Leaf Water and Turgor Potential Threshold Values for Leaf Growth of Wheat 1

Environmental factors affecting leaf growth must be understood for accurate predictions of yield by crop modeling. Water is one of the most important of these factors. The effect of water deficits on the relationships between leaf elongation and leaf water and turgor potentials was investigated on wheat ( Triticum aestivum L.) grown under field conditions on a Rhodic Paleustalf on the Highfeld Plateau of the Republic of South Africa. Leaf growth rates of water stressed and nonstressed wheat were measured, and corresponding values of leaf water, osmotic and turgor potentials obtained using thermocouple psychrometers. Water stress resulted in a reduced growth rate and a lower total cumulative growth. The growth curve was made up of two phases, an initial phase of both lamina and leaf sheath elongation, and a second phase of leaf sheath elongation alone. The different relationships between growth rate and midday leaf turgor potential in the two phases indicated leaf sheath elongation to be more sensitive to stress than lamina elongation. The water‐stressed treatment had a lower water potential threshold value for elongation of ‒2571 kPa compared with ‒1671 kPa for well‐watered plants. Turgor potential threshold values for elongation in the stressed plants were also lower by 197 kPa for the phase of leaf lamina and sheath elongation, and by 488 kPa for the phase of sheath elongation alone. Stress acclimation apparently occurred by osmotic adjustment to maintain turgor potentials necessary for elongation.