| Pb and Cd accumulation and transfer in different organs of five two-year species of koelreuteria paniculata, Forsythia suspense, Berberisthunbergiicv atropurpurea, Jasminum nudiflorum, Cornus alba under heavy metal Pb and Cd stess were studied through water culture experiments. The transfer ability of the koelreuteria paniculata, Forsythia suspense, Berberisthunbergiicv atropurpurea, Jasminum nudiflorum, Cornus alba species for Pb and Cd were tested and analyzed to make sure whether they are the perfect plants in renovating heavy metal. Thus, scientific references were provided for selecting proper species in urban areas to renovating heavy metals in soil.Results showed that for koelreuteria paniculata, Forsythia suspense, Berberisthunbergiicv atropurpurea, Jasminum nudiflorum, Cornus alba species the absorption ability trend of heavy metals was root＞stem＞leaf. Their content of heavy metals Pb and Cd were added but transfer factor of Pb and Cd were reduced with the increase of Pb and Cd concentration. Pb content trend was koelreuteria paniculata＞Forsythia suspense＞Berberisthunbergiicv atropurpurea＞Jasminum nudiflorum＞Cornus alba, while the Cd content trend was Forsythia suspense＞koelreuteria paniculata＞Berberisthunbergiicv atropurpurea＞Jasminum nudiflorum＞Cornus alba. Transfer factor trend of Pb was koelreuteria paniculata＞Forsythia suspense＞Berberisthunbergiicv atropurpurea＞Jasminum nudiflorum＞Cornus alba, while transfer factor trend of Cd was Forsythia suspense＞koelreuteria paniculata＞Berberisthunbergiicv atropurpurea＞Jasminum nudiflorum＞Cornus alba. Critical values of Pb, Cd in koelreuteria paniculata, Forsythia suspense, Berberisthunbergiicv atropurpurea, Jasminum nudiflorum and Cornus alba were 500 mg·kg-1 and 100 mg·kg-1 respectively.Effects of single and combined Pb and Cd stress on the growth, Physiological biochemical characteristic and photosynthesis of Salix babylonica in different time were tested with concentration gradients of Pb and Cd added to soil. Pb and Cd resistance, accumulation and distribution of Salix babylonica were analyzed, and critical values of Pb and Cd in soil for planting Salix babylonica were defined. The results were as follows:1. Height growth, root growth and biomass of Salix babylonica were all rejected under single and combined Pb and Cd stress, and the inhib function was raised with increase of concentration. Content trend of heavy metals in different organs of Salix babylonica was root＞stem＞leaf, and the content raised with increase of concentration. The effects of Pb and Cd combined stress were more significant than those of Pb and Cd single stress. Compared with controls, the content of Pb and Cd with high concentration reached a significant level. The allocation coefficient trend of Pb and Cd in Salix babylonica was root＞stem＞leaf. The transfer factor was less than 1, indicating that Salix babylonica was not over-accumulation plant. The critical value of Pb and Cd for Salix babylonica were 500 mg·kg-1 and 30 mg·kg-1 respectively.2. Membrane permeability and content of MDA of Salix babylonica leaf were added with increase of Pb and Cd concentration. When the concentration of Pb and Cd were 750 mg·kg-1 and 60 mg·kg-1 respectively, significant differences from the controls appeared. Activity of SOD, POD, CAT, APX and content of GSH, soluble protein, soluble sugar raised at first, but then reduced with the increase of Pb and Cd concentration and time. Yet free praline content increased all the time with the increase of Pb and Cd concentration. The trends of protective enzyme activity and permeate content were different in different months, but in general the effects of Pb and Cd combined stress were stronger than those of Pb and Cd single stress.3. Under Pb stress, the production rate of superoxide anion radical, Membrane permeability of Salix babylonica were closely related to MDA, and showed significant positive correlation. Membrane permeability index and POD, APX were negative correlation, but it was positively correlated with SOD, POD, APX and soluble sugar. Membrane permeability index and SOD, POD, APX and soluble protein were negative correlation, but it was positively correlated with CAT, soluble sugar and free praline. Under combined Pb and Cd stress, membrane permeability index and SOD, POD, CAT, APX and soluble protein were negative correlation. Protective enzyme and GSH, free praline, soluble protein were negative correlation, but it was positively correlated with soluble sugar.4. Under Pb and Cd single stress and combined stress, Pn, Tr, Gs in Salix babylonica leaf increased at first and decreased later with the increase of Pb and Cd concentration, but Ci showed opposite trend. Value of Pn, Tr, Gs were highest in 11 at morning in a day, and decreased with time extend. The variation of Ci concentration showed a trend of "V" form. Variation trends of Pn, Tr, Gs and Ci in Salix babylonica leaf were different in different seasons.At the same time, the absorption, distribution and accumulation ability for Pb, Cd, Cu, Zn, Cr, Ni of Populus tomentosa, which were of 3 aged,5aged and 10 aged and along the polluted river road area in Xijiao of Baoding city, were studied in order to identify the ability of Populus tomentosa in accumulating and transfering heavy metals. The results were as follows:5. The trend of heavy metal absorption ability of Populus tomentosa was 3 years＞5 years＞10 years, and the trend of heavy metal content was Zn＞Cu＞Cd＞Cr＞Pb＞Ni. Heavy metals content of Populus tomentosa were high in leaf, root and bark, but low in branch and stem. Transfer ability for Pb, Cr, Zn and Ni were reduced with the increase of age. Transfer factor of Populus tomentosa was greater than 1, indicating that Populus tomentosa was better in transferring Pb, Zn, Cu, Cr, Cd and Ni. Concentration coefficient of Populus tomentosa for Pb, Cu, Zn, Cr and Ni were decreased with the increase of its age.
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