Abstract: A pot experiment was designed to study the changes of available Zn and Cd concentrations, characteristic of uptake, accumulation and removal effect by Sedum alfredii Hance under two treatments (T1: Zn 1200 mg·kg^-1 + Cd 20 mg·kg^-1; T2: Zn 300 mg·kg^-1 + Cd 2.0 mg·kg^-1) and at four pH levels (4.0, 5.5, 7.0 and 8.5). The results showed that available Zn and Cd concentrations in soil and the accumulated two metals by S. alfredii significantly increased with decreasing the pH. Under treatment T1, the highest plant dry weight was found at pH 5.5, but was not significantly different from that at the other three pH levels. The highest metal concentrations in shoot and root were at pH 4.0 for both T1 and T2. However, due to Al and Mn toxicity induced by low pH, plant had the lowest biomass at pH 4.0 for T2. The metal removal rate of S. alfredii was highest at pH 5.5, and lowest at pH 8.5 for both treatments. At pH 5.5, S. alfredii removed 16% and 1.33% of total Cd, Zn for T1, and 27%, 1.09% for T2, respectively. Overall, decreasing pH appropriately enhanced the removal efficiencies of Cd and Zn in soil by S. alfredii, and it may be a useful approach to enhance the phytoremediation of Cd and Zn contaminated soils by S. alfredii.

Key words: native plant, water level fluctuation, inter-specific competition, intra-specific competition, invasive plant