Development of the DO ₃ SE-Crop model to assess ozone effects on crop phenology, biomass, and yield

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 around the world. Here we extend the DO3SE model (designed to estimate total and stomatal O3 deposition for risk assessment) to incorporate a coupled Anet–gsto model to estimate O3 uptake; an O3 damage module (that impacts instantaneous Anet 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 parameterised using O3 fumigation data from Xiaoji, China, for the year 2008 and for an O3-tolerant and sensitive cultivar. The calibrated model was tested on data for different years (2007 and 2009) and for two additional cultivars and was found to simulate key physiological variables, crop development, and yield with a good level of accuracy. The DO3SE-Crop model simulated the phenological stages of crop development under ambient and elevated O3 treatments for the test datasets with an R2 of 0.95 and an RMSE of 2.5 d. The DO3SE-Crop model was also able to simulate O3-induced yield losses of ∼11 %–19 % compared to observed yield losses of 12 %–34 %, with an R2 of 0.68 (n=20) and an RMSE of 76 g m−2. Additionally, our results indicate that the variance in yield reduction is primarily attributed to the premature decrease in carbon assimilation to the grains caused by accelerated leaf senescence, which is brought forward by 3–5 d under elevated O3 treatments.