Four modern cultivars of winter wheat (Triticum aestivum L.) were grown under elevated ozone concentration (E-O3) in fully open-air field conditions in China for three consecutive growth seasons from 2007 to 2009. Results indicated that a mean 25% enhancement above the ambient ozone concentration (A-O3, 45.7 p.p.b.) significantly reduced the grain yield by 20% with significant variation in the range from 10% to 35% among the combinations of cultivar and season. The varietal difference in the yield response to E-O3 became nonsignificant when the anova was done by omitting one cultivar which showed unstable response to E-O3 among the seasons. The reduction of individual grain mass accounted mostly for the yield loss by E-O3, and showed significant difference between the cultivars. The response of relative yield to E-O3 was not significantly different from those reported in China, Europe and India on the basis of experiments in open-top chambers. Our results thus confirmed the rising threat of surface O3 on wheat production worldwide in the near future. Various countermeasures are urgently needed against the crop losses due to O3 such as mitigation of the increase in surface O3 with stricter pollution control, and enhancement of the wheat tolerance against O3 by breeding and management.
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