Effects of Postharvest Water Deficits on the Physiological Behavior of Early-Maturing Nectarine Trees

The physiological performance of early-maturing nectarine trees in response to water deficits was studied during the postharvest period. Two deficit irrigation treatments were applied, moderate and severe, and these were compared with a control treatment (fully irrigated). Stem water potential and leaf gas exchange (net CO(2) assimilation rate, A(CO2); transpiration rate, E; and stomatal conductance, g(s)) were measured frequently. Drought avoidance mechanisms included a decrease in stomatal conductance, especially in the case of the severe deficit treatment, which also showed a strong dependence of A(CO2) on g(s). Intrinsic water-use efficiency (A(CO2)/g(s)) was more sensitive than instantaneous water-use efficiency (A(CO2)/E) as an indicator to detect water deficit situations in nectarine trees. However, in contrast to the results obtained for other deciduous fruit trees, a poor correlation was found between A(CO2)/E and A(CO2)/g(s), despite the important relation between E and g(s). A(CO2)/E was also weakly correlated with g(s), although this relationship clearly improved when the vapor pressure deficit (VPD) was included, along with g(s) as the independent variable. This fact reveals that apart from stomatal closure, E depends on the boundary layer conductance (g(b)), which is mediated by VPD through changes in wind speed. This suggests low values of the decoupling coefficient for this water-resilient species.