Can Reduced Irrigation Mitigate Ozone Impacts on an Ozone-Sensitive African Wheat Variety?

Ground-level ozone (O₃) pollution is known to adversely affect the production of O₃-sensitive crops such as wheat. The magnitude of impact is dependent on the accumulated stomatal flux of O₃ into the leaves. In well-irrigated plants, the leaf pores (stomata) tend to be wide open, which stimulates the stomatal flux and therefore the adverse impact of O₃ on yield. To test whether reduced irrigation might mitigate O₃ impacts on flag leaf photosynthesis and yield parameters, we exposed an O₃-sensitive Kenyan wheat variety to peak concentrations of 30 and 80 ppb O₃ for four weeks in solardomes and applied three irrigation regimes (well-watered, frequent deficit, and infrequent deficit irrigation) during the flowering and grain filling stage. Reduced irrigation stimulated 1000-grain weight and harvest index by 33% and 13%, respectively (when O₃ treatments were pooled), which compensated for the O₃-induced reductions observed in well-watered plants. Whilst full irrigation accelerated the O₃-induced reduction in photosynthesis by a week, such an effect was not observed for the chlorophyll content index of the flag leaf. Further studies under field conditions are required to test whether reduced irrigation can be applied as a management tool to mitigate adverse impacts of O₃ on wheat yield.