Impact of elevated ozone concentration on growth, physiology, and yield of wheat (Triticum aestivum L.): a meta‐analysis

We quantitatively evaluated the effects of elevated concentration of ozone (O 3 ) on growth, leaf chemistry, gas exchange, grain yield, and grain quality relative to carbon‐filtered air (CF) by means of meta‐analysis of published data. Our database consisted of 53 peer‐reviewed studies published between 1980 and 2007, taking into account wheat type, O 3 fumigation method, rooting environment, O 3 concentration ([O 3 ]), developmental stage, and additional treatments such as drought and elevated carbon dioxide concentration ([CO 2 ]). The results suggested that elevated [O 3 ] decreased wheat grain yield by 29% (CI: 24–34%) and aboveground biomass by 18% (CI: 13–24%), where CI is the 95% confidence interval. Even in studies where the [O 3 ] range was between 31 and 59 ppb (average 43 ppb), there was a significant decrease in the grain yield (18%) and biomass (16%) relative to CF. Despite the increase in the grain protein content (6.8%), elevated [O 3 ] significantly decreased the grain protein yield (−18%). Relative to CF, elevated [O 3 ] significantly decreased photosynthetic rates (−20%), Rubisco activity (−19%), stomatal conductance (−22%), and chlorophyll content (−40%). For the whole plant, rising [O 3 ] induced a larger decrease in belowground (−27%) biomass than in aboveground (−18%) biomass. There was no significant response difference between spring wheat and winter wheat. Wheat grown in the field showed larger decreases in leaf photosynthesis parameters than wheat grown in < 5 L pots. Open‐top chamber fumigation induced a larger reduction than indoor growth chambers, when plants were exposed to elevated [O 3 ]. The detrimental effect was progressively greater as the average daily [O 3 ] increased, with very few exceptions. The impact of O 3 increased with developmental stages, with the largest detrimental impact during grain filling. Both drought and elevated [CO 2 ] significantly ameliorated the detrimental effects of elevated [O 3 ], which could be explained by a significant decrease in O 3 uptake resulting from decreased stomatal conductance.