A meta-analysis of responses of wheat yield formation to elevated ozone concentration

The meta-analysis method was applied to quantitatively investigate effects of the elevated ozone concentration (O₃]) on chlorophyll concentration, gas exchange and yield components of wheat. There were 39 effective references through Web of Science (ISI, USA) and Chinese journal full-text database (CNKI, China). The results of meta-analysis indicated that elevated O₃] decreased grain yield, grain weight, grain number per ear, ear number per plant and harvest index by 26%, 18%, 11%, 5% and 11%, respectively, relative to ambient air. The decrease in leaf physiological characters was much greater than that in yield when wheat was expose to elevated O₃], while light-saturated photosynthetic rate (Asat), stomatal conductance (Gs) and chlorophyll content (Chl) decreased by 40%, 31%, and 46%, respectively. The responses to elevated O₃] between spring wheat and winter wheat were similar. Most of the variables showed a linear decrease trend with an increase of O₃]. The most significant decrease for Asat, Gs and Chl was found in grain filling stage. Elevated CO₂] could significantly ameliorated or offset the detrimental effects caused by elevated O₃]. Supported by National Natural Science Foundation of China (Grant No. 30670387), Eco-Frontier Fellowship of the Ministry of Environment, Japan (Grant No. 07-C062-03) and Ministry of Science and Technology of People’s Republic China with 973 Project (Grant No. 2002CB410803)