Objective To investigate the mechanism of lead and cadmium tolerance and detoxification of Hemerocallis and to provide a theoretical basis for the phytoremediation in lead and cadmium contaminated soils.

Method A pot soil experiment was designed to study the accumulation characteristics of two types of Hemerocallis after different treatrnent time of Pb and Cd. The differential antrifugation and chemical reagent extraction technique was carried out to analyze the distribution and chemical form of Pb and Cd in these plants.

Result and conclusion The absorption characteristics of two types of Hemerocallis were that the contents of Pb and Cd in the underground part were more than those in the aboveground part. With the treatment time increasing, a peak value emerged in both of plants in the process of absorption, but peak times were different. The transfer coefficients of Pb and Cd both reduced. Most of Pb was found in the vacuolus and cellular soluble parts, then in the cell wall and its residue and less Pb in the cell membranes and organelles. The chemical form Pb distribution in Hemerocallis fulva was: Pb_HCl > Pb_NaCl > Pb_W > Pb_E > Pb_HAc > Pb_r, while Hemerocallis×hybrida'stella deoro' was: Pb_HCl > Pb_HAc > Pb_NaCl > Pb_W > Pb_E > Pb_r. The chemical form Cd distribution in two plants was as follows: Cd_E > Cd_NaCl > Cd_W > Cd_HAc > Cd_HCl > Cd_r. The Cd distribution forms of two types of Hemerocallis are mainly inorganic salts, amino acids and other soluble salts. The cell wall plays an important role in cadmium tolerance and detoxification. The Pb distribution form is mainly metal phosphate. The vacuolus is the most important part for Pb tolerance and detoxification.