Wheat yield responses to stomatal uptake of ozone: peak vs rising background ozone conditions

Recent decades have seen a changing temporal profile of ground-level ozone (O3) in Europe. While peaks in O3 concentrations during summer months have been declining in amplitude, the background concentration has gradually increased as a result of the hemispheric transport of O3 precursors from other world regions. Ground-level O3 is known to adversely affect O3-sensitive vegetation, including reducing the yield of O3-sensitive crops such as common wheat (Triticum aestivum L.). The reduction in wheat yield has been shown to be linearly related to the phytotoxic O3 dose above a flux threshold of Y (PODY) accumulated over a specific period. In the current study, we tested whether the flux-effect relationships for wheat yield and 1,000-grain weight were affected by the temporal profile of O3 exposure. A modern wheat cultivar (Skyfall) was exposed to eight different realistic O3 profiles repeated weekly: four profiles with increasing background O3 concentrations (ca. 30–60 ppb) including small peaks and four profiles with increasing O3 peak concentrations (ca. 35–110 ppb). Both wheat yield and 1,000-grain weight declined linearly with increasing PODY. The slope of the flux-effect relationships was not affected significantly by the profile of O3 exposure. Hence, flux-effect relationships developed for wheat based on exposure to enhanced peak O3 concentrations are also valid for the changing European O3 profile with higher background and lower peak concentrations. The current study also shows that the modern wheat cultivar Skyfall is more sensitive to O3 than European wheat varieties tested for O3 sensitivity in the 1980s and 1990s.