Photosynthesis and biochemical responses to elevated O3 in Plantago major and Sonchus oleraceus growing in a lowland habitat of northern China

A field experiment was carried out to compare the responses to ozone (O-3) in two common herbaceous plant species, Plantago major L. and Sonchus oleraceus L., by building open-top growth chambers in situ to simulate O-3 stress (+O-3, 85 +/- 5 ppb, 9 hr/ day for 30 days) in a lowland habitat in Inner Mongolia, Northern China. Responses to O-3 of gas exchange, chlorophyll a fluorescence, leaf pigment content, antioxidant capability, soluble protein content, membrane lipid peroxidation and dark respiration (R-d) were analyzed. Results showed that elevated O-3 exposure significantly reduced the light-saturated net photosynthesis (PNsat), stomatal conductance (g(s)) and transpiration rate (E) in both species. Although non-significant interactive effect between species and O-3 on PNsat was analyzed, the reduction in PNsat in S. oleraceus might be due primarily to the higher fraction of close PSII reaction centers and impaired activities of plant mesophyll cells as evidences by decreased maximum efficiency of PSII photochemistry after dark adapted state (F-v/ F-m) and unchanged intercellular CO2 concentration (C-i). Besides, biochemical analysis showed that S. oleraceus had lower antioxidant ability compared to P. major. As a result, S. oleraceus was damaged to the larger extent in terms of lipid peroxidation and visible O-3 injury, indicating that S. oleraceus was more sensitive to O-3 than P. major. Our results indicated that wild herbaceous plant species growing in a lowland habitat in sandy grassland were sensitive to O-3 stress and S. oleraceus can be considered as one of the bio-indicators for high O-3 concentration in semi-arid grassland of northern China. (C) 2016 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.