. Colour from dark blue to yellow in (a) stands for increasing E. The critical soil matric potential ψ ^c _soil is defined as the point where K _root equals K _soil was obtained by finding the intersection of fitted curves across K _root (K _{root_fit}) and K _soil (K _{soil_fit}) at the highest transpiration rate [Color figure can be viewed at wileyonlinelibrary.com]