| Although high temperature and drought frequently occur concurrently during maturation and greatly reduce yield of wheat (Triticum aestivum L.), their effects are usually studied individually. Knowledge of interactions between the stresses is needed to distinguish their direct and indirect effects and to understand their synergistic effects that might exacerbate injury. Our objectives were to compare the effects of high temperature and drought or osmotic stresses and to ascertain their interactions on photosynthesis, productivity, and water relations of wheat. 'Len' spring wheat plants were uniformly grown in either silt-loam soil or Hoagland solution in a greenhouse until anthesis. These plants were subjected to day/night temperatures of 15/10, 25/20, or 35/30{dollar}spcirc{dollar}C and moisture regimes of either no drought or drought and no osmotic stress or osmotic stress in controlled environment chambers. Plant photosynthesis, leaf area and mass, relative water content, and water potential and its components were measured at weekly intervals. High temperature hastened the decline in photosynthetic rate and viable leaf area during maturation. It decreased shoot and grain mass, kernel weight, and soluble sugar content at maturity. Additionally, high temperature reduced water use efficiency, decreased relative water content, and plant water potential, and its components. Low temperature effects were opposite of high temperature. Drought or osmotic stress increased stomatal resistance and decreased photosynthesis, viable leaf area, shoot mass, grain mass, kernel weight, soluble sugar content, and all water status values, and enhanced water use efficiency. Effects of drought were much more pronounced at high temperature than at low temperature. Moreover, low temperature enabled the plants subjected to osmotic stress to adjust osmotically because of production of photosynthates. High temperature and drought interact because of complementary effects on photosynthesis, water relations, and productivity and beneficial effects of low temperature on osmotic adjustment to stress. Wheat can tolerate considerable drought or osmotic stress if the temperature is favorable because of direct effects that maintain photosynthesis and indirect effects that minimize injury from drought or osmotic stress. Increasing resistance of wheat at high temperature might improve its adaptation to regions with elevated temperature and either ample or deficient moisture. |
