Abstract: The tolerance of alien species Hyriopsis schlegeli (C), native species H. cumingii (S), and their reciprocal hybrids F₁ SC and CS to low dissolved oxygen, drying condition and heavy metal Hg was studied to evaluate the ecological risk of introducing alien species H. schlegeli. The results indicated that CS had the strongest tolerance to low dissolved oxygen, with its asphyxia point being 0.92 mg·L^-1, followed by C and SC, with their asphyxia point being 1.04 mg·L^-1 and 1.10 mg·L^-1, respectively, while S had the weakest tolerance to low dissolved oxygen, with its asphyxia point being 1.31 mg ·L^-1. In this aspect, S had significant differences (P<0.01) with the others. No significant difference was observed on the tolerance to drying condition between H. schlegeli and its reciprocal hybrids F₁, but there existed significant difference between H. cumingii and the others. The tolerance to heavy metal Hg was in the order of C＞CS ＞SC＞S, judging from the median-lethal concentration of Hg²⁺. It could be concluded that alien species H.schlegelii had a stronger tolerance than native species H. cumingii, and the inspection and precaution of H. schlegeli should be strengthened to avoid its threatening the survival of H. cumingii.

Key words: Aluminum-based coagulation, Ecotoxicology, Seed germination, Root elongation, Inhibitory rate