Effect of elevated carbon dioxide and water stress on gas exchange and water use efficiency in corn

摘要

CO sub(2) has been predicted to increase in the future, and thus leading to possible changes in precipitation patterns. The objectives of this study were to investigate water use and canopy level photosynthesis of corn plants, and to quantify water use efficiency in corn plants under two different CO sub(2) levels combined with four different water stress levels. Corn plants were planted in sunlit plant growth chambers and a dayight temperature of (28/18 degree C) was applied. From 21 days after emergence (DAE), the eight treatments including two levels of carbon dioxide concentrations (400 and 800 mu mol mol super(-1)) and four levels of water stress (well-watered control, "mild", "moderate", and "severe" water stress) treatments at each CO sub(2) level were imposed. Height, number of leaves, leaf lengths, and growth stages of corn plants were monitored from nine plants twice a week. Corn plants were separately collected, dried, and analyzed for the biomass accumulation at 21 and 60 DAE. Soil water contents were monitored by a time domain reflectometry (TDR) system (15 probes per chamber). The "breaking points" (changes from high to low rates of soil water uptake) were observed in the bottom of soil depth for the water stressed conditions, and the "breaking points" under ambient CO2 appeared 6-9 days earlier than under elevated CO sub(2). Although approximately 20-49% less water was applied for the elevated CO sub(2) treatments than for ambient CO sub(2) from 21 DAE, higher soil water contents were recorded under elevated CO sub(2) than under ambient CO sub(2). However, corn growth variables such as height, leaf area, and biomass accumulation were not significantly different in CO sub(2) or water stressed treatments. This result may be explained by considering that significant differences in canopy level gross photosynthesis among the water stress treatments was observed only toward the end of the experiment. The higher soil water contents observed under elevated CO sub(2) resulted mainly from less water use than under ambient CO sub(2). WUE (above ground biomass per water use since 21 DAE) at the final harvest was consistently higher and varied with a smaller range under elevated CO sub(2) than under ambient CO sub(2). This study suggests that less water will be required for corn under high-CO sub(2) environment in the future than at present.