Abstract: The study with water culture showed that when treated with 0.056 mg Cu·L^-1,the chlorophyll a,b and (a+b) contents in Spirodela polyrrhiza and Lemna minor were increased by 11%,46% and 22%,and 8%,15% and 11%,while under 0.15～5.6 mg Cu·L^-1,the contents were decreased by 63%,62% and 63%,and 46%,45% and 45%,respectively,compared with no copper added.The malondialdehyde (MDA) content in S.polyrrhiza was 2.75 times higher than that in L.minor averagely.The superoxide dismutase (SOD),catalase (CAT) and peroxidase (POD) activities in both S.polyrrhiza and L.minor all increased first,but decreased then with increasing copper concentration.For S.polyrrhiza,the activities of test enzymes were the highest at 0.18 mg Cu·L^-1,but for L.minor,only when the Cu concentrations were up to 0.56,1.0 and 1.0 mg·L^-1,the activities of SOD,CAT and POD got to their peak values,respectively.It was concluded that higher concentrations of copper caused more damage to S.polyrrhiza than to L.minor,and the antioxidase system of the former was much more sensitive to the copper stress than that of the latter.

Key words: Swamp wetland, Vegetable organs, N content dynamics