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 ([CO2]). 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 [CO2] 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.