Abstract: In this paper, Hydrilla verticillata was cultured in the hoagland solution containing 5 mg·L^-1 Cd²⁺ and different concentration ascorbic acid (AsA) to investigate the protective action of AsA to aquatic plant suffered from heavy metal′s stress. The O₂^-generation rate, H₂O₂ content, antioxidants (AsA and GSH) contents, and antioxidant enzymes (SOD, POD, CAT and APX) activities were analyzed. The results showed that compared with single Cd²⁺ treatment, AsA addition lessened the reactive oxygen species (O₂^- and H₂O₂) generation rates, endogenous AsA content, and antioxidant enzyme activities. It was concluded that exogenous AsA could relieve the Cd²⁺ poison to H. verticillata, and its optimum concentration was 60 mg·L^-1.

Key words: Brown-red soil of south Hubei Province, Agroecosystem, Boron balance