Influence of Soil Water Potential and Atmospheric Evaporative Demand on Transpiration and the Energy Status of Water in Plants¹

Abstract

Abstract Orchardgrass and tomato plants grown in a controlled environment chamber were subjected to varying soil moisture conditions. Constant atmospheric evaporative demand (AED) conditions were maintained by controlling temperature, relative humidity, light intensity, and hours of daylight while plants were carried through one series of soil moisture conditions. Then the AED was controlled at another set of values for a second series. Total plant water potential (ψ), osmotic potential (ψ a ), and relative turgidity were determined directly. Turgor potential was determined by the differences (ψ p ═ ψ – ψ a ) in leaf sections from plants grown under each set of soil moisture and atmospheric conditions. In addition, transpiration loss rates and soil water potentials (ψ s ) were measured daily. The total plant water potential (ψ), the osmotic potential (ψ a ), turgor potential (ψ p ), and transpiration losses from the two plant species were influenced by soil water potential (ψ s ) and AED. The effect was greater on ψ a than on either ψ or ψ p . The combined effect of AED and ψ s was more marked than either effect alone. High AED influenced plant moisture retention and transpiration more than low AED. The influence of the AED was more marked in moist soil (high ψ s ) than in drier soil.