Seasonal responses of maize growth and water use to elevated CO2 based on a coupled device with climate chamber and weighing lysimeters

The increase in atmosphere carbon dioxide (CO₂) concentrations has been the most important environmental change experienced by agricultural systems. It is still uncertain whether grain yield of the global food crop of maize will remain unchanged under a future elevated CO₂ (eCO₂) environment. A coupled device with climate chamber and weighing lysimeters was developed to explore the water-related yield responses of maize to eCO₂. Two experiments were conducted via this device under eCO₂ (700 ppm) and current CO₂ (400 ppm) concentrations. Seasonal changes in multiple growth indicators and related hydrological processes were compared between these two experiments. The results showed that the eCO₂ effects were not significant on several indicators, i.e., the leaf carbon (C) content, nitrogen (N) content, chlorophyll content, C/N ratio, net photosynthesis rate, and leaf area index over the entire growing season (p > 0.05). Nevertheless, the transpiration rate (Tᵣ) significantly reduced during the seedling to filling stages but notably increased at the maturity stage due to eCO₂ (p < 0.05). Significant reduction in crop height (mean of 15.9%, p < 0.05) associated with notable increases in stem diameter (mean of 14.9%, p < 0.05) were found throughout the growing season. Dry matter per corncob at the final harvest decreased slightly under eCO₂ (mean of 7.7 g, p > 0.05). Soil water storage was not significantly conserved by the decline of Tᵣ except during the filling stage. Soil evaporation was likely promoted by eCO₂ that the total evapotranspiration changed little (1.2%) over the entire growing season. Although the leaf water use efficiency increased significantly at every growth stage (mean of 27.3%, p < 0.05), the grain yield and water productivity were not improved noticeably by eCO₂. This study could provide significant insight into predicting future crop yield and hydrological changes under climate change.