Abstract: By the observation with electron and confocal laser scanning microscopy and the determination of physiological and biochemical reactions, the toxic effects of Hg²⁺, Cd²⁺ and Cu²⁺ on the cell membrane system of Cabomba caroliniana A. Gray were investigated. The results showed that under the actions of the three heavy metal ions, the contents of reactive oxygen species（ROS）and malondialdehyde (MDA) in C. caroliniana leaf cells increased, activities of protective enzymes were in disorder, and lipid peroxidation happened. The cell membrane was damaged, membrane permeability increased, and plasmolysis occurred. Meanwhile, the chloroplast swelled or even disintegrated. The excitement of photosynthetic pigments on thylakoids membrane by light was inhibited, and the auto-fluoresent intensity was decreased. The cristae of mitochondria swelled and decreased, mitochondria membrane was damaged, and nuclear membrane was broken. The effects of Hg²⁺, Cd²⁺ and Cu²⁺ on the cell membrane system of C. caroliniana showed a definite dose-effect correlation, and the stability of membrane system played a key role in the resistance of C. caroliniana to the toxic effects of heavy metals. C. caroliniana was sensitive to Hg²⁺, and the lethal concentration of Hg²⁺ was ranged from 0.3 to 0.5 mg·L^-1. C. caroliniana had relatively higher endurance to Cd²⁺ and Cu²⁺, and could be used as the resistant plant for biological control.

Key words: Lyusi fishing ground, trophic level, stable carbon and nitrogen isotope, coastal water