Effects of elevated atmospheric CO₂ concentration and shading onleaf light utilization and yield of wheat

CO₂ and light energy are dynamic substrates of plant photosynthesis. Changes in CO₂ concentration and light energy intensity lead to corresponding changes in the characteristics of plant photosynthesis and growth. It was therefore critical to study the effect of atmospheric CO₂ concentration and light intensity on plant photosynthesis which could foster further understanding of the response of terrestrial ecosystem to global climate change. This study analyzed the elevated atmospheric CO₂ concentration (760 μmol·mol^-1) and shading effects on wheat light utilization and yield. In the study, CO₂ concentrations and light intensity were set up and measures were taken on photosynthetic gas exchange parameters, light-photosynthetic response curves and yield. The relationship between light intensity and light use efficiency was analyzed and then elevated atmospheric CO₂ concentration (760 μmol·mol^-1) and shading effects on wheat photosynthesis and yield determined. Result showed that compared with normal CO₂ concentration, net photosynthetic rate (P_n), maximum net photosynthetic rate (P_nmax), light saturation point (LSP) and light compensation point (LCP) of wheat leaves increased significantly under elevated atmospheric CO₂ concentration. However, under shading conditions, P_nmax, LSP and LCP decreased. Under normal and elevated atmospheric CO₂ concentrations, dark respiration rate (R_d) of wheat leaves decreased significantly. However, shading and elevated atmospheric CO₂ concentration had no significant effect on R_d. Apparent quantum yield (AQY) of wheat leaves increased significantly with increasing atmospheric CO₂ concentration. Conversely, the effect of shading on AQY changed with changes in atmospheric CO₂ concentration. While shading significantly increased AQY under elevated atmospheric CO₂ concentration, it significantly decreased AQY under normal CO₂ concentration. While plant height and spike length increased significantly under elevated atmospheric CO₂ concentration and shading, grain number, grain weight per spike and 1000-grain weight decreased significantly. Because of changes in photosynthetic characteristics and limitations in light intensity, wheat leaf respiration increased under elevated atmospheric CO₂ concentration and shading conditions. This resulted in the decline of P_n, which limited dry mass accumulation and grain yield formation.