Evaporation Rate, Leaf Water Potential and Stomatal Conductance in Lolium, Trifolium and Lysimachia in Drying Soil

Abstract

Van den Honert (1948) proposed that the flow of water through a plant, during transpiration, might be described by an Ohm's law analogue; although this simple theory attracted many adherents, it has not always been confirmed experimentally. Hailey et al. (1973) concluded that Ohm's law described water movement through plants when transpiration rates are similar to those expected in the field; however, their experimental plants were grown in solution culture. Contrasting results have sometimes been obtained with plants in soil (Hansen 1974) and, in practice, crop plants are grown in soil subject to cycles of drying and wetting. From the Ohm's law analogue of water transport through a plant or crop, the leaf water potential, P (Pa x 1O), depends on the soil water potential, -c (Pa x 1O), the rate of flow of water from the soil through unit plan area of foliage (the hydraulic flux density), F (g m-2 s1), and the hydraulic resistance to flow, Z (Pa x 105 m2 g's), between the sites of T and a,