Physiological and biochemical responses of two tree species in urban areas to different air pollution levels

We investigated the physiological and biochemical differences in Pterocarpus indicus and Erythrina orientalis grown in four sites at different pollution levels in the Philippines: Makati, Pasig and Quezon (high pollution levels; HP) located in Metro Manila, and La Mesa Watershed (a non-polluted area; NP). Among these four areas, HP sites had higher net photosynthetic rates (P_N) than NP sites, except for Makati. Among HP sites, Makati and Quezon had the lowest P_N for P. indicus and E. orientalis, respectively. Chlorophyll (Chl) contents were significantly lower in HP than in NP sites. Trees in Makati had the lowest Chl contents among HP sites, and P. indicus had higher Chl contents than did E. orientalis. In addition, the chloroplasts in HP trees had small starch grains with numerous dark, large plastoglobuli. Furthermore, antioxidant enzymes, indicative of the defense mechanism, showed a significantly higher activity in HP than in NP trees.