Nitrogen supply mitigates the effects of elevated [O_3] on photosynthesis and yield in wheat

Aims Our objective was to study the interactive influences of ozone (O3) and nitrogen (N) on photosynthesis and yield in winter wheat (Triticum aestivum). Methods The winter wheat was exposed to two levels of O3 (ambient and 1.5 ambient) and two levels of N sup- ply (210 and 250 kg·hm -2 ) under field conditions. Important findings O 3 exposure significantly reduced the net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of wheat leaves in the filling stage by 28.95%, 31.79 % and 23.17%, respectively. O3 exposure also significantly reduced the content of chlorophyll a (Chl a), chlorophyll b (Chl b), carotene (Car), total chlorophyll (Chl t) and soluble protein in the filling stage by 58.89%, 68.64%, 22.89%, 60.31% and 32.00%, respectively, while intercellular CO2 concentration (Ci) changed slightly. Biomass in the maturing stage and yield of the wheat were also reduced by elevated O3 by 12.23% and 12.63%, respectively. High N availability signifi- cantly increased Pn, Chl a, Chl b, soluble protein, biomass and yield of the wheat leaves by 25.66%, 83.05%, 121.57%, 30.33%, 14.94% and 10.67%, respectively, while Gs, Ci, Tr and Car were influenced slightly by high N, which indicated that the increase of Pn was mainly caused by the increment of Chl a, Chl b and soluble protein. The interactive effects of O3 and N on the concentrations of Pn, Chl a, Chl b and soluble protein were significant. These results suggest that sufficient N supply can modify the effects of elevated O3 on photosynthesis and yield in