Photosynthesis and yield responses of ozone-polluted winter wheat to drought

Winter wheat (Triticum aestivum L. cv. Jingdong 8) was exposed to short-term high ozone treatment after anthesis and then was either well irrigated with soil water content (SWC) of 80-85 % (O3+W) or drought treated (SWC 35-40 %, O3+D). Short-term ozone exposure significantly decreased irradiance-saturated net photosynthetic rate (P N) of winter wheat. Under good SWC, P N of the O3-treated plant was similar to that of control on 2 d after O3-exposure (6 DAA), but decreased significantly after 13 DAA, indicating that O3 exposure accelerated leaf senescence. Meanwhile, green flag leaf area was reduced faster than that of control. As a result, grain yield of O3+W was significantly decreased. P N of O3+D was further notably decreased and green flag leaf area was reduced more than that in O3+W. Consequently, substantial yield loss of O3+D was observed compared to that of O3+W. Although P N was significantly positively correlated with stomatal conductance, it also had notable positive correlation with the maximum photochemical efficiency in the dark adapted leaves (Fv/Fm), electron transport rate (ETR), photochemical quenching (qP), as well as content of chlorophyll, suggesting that the depression of P N was mainly caused by non-stomatal limitation. Hence optimal soil water condition should be considered in order to reduce the yield loss caused by O3 pollution.