Abstract: We investigated the effects of exogenous melatonin on seed germination and some physiological indices of rice under As³⁺ and As⁵⁺ stress. The results showed that 50 and 100 μmol·L^-1 melatonin addition had positive effects on seed germination and growth of rice seedlings under As stress. Melatonin addition significantly increased the activities of antioxidant enzyme, such as CAT, POD, SOD, but decreased MDA content and the rate of O₂^-_· production. At As³⁺ concentration of 50 μmol·L^-1, compared with the control treatment, adding 100 μmol·L^-1 melatonin significantly increased the activities of CAT, POD and SOD of rice seedlings by 54.2%, 100.1% and 43.1%, respectively, decreased MDA content and O₂^-_· producing rate by 44.1% and 55.6%. At the same concentration of As⁵⁺, adding 100 μmol·L^-1 melatonin increased the activities of CAT, POD and SOD of rice seedlings by 62.1%, 49.6% and 47.3%, decreased MDA content and the rate of O₂^-_· production by 33.1% and 34.8%, respectively. The results suggested that the application of melatonin could alleviate lipid peroxidation damage in rice under As³⁺ and As⁵⁺ stress, and effectively alleviate the toxic effects of As³⁺ and As⁵⁺ on rice.

Key words: habitat, Zhangjiajie., Chinese giant salamander (Andrias davidianus), tourism disturbance, water quality