Abstract
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.
Highlights
Tropospheric ozone (O3 ) is a secondary pollutant formed in the atmosphere by chemical reactions between the O3 precursors carbon monoxide, nitrogen oxides, methane, and non-methane volatile organic compounds in the presence of solar radiation [1,2]
The first two weeks of the irrigation period were marked by unusually warm weather, some watering was required on the second day after full watering in the infrequent deficit (ID) treatment to prevent drought stress occurring
This study demonstrates for the first time that deficit irrigation potentially be applied as a management tool to mitigate adverse impacts of O3 on crop yield
Summary
Tropospheric ozone (O3 ) is a secondary pollutant formed in the atmosphere by chemical reactions between the O3 precursors carbon monoxide, nitrogen oxides, methane, and non-methane volatile organic compounds in the presence of solar radiation [1,2]. Concentrations over much of the Earth’s land surface have more than doubled due to anthropogenic emissions from vehicles, industry, and agriculture [1,2,3,4,5]. United States and parts of Europe due to precursor emission controls. O3 concentrations have been increasing rapidly in developing regions such as south and east Asia [6,7] and are predicted to continue to increase in the coming decades unless more stringent air pollution and climate change controls are implemented in those regions [8]. Surface O3 concentrations can reach peaks up to 70 ppb in Rwanda [9] and 80 ppb in South Africa [10]
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