Elevated CO2 improves the performance of bread wheat under drought stress through better physiological responses and grain yield

This study aimed to explore the effects of elevated CO2 (e[CO2]) on wheat performance under drought stress, while investigating the role of eco-physiology, carbohydrate metabolic and antioxidant enzymes to predict the grain yield. Wheat genotype Lianmai6 was grown under ambient (400ppm) and elevated (800ppm) CO2 concentrations, with subsequent exposure to drought stress prior to anthesis. Leaf parameters, including photosynthetic rate (An), stomatal conductance (Gs), and transpiration rate (E), were significantly declined under drought. Grain yield parameters were adversely affected by drought stress, while An and water use efficiency (WUE) and yield traits increased under e[CO2]. Notably, the activities of certain carbohydrate metabolic enzymes were increased in sink tissues but reduced significantly in source tissues under drought conditions. However, activities phosphoglucomutase (PGM and phophoglucoisomerase (PGI) were increased in source tissues under the combined effect of drought and e[CO2]. Total antioxidant potential (TAP) decreased in both leaf and spike under drought conditions, yet increased significantly under e[CO2]. These findings suggest that e[CO2] can enhance CO2 assimilation by boosting antioxidant potential and facilitate increased supply of photosynthates through enhanced activities of various carbohydrate metabolic enzymes, ultimately the better grain yield. These findings could elucidate the partial mechanism of better grain yield in bread wheat under combined effect of e[CO2] and drought stress.