Abstract: We examined the effect of simulated acid rain (pH 2.5, 4.5, 5.6) on gas exchanges of 3 compositae invasive plants (Wedelia trilobata, Mikania micrantha and Chromolaena odoratum). Leaves of the 3 invasive plants showed injury under severe acid rain stress (pH 2.5). The order of the injury degree was C. odoratum > M. micrantha > W. trilobata. The 3 invasive plants showed different photosynthetic responses to simulated acid rain stress. The chlorophyll (Chl) content of C. odoratum and M. micrantha was reduced with decreasing pH, and thus the net photosynthetic rate (P_n) was inhibited, with no difference for W. trilobata. Instead, its P_n increased, although not significantly. Under acid rain treatment, membrane permeability, malondialdehyde content and superoxide dismutase (SOD) and peroxidase activity increased for all plants to varying degrees, which showed some resistance to acid rain. W. trilobata showed the greatest increase in SOD activity under pH 2.5, which suggests its fast response to acid rain stress. W. trilobata had stronger adaptability and tolerance to acid rain than the other 2 invasive plants and could be further investigated in light of increasing acid rain pollution.

Key words: adaptability, invasive plant, gas exchanges, simulated acid rain, tolerance