Wheat yield response to elevated O 3 concentrations differs between the world's major producing regions.

Ground-level ozone (O ₃ ) concentration is rising in Asia, which accommodates the world's top-two wheat producers (China and India). Because wheat is among the species of high O ₃ sensitivity, yield loss due to rising O ₃ in Asia is a major threat to global wheat supply. We estimated the relationships between O ₃ dose on AOT40 (accumulated daytime O ₃ concentrations above 40 ppb for 90 days) and relative wheat yield for four wheat producing regions: China, India, Europe and North America using results of O ₃ elevation experiments conducted therein. When compared on the same AOT40, the estimated yield loss was greatest in China followed by India, Europe, and North America in this order. In China, Europe and North America, the yield loss was primarily due to the reduction of single grain weight, whereas in India reduction of the number of grains contributed more to the yield loss than single grain weight. The greater response of the number of grains to O ₃ in India can be explained by the earlier start of O ₃ elevation, but the seasonal change in O ₃ concentrations cannot explain the lower yield loss in North America than China and India. Referring to the past reports of lower yield sensitivity to O ₃ in older cultivars, we compared the year of release of cultivars between the regions. In North America, they used cultivars released in 1980s or earlier, whereas in China they used cultivars released in 2000s. In Europe and India, most cultivars were released between those in North America and China. The difference in cultivars could therefore be a cause the differential yield response among the regions. We argue that the O ₃ -induced yield loss should be quantified using the dose-response relationships for each region accounting for the effects of seasonal change in O ₃ concentrations, cultivars and climate on the yield response.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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