Effects of elevated CO₂ concentration and different water conditions on winter wheat growth and water use

Elevated CO₂ concentration has been the main cause of climate change and has gained considerable attention due to its important impacts on crop growth and yield formation. Winter wheat, a major food crop in China, is mainly cultivated in the arid and semiarid regions of the country. It is therefore critical to study the growth and water use of winter wheat under different water and CO₂ conditions. In this study, winter wheat was grown in a pot experiment in closed chambers subjected to two concentrations of CO₂ (396.1±29.2) μmol·mol^-1 (A) and (760.1±36.1) μmol·mol^-1 (E) and two soil water contents 70% 80% (sufficient) and 50% 60% (drought) of field capacity. Plant growth, aboveground biomass, grain yield and water use efficiency (WUE) at different stages were analyzed. The results showed that although elevated CO₂ had no significant effect on plant height and ear length, it respectively increased biomass by 28.6% and 18.6% under sufficient and drought water conditions. Elevated CO₂ also respectively increased grain number and grain yield by 24.3% and 32.6% under sufficient water conditions and by 15.5% and 22.6% under drought conditions. Elevated CO₂ showed no significant effect on the 1000-grain weight. Elevated CO₂ increased evapotranspiration respectively by 8.5% and 4.6% under sufficient and drought water conditions. It also respectively increased population WUE by 17.7% and 13.7% and grain WUE by 24.8% and 17.1% under sufficient and drought water conditions. Elevated CO₂ increased Pn by 15.6% and 12.9%, decreased Gs by 22.7% and 18.2% and Tr by 8.9% and 7.5% under sufficient and drought water conditions, respectively. Chlorophyll and water potential also increased under elevated CO₂. There was a higher increase in water potential (7.7%) under sufficient water conditions while chlorophyll increased respectively by 7.5% and 3.8% under sufficient and drought water conditions. The results suggested that the effect of elevated CO₂ on winter wheat growth, yield and WUE also depended on water conditions. The positive effects exceed the negative effects under sufficient water conditions. Grain yield improvement under elevated CO₂ and was mainly driven by increased grain number.