Estimation of stomatal conductance and stem water potential threshold values for water stress in olive trees (cv. Arbequina)

Abstract

Many irrigation strategies have been proposed in olive orchards to overcome both increasing water scarcity and competition for water with other sectors of society. However, threshold values of stomatal conductance (gs) and stem water potential (Ψstem) for use in designing deficit irrigation strategies have not yet been adequately defined. Thus, an experiment was conducted to determine gs and Ψstem thresholds for water stress in a super-intensive olive orchard (cv. Arbequina) located in Pencahue Valley (Maule Region, Chile) over three consecutive growing seasons. The experimental design was completely randomized with four irrigation treatments. The stem water potential (Ψstem) of the T1 treatment was maintained between − 1.4 and − 2.2 MPa, while the T2, T3, and T4 treatments did not receive irrigation from fruit set until they reached a Ψstem threshold of approximately − 3.5, − 5.0, and − 6.0 MPa, respectively. Stomatal conductance (gs), transpiration (Tl), net CO2 assimilation (An), and stem water potential (Ψstem) were measured fortnightly at midday. A significant nonlinear correlation between An and gs was used to establish different levels of water stress. Water stress was considered to be mild or absent when the gs values were greater than 0.18 mol m−2 s−1, whereas water stress was estimated to increase from moderate to severe as gs decreased significantly below 0.18 mol m−2 s−1. Similarly, water stress using Ψstem was determined to be mild or absent above − 2.0 MPa. Such categorizations should provide valuable information for maintaining trees well-watered in critical phenological phases.