Plant–Water Relations

Abstract

Plant–water relations concern how plants control the hydration of their cells, including the collection of water from the soil, its transport within the plant and its loss by evaporation from the leaves. The water status of plants is usually expressed as ‘water potential’, which has units of pressure, is always negative, and in simple form is the algebraic sumofthe hydrostatic pressure and the osmotic pressure of water. Flow of water through plant and soil over macroscopic distances is driven by gradients in hydrostatic pressure. Over microscopic distances (e.g. across semipermeable membranes) it is driven by gradi- ents in water potential. Evaporation of water from leaves is primarily controlled by stomata, and if not made good by the flow of water from soil through the plant to the leaves, results in the plants wilting. Resistances to this flow are still not well understood.