Abstract:The gas exchange,chlorophyll fluorescence parameter,Chlorophyll (chl) contents and chloroplast ultrastructure of two Miscanthus floridulus populations, one population from Boluo an uncontaminated site,and another population from Dabaoshan a mine site, were studied under pot-cultivation experiments treated with heavy metal Cd in green house. The results showed that, (1)Under Cd stresses, the net photosynthetic rate(Pn), transpiration rate(Tr), stomatal conductance and chlorophyll content decreased at different extents, and chloroplast ultrastructure was damaged in the leaves of both populations.Compared to the non-mine population,the net photosynthetic rate of the mine population decreased more slowly,and chloroplast shape and grana structure were less affected. (2)Stomatal restriction was the main factor for the Pn′s decrease in the leaves of the non-mine population under light Cd stress, while the non-stomatal restriction was the main factor for Pn′s decrease in the leaves of the non-mine population under middle and high Cd stresses. (3) Measurement of fluorescence of PSⅡReaction Center indicated Fv/Fm, Fv′/Fm′ and Fv/Fo to decrease in the both populations under Cd stress. However, Fv/Fm and Fv/Fo showed a smaller decrease, but the capability to utilize light and the potential to activate PSⅡ of the mine population remained higher than that of the non-mine population.Quenching(qP) of chlorophyll fluorescence decreased and Non-photochemical Quenching(NPQ) of chlorophyll fluorescence increased for the both populations under Cd stress. Generally, qP decreased less and NPQ increased more for the mine population than that for the non-mine population. Electronic transfer rate (ETR) and PSⅡactual fluorescence efficiency (ΦPSⅡ) of the mine population changed slightly under Cd stress.These results indicated that when under Cd stress, the electron transport activity and photosynthetic apparatus were damaged less in the mine population with high resistance than in the non-mine population with low resistance. Therefore,the Miscanthus floridulus populations from Dabaoshan could be a pioneer species for restoration and rehabilitation of vegetation in a mining area.