Water Transport in Wheat Plants in the Field¹

Most previous studies of water transport in crops have been based on simplified models of plant anatomy and canopy transpiration. Usually changes in the water potential of a particular leaf have been related to the water loss from the whole canopy. We present a more detailed analysis of plant water transport which accounts for the spatial distribution of water flows and transpiration losses throughout the canopy, and use it to estimate flow resistances in different segments of the pathway. Micrometeorological measurements of the flux densities of water vapor in the canopy were used to infer water fluxes through roots, stem sections, leaves, and ears of wheat plants ( Triticum aestivum L. ‘Heron’) in the field. Simultaneous measurements of soil‐ and leaf‐water potentials permitted calculation of flow resistances in roots, stems, and leaves. There were no significant differences in resistances between an irrigated and a dryland crop, although the patterns of stem flow differed markedly. The resistance of the root system of an individual tiller was (1.00 ± 0.37) × 10' bar sec cm ‐3 and the resistance/unit length of stems and leaves was (1.59 ± 0.19) × 10 3 bar sec cm ‐4 . These large plant resistances may often be as important in determining leaf water potentials as the transmission resistance of the soil. The study shows clearly how the water loss from one part of the canopy influences the development of water potentials in other parts and points up the difficulties of simplified transport models.