New Insights into Leaf Physiological Responses to Ozone for Use in Crop Modelling

Estimating food production under future air pollution and climate conditions in scenario analysis depends on accurately modelling ozone (O(3)) effects on yield. This study tests several assumptions that form part of published approaches for modelling O(3) effects on photosynthesis and leaf duration against experimental data. In 2015 and 2016, two wheat cultivars were exposed in eight hemispherical glasshouses to O(3) ranging from 22 to 57 ppb (24 h mean), with profiles ranging from raised background to high peak treatments. The stomatal O(3) flux (Phytotoxic Ozone Dose, POD) to leaves was simulated using a multiplicative stomatal conductance model. Leaf senescence occurred earlier as average POD increased according to a linear relationship, and the two cultivars showed very different senescence responses. Negative effects of O(3) on photosynthesis were only observed alongside O(3)-induced leaf senescence, suggesting that O(3) does not impair photosynthesis in un-senesced flag leaves at the realistic O(3) concentrations applied here. Accelerated senescence is therefore likely to be the dominant O(3) effect influencing yield in most agricultural environments. POD was better than 24 h mean concentration and AOT40 (accumulated O(3) exceeding 40 ppb, daylight hours) at predicting physiological response to O(3), and flux also accounted for the difference in exposure resulting from peak and high background treatments.