Abbreviations: ET, evapotranspiration; ψ, water potential; VPD, vapor pressure deficit. 1 UC Cooperative Extension, 733 County Center III Court, Modesto, CA 95355. This work supported in part by a grant from the California Prune Board. The cost of
Abbreviations: DSI, drought susceptibility index; ET, evapotranspiration; AT, canopy - air temperature; VPD, vapor pressure deficit. 1 Associate Professor, Dept. of Plant, Soil and Entomological Sciences. 2 Research Geneticist, U.S. Dept. of
, stress-degree-day; SW, short wave; TSD, temperature-stress-day; VPD, vapor pressure deficit; WI, withheld irrigation. 1 Postdoctoral Fellow. Current address: Dept. of Horticulture and Landscape Architecture, Washington State Univ., Pullman, WA 99164
potential in the liquid phase (from soil to leaf apoplast) and a difference in the water vapor pressure in the gas phase (from leaf to atmosphere). Therefore, VPD control was hypothesized to perform significant roles in reducing irrigation demand and
). Saturation vapor pressure (e sat ) was computed from T a using Murray's equation ( Murray, 1967 ). Vapor pressure deficit (VPD) was computed from the difference between saturated and actual vapor pressure (e a ) at T a . All temperatures other than T a were
pedicels) is usually described by Fick’s law: where F (grams per second) is the measured rate of transpiration, A (square meters) the organ’s surface area, and ΔC (grams per cubic meter) the difference in water vapor concentration between the inside
as light intensity and RH ( Lu et al., 2017 ; Marchin et al., 2016 ). RH is the ratio of the amount of water vapor in the air relative to the amount of water vapor that would be present at saturation, which also influences many life processes such as
density of trees and several tree leaf characteristics, including the color, texture, and thickness, might affect the effectiveness of cooling. In addition, background microclimate conditions, including the intensity of solar radiation, vapor pressure of
Abstract
Dry air is a mixture of nitrogen (about 78%) and oxygen (about 21%), with argon, carbon dioxide and other minor constituents making up the remaining 1%. Moist air is defined as a two-component mixture of dry air and water vapor. The amount of water vapor in air can be highly variable, ranging from 0 (dry air) to a maximum that depends upon temperature and pressure. The term “humidity” relates to the presence of water vapor in air but, depending upon its particular usage, may be used to express either the absolute quantity or the relative amount of water vapor in a moist air mixture.
desiccation injury. Kozlowski (1976) stated that such injury occurs when a large vapor pressure deficit or solar radiation load at low temperatures results in a rate of water loss from aboveground parts of the plant that exceeds the rate of water uptake and