Soil and leaf water relations of differentially moisture- stressed honey mesquite (Prosopis glandulosa Torr)*

The objective of this study was to determine plant/soil water relations of honey mesquite (ProsopisglandulosaTorr.) following preconditioning to different levels of moisture stress. Moisture stress of 12 naturally occurring trees (mean height 3·2 m), located in north Texas, was manipulated through the use of drip irrigation and sub-canopy rain shelters. Pre-dawn leaf water potential and average daily stomatal conductance were greatest in irrigated trees and least in rain-sheltered trees on 27 June and 28 July 1986 after 1 and 2 months of stress preconditioning, respectively. Following a common irrigation of all trees (equiv- alent to 35-40 mm precipitation) on 28 June and 29 July, pre-dawn leaf water potential increased to similar levels in all trees within 1 day. Increase to maximum average daily stomatal conductance was delayed in moisture-stressed trees following the July watering, suggesting that moisture stress inhibited ability to respond to moisture availability. A positive relationship was found between soil moisture content and pre-dawn leaf water potential, and between soil moisture and average daily stomatal conductance. However, average daytime leaf water potential was unaffected by soil moisture content.