Effects of Elevated CO2 Concentration on Water Relations and Photosynthetic Responses to Drought Stress and Recovery during Rewatering in Tall Fescue

Water availability for plant growth is becoming increasingly limited, whereas rising atmospheric carbon dioxide concentration may have interactive effects with drought stress. The objectives of this study were to determine whether elevated CO 2 would mitigate drought-induced water deficit and photosynthesis inhibition and enhance recovery from drought damages on rewatering and to determine whether the mitigating effects during drought stress and the recovery in photosynthesis during rewatering by elevated CO 2 were the result of the regulation of stomatal movement or carboxylation activities in tall fescue ( Festuca arundinacea Schreb. cv. Rembrandt). Plants were grown in controlled-environment chambers with ambient CO 2 concentration (400 μmol·mol −1 ) or elevated CO 2 concentration (800 μmol·mol −1 ) and maintained well watered (control) or subjected to drought stress and subsequently rewatered. Elevated CO 2 reduced stomatal conductance ( g S ) and transpiration rate of leaves during both drought stress and rewatering. Osmotic adjustment and soluble sugar content were enhanced by elevated CO 2 . Elevated CO 2 enhanced net photosynthetic rate with lower g S but higher Rubisco and Rubisco activase activities during both drought and rewatering. The results demonstrated that elevated CO 2 could improve leaf hydration status and photosynthesis during both drought stress and rewatering, and the recovery in photosynthesis from drought damages on rewatering was mainly the result of the elimination of metabolic limitation from drought damages associated with carboxylation enzyme activities.