Developing and applying the DO3SE-crop model to assess ozone impacts on wheat

This PhD thesis investigates the impact of ground-level ozone (O3) pollution on wheat yields, focusing on areas in Europe, Asia, and particularly in China's productive arable regions. The research employs a mechanistic photosynthesis-stomatal conductance model (Anet gsto mech), DO3SE-crop, integrated with an O3 damage module to develop a new flux-based dose-response relationship for wheat crops in Europe, utilising a comprehensive dataset from European O3 fumigation experiments. The model's robustness (R2 = 0.82) is demonstrated, showing its effectiveness in simulating stomatal conductance (gsto) and photosynthesis (Anet) under high O3 concentrations and in predicting yield loss determinants such as the timing of senescence.
The thesis further extends the DO3SE-crop model, integrating it with the JULES-Crop. This integrated DO3SE-crop model successfully simulates crop development and yield, reflecting the differential impact of O3 on tolerant and sensitive wheat cultivars with high accuracy when evaluated for 2007, 2008, and 2009, with an R² of 0.73 and an RMSE of 58.41 g/m². Moreover, the thesis identifies the variance in yield reduction as primarily due to premature senescence and reduced carbon assimilation under elevated O3 levels, advancing leaf senescence by 7-9 days.
The DO3SE-Crop model, when calibrated for different Chinese agro-ecological zones (AEZs), exhibited an acceptable level of precision in simulating crop phenology, with estimated emergence and maturity dates aligning within a margin of 2.5 weeks of the observed data. The model also effectively simulates crop yield, with an accuracy range of ± 84 g/m2 as a mean yield by AEZ. However, the study also reveals the importance of accounting for regional climatic conditions in O3 damage assessment, highlighting the disproportionate impact of early O3 flux accumulation on certain AEZs. The study underscores the necessity of considering regional differences in AEZs for accurate parameterization of crop models, aiming to enhance their relevance and improve O3 damage assessment across varied international contexts.