Stomatal Control and Hydraulic Conductivity in 'Manzanilla' Olive Trees under Different Water Regimes

We studied the response of leaf water potential (psi(l)), stomatal conductance (g(s)), leaf specific hydraulic conductivity (K-l) and percentage loss of hydraulic conductivity (PLC) in current-year shoots of 40-year-old 'Manzanilla' olive trees under three water treatments: Rainfed, in which rainfall was the only source of water; FAO, in which the trees were under localized irrigation to replace crop water demand; Pond, in which the whole root zone of the trees was maintained under non-limiting soil water conditions throughout the irrigation season. In the FAO trees, some roots were left in drying soil during the irrigation season. Results suggest near-isohydric behavior of olive trees. FAO trees maintained psi(l) values similar to those of Pond trees by increasing stomatal closure. In Rainfed trees, g(s) values were smaller than in the irrigated trees, but stomatal closure did not prevent psi(l) values from falling below those of the irrigated trees, likely because of the dramatic decrease in soil water content observed in the Rainfed treatment. Values of K-l and PLC showed no differences between treatments throughout the irrigation season. During that period, the PLC values ranged from 38% to 50%, which shows that even the well-irrigated Pond trees were unable to maintain their hydraulic efficiency, likely because of the high atmospheric demand in the area.