Abstract: Complex effects of the different intensity of acid rain and cadmium(Cd)on chlorophyll content,Hill reaction rate,Mg2+-ATPase activity,fluorescence parameters and chloroplast ultrastructure in soybean seedling were investigated by biochemical analysis method,chlorophyll fluorescence system and transmission electron microscopy.The results indicated that compared with the control,in the single action of acid rain and Cd,the tendency of change in the test indexes was shown in the different way,which was the decrease in the chlorophyll content,Hill reaction rate and Mg2+-ATPase activity,the decrease and then increase in the initial fluorescence,and the increase and then decrease in the maximal photochemical efficiency(F) and maximal quantum yield.In the complex action of acid rain and Cd,the additive and synergistic effect of the single action mentioned above were observed in the change in the chlorophyll content and the Hill reaction rate(Mg2+-ATPase activity),respectively.Meanwhile,the antagonistic(synergistic) effect of the single action of acid rain and the low(high) concentration of Cd was observed in the change in the fluorescence parameters.Moreover,in the complex action of acid rain and Cd,the chloroplast ultrastructure in soybean seedling was damaged.It was further obtained from the change in the test indexes that the damage of chloroplast ultrastructure was one of the reasons why the chlorophyll content,light reaction and then photosynthesis of soybean seedling in the complex treatment with acid rain and Cd were inhibited.

Key words: Acid rain, Acid rain, Cadmium, Soybean seedling, Photosynthesis, Complex toxic effects