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

Summary

Simultaneous measurements of stomatal conductance (g_s), and leaf (ψ^leaf) and stem (ψ_stem) 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 g_s with ψ_stem (r² = 0.85, 0.85, 0.79) was significantly higher than those with ψ_leaf (r² = 0.51, 0.61, 0.37) for apple, grapevine and nectarine, respectively. The high correlation between g_s and ψ_stem has been explained through a qualitative analysis of a water transport model which takes into account the control of g_s by root signals (Tardieu and Davies, 1993). The model suggests that g_s, ψ_leaf, root water potential, root-signal intensity, and transpiration rate are linked in a feedback mechanism which leads to the high correlation of g_s and ψ_stem and causes it to be better than that with ψ_leaf.