Relations between leaf and stem water potentials and stomatal conductance in three field-grown woody species

SummarySimultaneous measurements of stomatal conductance (gs), and leaf (ψleaf) and stem (ψstem) water potentials were conducted from 0900 hours to early afternoon on field-grown trees of apple, grapevine and nectarine which received different irrigation rates. The correlations of gs with ψstem (r2 = 0.85, 0.85, 0.79) was significantly higher than those with ψleaf (r2 = 0.51, 0.61, 0.37) for apple, grapevine and nectarine, respectively. The high correlation between gs and ψstem has been explained through a qualitative analysis of a water transport model which takes into account the control of gs by root signals (Tardieu and Davies, 1993). The model suggests that gs, ψleaf, root water potential, root-signal intensity, and transpiration rate are linked in a feedback mechanism which leads to the high correlation of gs and ψstem and causes it to be better than that with ψleaf.