ISHS Acta Horticulturae 470: II International Symposium on Pistachios and Almonds
WATER STRESS RESPONSES OF ALMOND [PRUNUS DULCIS (MILL.) WEBB.] TREES UNDER FIELD CONDITIONS |
| Authors: | K. Shackel, S. Gurusinghe, D. Kester, W. Micke |
| Keywords: | pressure chamber irrigation growth stomatal conductance |
| Abstract:
We have used the measurement of midday stem water potential as an index of water stress in almond and other fruit trees, and have found it to be a particularly useful measure that combines the influences of plant, soil and atmospheric conditions on overall plant performance. The midday stem water potential exhibited by almonds under wet soil conditions appears to have the same linear relation to midday atmospheric vapor pressure deficit (VPD) as that previously published for prunes [Stem Water Potential (MPa) = -0.41 - 0.12*VPD (KPa)]. After two years of growth under contrasting irrigation regimes, there was a strong linear relation of overall tree size (as measured by trunk cross-sectional area) to average midday stem water potential. Significant tree-to-tree differences in both tree size and average midday stem water potential also occurred within an irrigation regime, indicating that individual tree or site differences can have a major influence on the overall degree of water stress experienced by an almond tree under any particular irrigation regime. Early tree yield was also associated with overall tree size, indicating that growth reductions caused by water stress early in the life of an almond orchard may also have important economic effects. On a shorter term basis, midday leaf conductance was also very responsive to midday stem water potential, and exhibited an apparent threshold of about -1.0 MPa for the beginning of stomatal closure with stress. During the progress of water stress over the growing season, irrigation treatment effects on midday stem water potential were apparent before any treatment effect could be seen in midday leaf conductance. On a seasonal average basis, a very similar relation of both conductance and growth to stem water potential occurred, indicating that the physiological responses of almond to water stress may be closely related to plant water status as measured by midday stem water potential. | |
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