The development, calibration and application of the DO3SE-Crop model to assess ozone's effect on grain and protein yield in wheat

Wheat is a global staple crop, providing 40% and 47% of daily calories and protein. However, tropospheric ozone (O3) threatens wheat yields and quality. While several risk assessments have investigated O3’s impacts on wheat yields at varying geographical scales, the reduction in protein has not been included. The Indo-Gangetic Plains in India, a key wheat-growing region, face high and rising O3 levels. Given India’s existing food and nutrition security challenges, understanding O3’s threat to wheat yields and protein is essential to inform policy, mitigation and adaptation strategies. This thesis develops a framework for estimating O3 effects on wheat protein yields, concentration and quality, suitable for risk assessments, by developing a nitrogen (N) (and protein) module for the stomatal O3 deposition crop model, DO3SE-Crop. In paper 1, the module is developed and identifies the key plant process affecting wheat N under O3 as early senescence onset (simulated as being ~13 days earlier in the very high vs low O3 treatment). In paper 2, the module is extended for Indian wheat, and a framework is presented for using the model to calculate protein quality, through amino acids and metrics recommended by the Food and Agricultural Organisation. While the lysine and methionine concentrations were simulated well, the decrease in methionine concentrations under O3 exposure was underestimated by ~10 percentage points. The underestimation was greater for lysine. In the final paper, different risk assessment methods, input data and cultivar O3 sensitivity are tested and compared with the newly developed model to understand risk assessment uncertainties. Risk assessment method was the largest source of relative yield (RY) variability (0<RY<1), followed by input data (0<RY<0.8). Cultivar O3 sensitivity contributed very little to variations in RY estimates (magnitude of 12 percentage points) but had a greater effect on protein (magnitude of ~40 percentage points).