The usefulness of stomatal response as an indicator of the onset and development of water stress was studied over five seasons in field-grown wheat (Triticum aestivumL.) and soybeans (Glycine maxL. Merr.). With the onset of water stress, stomatal diffusive resistance (rs) showed a clear increase which coincided with changes in other accepted indicators, such as leaf water potential (#x3C8;) and soybean leaf movements. Well-watered plants exhibited low variability in midday values of rs throughout the season and between plants, making changes easy to detect and a well-watered control unnecessary. Water stress was clearly manifested by an increase in rs control values and an increase in variability between measurements. Both abaxial and adaxial leaf stomata increased rs in. response to water stress, with the former more sensitive in wheat and the latter more sensitive in soybeans. Stomatal response in wheat, but not in soybeans, changed with water-stress preconditioning by staying open to lower values of ? in a subsequent stress. The sensitivity of stomatal response to water stress, ease of measurement with the steady state porometer, consistency of rs values, low variability between well-watered plants, and the lack of need for a control, make rs a potentially useful and reliable plant indicator of crop water stress.
展开▼
