Evaluation of the quantitative relation between diurnal fluctuations in stem radius and water stress of cotton plants under field conditions

Abstract

Radical changes of cotton plant stems were monitored throughout the 1969 and 1970 crop seasons under field conditions using linear variable displacement transducers. The absolute amount of stem contraction from the 0600 hr condition was closely related to the relative water content of the cotton leaves during stress cycles. The water potential of cotton leaves was closely related to the amount of stem contraction during the desorption phase of the stress cycle. Hysteresis confounded the relation during the absorption or recovery phase of the stress cycle. The data indicate that the degree of cotton stem contraction is directly related to the water potential gradient established in the water conducting tissues of the stem due to an imbalance between transpiration and absorption rates. Plant water stress, in term of radical change measurements, was closely associated with changing soil moisture tension and solar radiation conditions. A response in the radical change measurement was consistently detected within 8 to 10 minutes of a sudden change in radiation flux density due to the passing of a cloud, thus indicating that plant water stress is very dynamic, changing rapidly with changing environmental conditions. The rate of radical change vs cumulative radiation up to midafternoon increased with increasing mean soil moisture tension. It is postulated that these rates (radical change (mm) per ly incident radiation) reflect the imbalance between transpiration and absorption thus provide a measure of the capacity of the soil to supply water to the roots under the existing atmospheric conditions..