Response of wheat to combined high temperature and osmotic stresses during maturation. Plant photosynthesis and productivity

High temperature and drought are usually investigated singly, although they frequently occur simultaneously in nature.Our objectives were to compare effects of high temperature and osmotic injury on photosynthesis and productivity of wheat during grain filling and to ascertain interactions between the combined stresses. Plants (cv. Len) were grown uniformly until anthesis, and treatments of 15/10, 25/20, and 35/30oC and -0.01 or -0.41 MPa were imposed until maturity. Photosynthesis, leaf area, and plant mass were measured at weekly intervals. The decline in photosynthesis and rise in stomal resistance during maturation were slowed by low temperature and speeded by high temperature, and damage from osmotic stress increased substantially with rise in temperature. Viable leaf area persisted longer and was diminished less by osmotic stress under low temperature than under high temperature. Vegetative and grain masses at maturity were increased by low temperature and were reduced most by osmotic stress with high temperature. The results demonstrate that high temperature and osmotic stress reduce photosynthesis and productivity and interact synergistically to accentuate injury. Wheat can tolerate considerable osmotic stress if the temperature is favorable because of a direct effect that maintains photosynthesis and an indirect effect that minimizes injury from osmotic stress.