Abstract: Willow is one of the suitable species for phytoremediation on heavy metal polluted soil in wetlands. In this study, we investigated the phenotypic and physiological responses of seedlings of Salix integra Yizhibi under flooding and Cu stress during different treatment periods. The willow plants were cultivated in Cupolluted soils under the treatments of flooding (F, with water level of 10 cm above the soil surface) and nonflooded (NF, normal soil moisture). The Cu treatments were set as 0, 50, 150 and 450 mg·kg^-1 of Cu spiked with CuSO₄·5H₂O. Under flooding condition, white lenticels and adventitious root emerged from stem base to adapt to the flooding environment, while only a few adventitious roots were found at high Cu concentration (450 mg·kg^-1). Photosynthetic pigments and photosynthetic capacity substantially decreased as the flooding treatment prolonged. Photosynthetic rate (P_n)  was reduced by 9.19%-44.48% with the increasing Cu concentration. Leaf superoxide dismutase (SOD) activity was elevated with the prolonged flooding period and the increased Cu levels. Peroxidase (POD) and catalase (CAT) activities were slightly decreased by soil flooding, which still maintained a certain activity toadapt to normal growth under flooding condition. With the prolonged flooding treatment and the elevated Cu level, the Malonaldehyde (MDA)  content in leaves increased. MDA content in leaves significantly increased by 8.52%-70.44% when being flooded for 60 d. Under flooding condition, the concentrations of superoxide anion radical (O₂^-_·) and soluble protein showed the similardecreasing tendency.Salix integra showed strong growth, photosynthetic and physiological adaptation to Cu polluted soil for a long-term flooded period (except for high Cu concentration), indicating that willow could adapt to Cu polluted wetland.

Key words: Cluster analysis, Principal component analysis, River water quality, Xiangxi River