Grapevine trunk and shoot diameter microvariations and trends as indicators of water potential
2004
Ton, Y. | Kopyt, M.
Correlation between stem water potential and two indicators of trunk and shoot diameter behavior, daily maximum and daily contraction amplitude (DCA), was examined on Chardonnay vines during the 2001-2002 seasons at Golan Heights (Israel). The DCA is commonly used as a measure of water deficit in plants and even for calculating leaf water potential. Calculation of the difference between predawn maximum and daytime minimum is the common method for determining DCA. However, in dry conditions, water reserves in plants are not completely replenished at night, resulting in gradual depression of predawn maximum. This resulted in a poor correlation found between DCA and stem water potential during periods of soil water deficit and air drought. The alternative method for determining DCA is based on using the potential maximum diameter baseline (PMDB) instead of the actual predawn maxima. The recalculation of DCA in relation to PMDB changed the coefficient of determination - R2 from almost negligible level to about 0.8. In general, the depression of daily trunk diameter maximum corresponds to predawn water status while the modified DCA correlates with the stem water potential. The depression of daily maximum seems to be a good alternative to a predawn water potential measurement, which is not used in commercial practice. In its part, the midday water potential, which is actually a concession to a cumbersome predawn measurement, represents the daytime transpiration demand rather than the available water content in the soil.
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