Developing the DO3SE-crop model for Xiaoji, China

Abstract. A substantial body of empirical evidence exists to suggest that elevated O₃ levels are causing significant impacts on wheat yields at sites representative of highly productive arable regions of China. Here, we extend the DO₃SE model (designed to estimate total- and stomatal- O₃ deposition for risk assessment) to incorporate a coupled A_net-g_sto model to estimate O₃ uptake, an O₃ damage module (that impacts instantaneous A_net and the timing and rate of senescence), and a crop phenology, carbon allocation and growth model based on the JULES-Crop model. The model structure allows scaling from the leaf to the canopy to allow for multiple leaf populations and canopy layers. The DO₃SE-crop model is calibrated and parametrised using O₃ fumigation data from Xiaoji, China for the year 2008 and for an O₃ tolerant and sensitive cultivar. The calibrated model can simulate key physiological variables, crop development, and yield with a good level of accuracy compared to experimental observations. DO₃SE-crop accurately depicted the difference in yield reductions under ambient and elevated O₃ treatments for wheat cultivars Y16 (tolerant) and Y2 (sensitive) with regressions of modelled and observed absolute yields resulting in an R² of 0.99 and an RMSE of 9.27 g/m². Further, when evaluated for 2007 and 2009 for all cultivars, the DO₃SE-crop model simulated O3-induced yield losses of 4–25 % compared to observed yield losses of 12–34 %, with an R² of 0.73 and an RMSE of 58.41 g/m². Additionally, our results indicate that the variance in yield reduction is primarily attributed to the premature decrease in carbon assimilation to the grains under elevated O₃ exposure. This is linked to accelerated leaf senescence, which brings leaf senescence forward by 7–9 days under elevated O₃ treatments.