Effect of Simulated Acid Rain on the Physiological Activities and Chlorophyll Content of Leaves in Some Weeds and Crops

The effect of acid rain on the photosynthesis, respiration, stomatal conductance and chlorophyll content of leaves in 10 species including weeds and crops was investigated after spraying of simulated acid rain at pH 2.5-3.5, 6 or 8 times in 2 weeks. Plant species tested were divided into 3 groups according to their photosynthetic response to simulated acid rain. Photosynthetic activity in radish and kidney bean leaves decreased significantly after spraying of acid rain at a pH value below 3.0. In the case of Philadelphia fleabane and white clover leaves, the activity decreased after spraying of acid rain at pH 2.5, while it did not show any significant decrease in Polygonum lapathifolium, common lambsquarters, southern crabgrass, buckwheat, rice and tall fescue leaves. Respiration of the leaves increased in all the species after spraying of acid rain at pH 2.5. Stomatal conductance did not vary appreciably. Chlorophyll content of the leaves sprayed with acid rain decreased in the species tested except for southern crabgrass and tall fescue. A positive correlation was observed between the relative chlorophyll content, that is, the ratio of the chlorophyll a content of the treated leaves to that of the control leaves, and the relative photosynthetic rate which was calculated as mentioned above.