Stem-water potential as a sensitive indicator of water stress in prune trees (Prunus domestica L. cv. French)
McCutchan, H. | Shackel, K.A.
The relative sensitivity of plant- and soil-based measures of water availability were compared for prune trees subjected to a range of irrigation regimes under field conditions. Over the growing season, leaf- and stem-water potentials measured at midday exhibited clear differences between frequently irrigated trees and unirrigated trees that were growing on stored soil moisture. Stem water potential variable than leaf water potential, and the daily variability in stem water potential was closely related to daily variability in evaporative demands, as measured by vapor pressure deficit (VPD). As a result of lower variability, stem water potential reflected the small stress effect of a moderate, 50% soil moisture depletion irrigation interval, whereas leaf water potential did not. The relation between soil water content and estimated orchard evapotranspiration (ET) was influenced by local differences in soil texture within the experimental plot. The relation between stem water potential and ET, however, was not influenced by soil texture and, in addition, was very similar to the relation between stem water potential and leaf stomatal conductance. Both relationships indicated that a 50% reduction in leaf and canopy level water loss characteristics was associated with relatively small reductions (0.5 to 0.6 MPa) in stem water potential. Stem water potential appears to be a sensitive and reliable plant-based measure of water stress in prune and may be a useful tool for experimental work and irrigation scheduling.
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