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

摘要

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_1) 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_1 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_1 and VPD (R~2 = 0.74) than ambient temperature (R~2 = 0.58). Based on the regressions, estimates of Ψ_1 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_1 values ranged from -1.2 to -1.45 MPa. The values of Ψ_1 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.