Physiological responses of 'Arbequina' olive trees to summer deficit irrigation

Most of the olive growing areas in the Mediterranean region are characterized by scarce water resources, especially in summer. This lack of water negatively affects the physiological development of the plant and thus its productivity. However, olive tree seems to be less sensitive to water stress during summer. To evaluate the physiological responses of olive trees to water stress during this period three deficit irrigation treatments were applied. Control trees (CON) were irrigated to maintain the root zone close to field capacity. Two severe water deficit treatments were applied during summer by irrigating: i) DI-J irrigating 30% CON in July (1st period), and ii) DI-A irrigating 30% CON in August (2nd period). Moderate water deficit was applied from July to August (1st and 2nd periods) by irrigating 50% CON in DI-JA. Midday stem water potential (Psi s) and stomatal conductance (g) were measured during the irrigation period. Relative extractable water (REW) was determined from soil water content. Vapour pressure deficit (VPD) and ETo were calculated. The irrigation treatments modified midday stomatal conductance (g) during summer, in response to the different amounts of water applied. When irrigation was reestablished these differences between treatments disappeared, showing a high capacity of the olive tree for a use of water when this is available. In moderate stresses trees (Psi s>-1.5MPa) g was linearly and curvilinearly related to REW and VPD, respectively. Only when water atmospheric demand was lower than 5.5 mm d(-1), g was significantly correlated with Psi s.