Water use efficiency and photosynthesis of Calamagrostis angustifolia leaves under drought stress through CO2 concentration increase

The effects of elevated CO2 concentration on photosynthetic gas exchange parameters and chlorophyll fluorescence parameters in leaves of Calamagrostis angustifolia seedlings under drought stress were studied through control of different CO2 concentrations (370 and 700 μmol·mol−1) with an artificial OTC climate chamber. The results demonstrated that: Under non-drought conditions, although the stomatal conductance (Gs) and transpiration rate (Tr) decreased slightly as the CO2 concentration increased, while the net photosynthetic rate (Pn) increased significantly, resulting in a significant increase in leaf water use efficiency (WUE). However, the effect of elevated CO2 concentration on PSII reaction center activity was insignificant under non drought conditions. Under severe drought stress, the amount of active reaction centers per unit area and the proportion of PSII absorbed light energy for photosynthetic electron transfer increased, while the proportion of PSII absorbed light energy for heat dissipation decreased, providing energy guarantee for effective fixation of CO2 as dark reaction. In conclusion, elevated CO2 concentration could improve the water use efficiency of C. angustifolia seedlings under normal water and drought stress, and the elevated CO2 concentration could improve the drought resistance ability of C. angustifolia seedlings through PSII function improvement under severe drought stress.