Current surface ozone concentrations significantly decrease wheat growth, yield and quality.

Tropospheric ozone is known to adversely affect crops and other vegetation. Most studies have focussed on the effects of elevated ozone levels vs. present ambient. We investigated the effect of present ambient surface ozone (O3) concentrations vs. preindustrial on a range of agronomically important response variables in field-grown wheat, using results from 33 experiments (representing 9 countries, 3 continents, 17 cultivars plus one set of 4 cultivars) having both charcoal filtered (CF) and non-filtered (NF) air treatments. Average filtration efficiency was 62%, reducing the O3 concentration from 35.6±10.6SDppb in NF to 13.7±8.8SDppb in CF. Average CF concentrations were in the range of levels believed to represent pre-industrial conditions, while NF concentrations were 7% lower than in the ambient air at plant height on the experimental sites. NF had significant (p<0.05) negative effects compared to CF on grain yield (-8.4%), grain mass (-3.7%), harvest index (-2.4%), total above-ground biomass (-5.4%), starch concentration (-3.0%), starch yield (-10.9%), and protein yield (-6.2%). No significant effect was found for grain number and protein concentration. There was a significant relationship between the effect of filtration on grain yield and the difference in O3 concentration between NF and CF treatments. The average yield loss per ppb O3 removed was 0.38% and did not systematically vary with year of experiment (ranging from 1982 to 2010) or with the average O3 level in the experiments. Although there are many differences among the field experiments included in this meta-analysis (e.g. genotype, degree of O3 pollution of the site and year, nutrient and soil condition, filtration efficiency), our study clearly shows that there is a consistent and significant effect of present ambient O3 exposure on a range of important response variables in wheat, the most strongly affected being starch yield.