| Roadside trees, the main tree species in road planting, are affected by Pb easily. So, in this paper, one-year old seedlings of Cinnamomum camphora (L.) Presl., Michelia maudiae Dunn, Koelreuteria paniculata Laxm and Liriodendron chinense(Hemsi.) Sargent were selected to study the physiological regularity and growth characteristics under the Pb stress in the soil, and to comprehensive evaluate the heavy metal resistance of these trees, for guiding the choice of tree species in urban planting. The main results were described as follows:(1)With the increase of Pb concentrations and the prolongation of the time of Pb stress, chlorophyll(Chl) contents all decreased, while relative conductivity rates, malonaldehyde(MDA) contents and free proline(Pro) contents all increased. The activity of peroxidase(POD) increased firstly, then decreased during early period under low concentrations of Pb stress, the decreased effect of Cinnamomum camphora (L.) Presl.was the most, three other species differently increased, but theirs difference was relative less. With the increase of Pb concentrations, the activity of superoxide dismutase (SOD)first increase then descend. Two antioxidant enzymes changed in the same trend. Pb at low concentration, promoted the increase of their content, while Pb at high concentration, made their content gradually decreased.(2)The harmfulness of seedling under the stress of different Pb concentrations were affected by Concentration main effect, tree species×concentration and tree species×concentrationxtime interactive effect. the physiological and biochemical indexes of four species under different concentrations of Pb stress changed differently, On basis of variance analysis and multiple-factor comparison, the results were described as follows: Researching relative conductivity, activity of POD, activity of SOD and free Pro contents of four species under different concentrations, it revealed initially that the ability of resistance to Pb stress of Cinnamomum camphora (L.) Presl is stronger, and that of Michelia maudiae Dunn is weaker, the Koelreuteria paniculata Laxm and Liriodendron chinense(Hemsi.) Sargent are situated between both. Researching Ch1 contents, MDA contents of four species under different concentrations, it showed that the resistance to Pb stress of Cinnamomum camphora (L.) Presl and Liriodendron chinense(Hemsi.) Sargent is stronger, and that of Michelia maudiae Dunn is weaker, Koelreuteria paniculata Laxm is situated between both.(3) From the appearances of seedling leaves, leaves appeared chlorosis symptom under the Pb stress,1600mg/L treatment was the most obvious, the symptoms with leaves turning yellow of Michelia maudiae Dunn and leafedge turning scorch, leaf abscission of Koelreuteria paniculata Laxm were the most obvious among four tree species.(4) The lower concentration of Pb can stimulate the growth of basal diameters, seedilng heights of most tree species, the effect on Cinnamomum camphora (L.) Presl was maximal. With the increase of Pb concentration, each indexes decreased, thereinto, the effect on Michelia maudiae Dunn was maximal. ithe growth of basal diameters, seedilng heights of four species under different concentrations of Pb stress showed different change trend, On basis of variance analysis and multiple-factor comparison, the results showed as follows:Researching the growth of seedilng heights of four species under different concentrations, it showed that the ability of resistance to Pb stress of Cinnamomum camphora (L.) Presl is stronger, and that of Michelia maudiae Dunn is weaker, the Koelreuteria paniculata Laxm and Liriodendron chinense(Hemsi.) Sargent are situated between both. Researching the growth of basal diameters of four species under different concentrations, it revealed that the ability of resistance to Pb stress of Cinnamomum camphora (L.) Presl and Liriodendron chinense(Hemsi.) Sargent is stronger, and Michelia maudiae Dunn is weaker, Koelreuteria paniculata Laxm is situated between both.(5)Selected these indexes, including relative conductivity, Ch1 contents, activity of POD, activity of SOD, MDA contents and free Pro contents, seedling height, basal diameters, comprehensive evaluation was conducted based on subordinate function method. The resistance of four tree species to Pb stress could be ordered as:Cinnamomum camphora (L.) Presl., Liriodendron chinense(Hemsi.) Sargent, Koelreuteria paniculata Laxm, Michelia maudiae Dunn. |
