| The problem of heavy metal pollution in cities had not been underestimated,and it had become an important issue that threatens the living environment and human health,attracting people's attention.In recent years,the use of plants to absorb heavy metals had become a research hotspot,but the current research objects were mostly concentrated on herbaceous and seedling woody plants.There were relatively few studies on adult trees growing in the field,and in the existing research,they were also in a single plot or Most of the measurements in a single time.In view of the above problems,this study used 40 kinds of adult garden tree leaves and annual branches in 6 different garden green spaces in Beijing as test materials,and carried out a two-year measurement.On this basis,the ability of garden trees to absorb heavy metals was evaluated.The evaluation system is discussed in order to screen out the tree species with strong ability to absorb heavy metals more accurately,quickly and easily,and provide a basis for the selection of tree species for ecological construction in Beijing.The main results are as follows:(1)Among the 40 garden trees studied,in the total number of tree leaves and annual branches,Picea meyeri,Chionanthus retusus,Chaenomeles speciosa,Lonicera maackii,Lagerstroemia indica,Pinus tabuliformis,Sabina chinensis had strong Cd absorption capacity,ranging from 0.33 to 0.58 mg/kg,while Cornus officinalis,Rhodotypos scandens,Cercis chinensis,Pterocarya stenoptera,Sophora japonica and Fraxinus pennsylvanica were weak,ranging from 0.10 to 0.17 mg/kg.Picea meyeri,Lonicera maackii,Chaenomeles speciosa,Sabina chinensis,Cedrus deodara,Ginkgo biloba,Pinus tabuliformis and Sabina chinensis had strong absorption capacity for Pb,ranging from 15.10 to 40.64 mg/kg,while Eucommia ulmoides,Cornus officinalis,Rhodotypos scandens,Amygdalus davidiana,Cercis chinensis,Forsythia suspensa and Fraxinus pennsylvanica were weak,content was 7.69?9.97 mg/kg.Picea meyeri,Lonicera maackii,Cedrus deodara,Hibiscus syriacus and Syringa reticulata var.amurensis had strong absorption capacity for Cu,and the content was between 26.50 and 35.51 mg/kg,while Pinus armandii,Cornus officinalis,Chionanthus retusus,Weigela florida,Amygdalus persica var.persica f.duplex and Sorbaria sorbifolia were weak,ranging from 17.28 to 19.18 mg/kg.(2)Among the 40 kinds of garden trees and annual branches,Picea meyeri,Lonicera maackii,Cedrus deodara,Sabina chinensis,Ginkgo biloba and Chaenomeles speciosa had stronger absorption capacity for Cd,Pb and Cu.Pterocarya stenoptera,Cornus officinalis,Rhodotypos scandens,Amygdalus persica var.persica f.duplex and Sorbaria sorbifolia were weaker.(3)The content of heavy metals in tree leaves and annual branches varied with tree species and heavy metals.The heavy metal absorption capacity of leaves and annual branches were different.The Cd content of 40 tree leaves absorbed were between 0.03?0.14 mg/kg,and the Pb content were absorbed between 3.19 and 9.04 mg/kg,the absorbed Cu content were between 7.48 and 18.87 mg/kg.The Cd content of the branches were between 0.06 and 0.51 mg/kg,and the absorbed Pb content were between 2.82 and 36.67 mg/kg.The Cu content were between 6.09 and 30.85 mg/kg,and the leaf and annual branches were inconsistent with the overall order.This study showed that only 40 branches of trees had a positive correlation with the Cd content of leaves,and the correlation coefficient was 0.20(p<0.05),while Pb and Cu were not related.(4)Ten annual seedlings of 40 species of trees were selected for pot cultivation and treated with similar concentrations of heavy metals in adult soil.The results showed that there was no significant correlation between adult trees and corresponding annual seedlings in the order of their ability to accumulate three heavy metals.(5)The results of determination of heavy metal absorption in roots,stems and leaves of 10 seedlings under different heavy metal concentrations showed that the absorption capacity of different organs were different.The Cd content of leaves was between 0.05-0.89 mg/kg,the Pb content was between 3.37 and 153.53 mg/kg,and the Cu content was between 5.10 and 77.19 mg/kg.The Cd content of the branches was between 0.04 and 1.11 mg/kg,the Pb content was between 1.49 and 402.98 mg/kg,and the Cu content was between 9.63 and 383.10 mg/kg.The Cd content of root was between 0.22 and 1.16 mg/kg,the Pb content was between 24.58 and 423.26 mg/kg,and the Cu content was between 32.08 and 419.84 mg/kg.Root was the main absorption organ of heavy metals.There were differences in the heavy metal transport coefficients of different seedlings.And the transport coefficient was affected by the concentration of heavy metal treatment.Among the 10 seedlings,Weigela florida,Pinus bungeana and Syringa reticulata var.amurensis had the strongest transport ability to Cd,Pb and Cu,respectively,Sorbaria sorbifolia,Ginkgo biloba and Sabina vulgaris were the weakest.(6)The relationship between the absorption capacity of heavy metal elements in adult tree leaves and the surface characteristics of leaves was related to the types of heavy metals.The stomatal density,stomatal length and roughness of the leaves were beneficial to the absorption of Pb by plants,and there were no correlation between Cd and Cu.(7)There was no significant correlation between heavy metal content and total chlorophyll content,antioxidant enzyme activity and MDA content in leaves and annual shoots of adult trees.Under the Pbl treatment,the Pb content and the total Pb content of the shoots were significantly correlated with the CAT activity,and the coefficients were 0.89 and 0.92,respectively(P<0.01).Under Cu? treatment,the Cu content and the total Cu content of the shoots were significantly correlated with the POD enzyme activities,and the coefficients were 0.77 and 0.75,respectively(P<0.01).Under Cul treatment,the Cu content and the total Cu content of the branches were significantly correlated with the total chlorophyll content,and the coefficients were 0.80 and 0.84,respectively(P<0.01).There were significant correlations between Cu content and plant height and root length change in 10 seedlings under Cu? treatment,and the correlation coefficients were 0.59 and 0.69,respectively(P<0.01).There was a significant correlation between Cu content,total Cu content and root length change under the treatment,and the correlation coefficients were 0.62 and 0.77,respectively.It suggested that by controlling the pot concentration,the relevant growth physiological indicators can be used to indicate its ability to absorb heavy metals.This study targeted 40 adult trees in garden green space within two years.The ability to absorb three heavy metals of Cd,Pb and Cu was evaluated,and the tree species with strong ability to absorb Cd,Pb and Cu were screened out.The evaluation system of the ability of garden trees to absorb heavy metals was discussed.It is concluded that the stomatal density,length and surface roughness of adult trees have a significant effect on the absorption of Pb by leaves.Through control experiments,the relevant growth physiological indicators of seedlings can be used to indicate their ability to absorb heavy metals. |
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