Seasonal responses of maize growth and water use to elevated CO_2 based on a coupled device with climate chamber and weighing lysimeters

摘要

The increase in atmosphere carbon dioxide (CO_2) 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 CO_2 (eCO_2) environment. A coupled device with climate chamber and weighing lysimeters was developed to explore the water-related yield responses of maize to eCO_2. Two experiments were conducted via this device under eCO_2 (700 ppm) and current CO_2 (400 ppm) concentrations. Seasonal changes in multiple growth indicators and related hydrological processes were compared between these two experiments. The results showed that the eCO_2 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 (TV) significantly reduced during the seedling to filling stages but notably increased at the maturity stage due to eCO_2 (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 eCO_2 (mean of 7.7 g, p ＞ 0.05). Soil water storage was not significantly conserved by the decline of T_r except during the filling stage. Soil evaporation was likely promoted by eCO_2 that the total evapotranspiration changed little (1.2%) over the entire growing season. Although the leaf watet 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 eCO_2. This study could provide significant insight into predicting future crop yield and hydrological changes under climate change.