Differential Sensitivity of Growth and Net Photosynthetic Rates in Five Tree Species Seedlings under Simulated Acid Rain Stress

Abstract

This study investigated the effect of simulated acid rain (SAR) (heavy: pH 2.5; moderate: pH 4.0; and control: pH 5.6) stress on the growth and net photosynthetic rate (Pn) of five tree species, namely Castanopsis sclerophylla, Cinnamomum camphora, Manglietia fordiana, Pinus massoniana, and Elaeocarpus glabripetalus. Results showed variable responses to SAR with different pH values depending on the type of plants. P. massoniana seedlings exhibited significant growth reduction in response to all of the SAR treatments. The net photosynthetic rate of P. massoniana treated by SAR decreased by 20 and 34% under pH 4 and 2.5, suggesting that P. massoniana was susceptible when exposed to acid rain. These results indicate that P. massoniana was the highest sensitivity inhibitory type to SAR and should be protected. However, the growth, chlorophyll content, and Pn of three species (C. sclerophylla, C. camphora, M. fordiana) revealed the following result: moderate acid rain > control > heavy acid rain, suggesting that moderate acid rain promoted photosynthesis and growth to some extent. Among the five species, E. glabripetalus exhibited the highest extent of tolerance to acid rain. The sensitivity of growth and Pn of E. glabripetalus was significantly higher than that of the control, indicating that SAR promoted rather than inhibited its seedling, E. glabripetalus belonging to the promotional type. The stress tolerance of five species of trees to SAR was observed in the following order: E. glabripetalus > C. sclerophylla, C. camphora, M. fordiana > P. massoniana. But exposure to SAR at PH 2.5 to 5.6 did not affect the final mortality of five tree species.