The grain quality of spring wheat (Triticum aestivum L.) in relation to elevated ozone uptake and carbon dioxide exposure

Ozone (O₃) and carbon dioxide (CO₂) effects on the quality of spring wheat (Triticum aestivum L.) were evaluated. The dataset originated from 13 European open-top chamber experiments, including three countries, 10 years and four cultivars. The O₃ exposure significantly reduced the protein yield, even though the grain protein concentration (GPC) was increased and tended to increase the Zéleny value and the Hagberg falling number. These variables reached values representing enhanced grain maturity after elevated O₃ exposure, possibly explained by O₃ induced early senescence. The CO₂ elevation was demonstrated to increase the protein yield but reduce the GPC and the Zéleny value. Both O₃ and CO₂ were demonstrated to affect wheat grain yield (GY) but by different means; O₃ reduced GY (P <0.001) mainly by limiting the 1000-grain weight, while CO₂ enhanced GY (P <0.01) mainly by increasing the number of grains produced per unit ground area. Two earlier used O₃ indices, the accumulated stomatal uptake of O₃ above a flux threshold of 6nmolm⁻² s⁻¹ (AFst6), and the accumulated O₃ dose above a concentration threshold of 40nmolmol⁻¹ (AOT40), were employed in parallel in the derivation of dose-response relationships with all investigated variables (GY, number of grains per unit area, 1000-grain weight, protein yield, GPC, Zéleny value, wet gluten, dry gluten, starch concentration, Hagberg falling number, specific weight and water quotient). The uptake-based index (AFst6) tended to better explain variation in the response variables and yielded dose-response regressions of a higher statistical quality than did the external-dose index (AOT40). Based on an independent subset of the present data, the validities of (1) a negative linear relationship between GPC and GY and (2) a positive but decelerating relationship between protein yield and GY including both O₃ and CO₂ treatments were tested and confirmed.