Ozone-induced changes in physiological and biochemical traits in Elaeocarpus sylvestris and Michelia chapensis in South China

Abstract

The influences of elevated ozone (O3) concentrations on biomass, leaf gas exchange, fluorescence parameters, and leaf physiological and biochemical traits were examined in Elaeocarpus sylvestris and Michelia chapensis seedlings under four O3 conditions for a growing season in open-top chambers (OTCs). The four O3 concentrations were charcoal-filtered air (CF) (20 ppb), 1 × O3 air (40 ppb), 2 × O3 air (80 ppb), and 4 × O3 air (160 ppb), respectively. The significant decrease in the root/shoot (R/S) ratios of both species indicated that under O3 stress root biomass was more negatively affected than shoot biomass for both tree seedlings. Along with the loss of chlorophyll and carotenoid contents, decrease in the superoxide dismutase (SOD), and enhanced level of lipid peroxidant, the light-saturated net photosynthesis rate (Pnmax) of E. sylvestris, the effective quantum yield of PSII photochemistry (Y(II)) and the electron transport rate (ETR) of both species decreased, suggesting that impaired photosynthesis occurred. The negative effect of O3 on physiological and biochemical parameters was greater for M. chapensis than for E. sylvestris. As the O3 concentration increased, the leaf mass per area (LMA) of E. sylvestris decreased, while that of M. chapensis increased. Therefore, the increased SOD activity as a hormetic-compensatory response, the increases in LMA and longer vegetative period contributed to the good adaptability and high tolerance of M. chapensis.