Extreme climate and ground level ozone (O3) air pollution stress are likely to co-occur and affect agro-ecosystems. This is due to elevated O3 episodes being more frequent under hot, dry sunny conditions as well as in agricultural regions (downwind of source O3 precursor pollutant emissions). A new international research project (CiXPAG) will collect experimental data for the development of modelling methods to assess the combined influence of heat, drought and O3 on photosynthesis, crop growth and yield (for both current and future projected climates). CiXPAG will focus on South Asia where high O3 concentrations and climate extremes are already threatening crop productivity in a food insecure region.
A coupled photosynthesis-stomatal conductance (Anet-gsto) model (DO3SE) will be used to estimate the exchange of CO2 (driven by supply and demand of CO2 for photosynthesis); water vapour and stomatal O3 uptake (both controlled by gsto). The DO3SE model has been developed to allow for O3 damage to Vcmax (the maximum carboxylation capacity of photosynthesis) based on methods similar to those developed by Martin et al. (2000) and Ewert et al. (1999). This model is capable of dynamically integrating the effects of climate extremes and O3 on crop growth and yield.
Results/Conclusions
Initial results show the capability of the Vcmax-O3 damage model to simulate changes in Vcmax under an elevated O3 exposure regime over the course of a growing season for soybean and wheat, both important South Asian crops. These results allow us to define an initial parameterization for the DO3SE model in terms of i. the starting Vcmax (which can be dependent upon species and soil fertility); and ii. the relationship between Vcmax and O3 both on an instantaneous (hourly stomatal O3 flux basis) as well as a seasonal (accumulated stomatal O3 flux) basis. These initial results will be further informed by observation and experimentation conducted in South Asia over the coming years. Ultimately, the model will be able to use fine scale meteorological and O3 data which will be available from the regional downscaling modelling planned in the CiXPAG project to inform policy through evaluating a number of emission storylines to identify those most likely to mitigate the effects of both O3 pollution and climate change. The work will also develop new O3 damage crop modelling methods that can be easily incorporated into existing photosynthesis-based crop modelling methods for application among the wider crop modelling community.