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

Ahumada-Orellana, L., Ortega-Farías, S., Poblete-Echeverría, C., Searles, P. S.
Irrigation science 2019 v.37 no.4 pp. 461-467
Olea europaea, carbon dioxide, deficit irrigation, experimental design, fruit set, growing season, irrigation management, olives, orchards, phenology, stomatal conductance, trees, water potential, water shortages, water stress, Chile
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.