Impact of chronic elevated ozone exposure on photosynthetic traits and anti-oxidative defense responses of Leucaena leucocephala (Lam.) de wit tree under field conditions

Abstract In this study, the impact of long term exposure of elevated ozone (+20 ppb above ambient) on photosynthetic traits and anti-oxidative defense system of Leucaena leucocephala, a tree of great economic importance, was studied in a Free Air Ozone Concentration Enrichment (O3-FACE) facility at different time intervals (6, 12, 18, and 24 months). Results showed that net photosynthesis, photosynthetic pigments and lipid peroxidation were significantly reduced after 6, 12 and 24 months of exposure to elevated ozone (eO3) whereas stomatal conductance and transpiration rate were significantly decreased after 12 months of exposure to eO3. Antioxidant enzymatic activities (catalase, ascorbate peroxidase and glutathione reductase) were significantly increased after 12 months of exposure to eO3. Ascorbate was increased significantly after 6 and 12 months of exposure to eO3 while reduced glutathione content declined significantly after 6 and 24 months of exposure to eO3. The study showed that there were several negative long lasting physiological and biochemical responses in Leucaena. The results provide evidence that Leucaena exhibited greater sensitivity to O3 during initial exposure (up to 12 months) but showed moderate tolerance by the end of the 2nd year.