Relationships among Ambient Temperature and Vapor Pressure Deficit and Leaf and Stem Water Potentials of Fully Irrigated, Field-Grown Grapevines

Abstract

Four Vitis vinifera L. cultivars grown at five locations throughout California were studied to determine the relationships among temperature and vapor pressure deficit (VPD) and leaf water potential (Ψ_l) measured under clear skies at midday (solar noon) or in some instances midmorning to midafternoon. Stem water potential (Ψ_stem) was also measured on several occasions. Vines were irrigated at 100% or greater of measured or estimated vineyard evapotranspiration, and deficit or nonirrigated vines were included for comparison. Temperature and VPD were determined at the time of measurement. The highest and lowest values of Ψ_l measured on well-watered grapevines were −0.51 and −1.15 MPa, respectively. Leaf and stem water potentials were linearly related to VPD and ambient temperature. The coefficient of determination was greater for the relationship between Ψ_l and VPD (R² = 0.74) than ambient temperature (R² = 0.58). Based on the regressions, estimates of Ψ_l at a VPD of 2 and 5 kPa for fully irrigated grapevines would be −0.65 and −0.89, respectively, while those of Ψ_stem at the same VPDs would be −0.37 and −0.57 MPa, respectively. Leaf water potential of water-stressed vines was less responsive to VPD or temperature when Ψ_l values ranged from −1.2 to −1.45 MPa. The values of Ψ_l and Ψ_stem as a function of VPD or temperature could serve as baselines indicating whether grapevines are fully irrigated or not water stressed under the environmental conditions found in semiarid grapegrowing regions.