Methods for Measuring Water Status and Reducing Transpirational Water Loss in Trees

Abstract

The growth and development of urban trees is probably influenced more by plant moisture than by any other single factor. In a time when water resources are becoming scarce, prudent use of existing water supplies becomes an important management decision for the arborist. Part of this decision process involves understanding the moisture requirements of urban trees and acquiring knowledge of the available methods for accurately estimating the water status of woody plant tissue. Relative water content, thermocouple psychrometry, and pressure equilibration are recommended as readily adaptable field techniques for measuring plant water relationships in urban trees. Monitoring sensitive changes in stem diameter, leaf temperature, and transpirational water loss are also suggested as potentially useful methods for estimating plant water status. The inefficiency of most plants in regulating internal moisture supplies can be attributed to the process of transpiration. Although numerous antitranspirants have been tested for their effectiveness in reducing transpirational water loss from leaves, current evidence indicates that the long-term effects of these substances on physiological activity (i.e., photosynthesis) may preclude their usefulness in the field except under special circumstances. The need exists to develop antitranspirant chemicals that reduce transpiration without appreciably affecting carbon dioxide exchange.