Study On The Enrichment Characteristics Of Different Forms Of Heavy Metals In Roadside Trees Of Sophora Japonica

At present,China is at a stage of rapid urbanization,and the population is constantly moving to cities.The people's need for a better life is growing.Correspondingly,the scale of the city is constantly expanding,the output of industrial and agricultural products is gradually increasing,and the urban road system is becoming increasingly perfect.The motor vehicle population has increased year by year.Urbanization also brings a series of environmental problems such as air pollution,water pollution and soil pollution.In recent years,Beijing has proposed the development goal of building a harmonious and livable capital.Other cities have also proposed the construction of forest cities and garden cities in order to improve the ecological environment.The role of urban forests in improving the urban ecological environment has been increasingly valued by the government and the people.Arbor species play an important role in purifying air and enriching soil heavy metals due to their advantages such as large biomass,long growth cycle,and obvious greening effect.In this study,the forest roads between the Landianchang North Road and the Jingmi diversion canal in Haidian District of Beijing were used as experimental plots.We extracted and measured the concentrations of heavy metals in different organs of Sophora japonica,soil and TSP,and analyzed the characteristics of the concentration of heavy metals in different organs of Sophora japonica,the distribution patterns of different heavy metals in Sophora japonica,and the accumulation capacity of heavy metals in different forms in Sophora japonica,plant enrichment characteristics of different forms of heavy metals in three greening patterns,and the correlation of concentrations of different forms of heavy metals among TSP,Sophora japonica and soil.The main conclusions are as follows:(1)The concentration of heavy metals in leaves showed a higher level during the spring growing season,and a lower concentration during summer growth,and the peak appeared in autumn,and the total concentration of heavy metals in abscission period decreased again.Pb and Cd elements gradually accumulated from spring to abscission period.There are significantdifferences in the forms of the different elements in the leaves,and this difference may vary with the season.The orientation of the leaves had a significant effect on the total concentration and the concentrations of various forms of heavy metals in the leaves.The overall performance was that the total concentration of heavy metals in the northward leaves was higher than that of the southward leaves,but the orientation of the leaves did not have a significant effect on the distribution of the forms of these elements.(2)The change trend of heavy metal concentration in the phloem of the tree with seasons generally showed a slight decrease in summer and then gradually increased.There are significant differences in the forms of the different elements in the phloem of the branches,and this difference changes with seasonal changes.The effect of orientation on the heavy metal concentration in the phloem of the tree was opposite to that of the leaves,showing that the total concentration of heavy metals in the phloem of the southern branches was significantly higher than that of the northward branches;the direction of the branches did not have a significant effect on the distribution of theforms of these elements in the phloem.(3)The concentration of heavy metals in the xylem of the annual ring generally shows that the longer the growth period,the lower the concentration of heavy metals.(4)There were significant differences among heavy metals concentration and heavy metal element enrichment forms in the organs of Sophora japonica,and the concentration of the 7heavy metal elements in bark was the highest.(5)The migration of heavy metal elements from tree root to trunk,trunk to branches and branches to leaves is mainly in acid-soluble form.The accumulation ability of heavy metal among in different organs was different.The bark and trunk are the main storage organs of heavy metal,and heavy metals exist in relatively stable forms in the two organs.(6)As a whole,the concentration of seven heavy metals in the Sophora japonica in Arbor-frutex-herb species community was higher than other two greening patterns.The enrichment amount per unit area of heavy metals was represented by the arrangement of arbor-frutex-herb species community>arbor-arbor-herb species community>arbor-frutex species community.The total amount of heavy metals per unit area in the three differentgreening patterns is arbor-arbor-herb species community>arbor-frutex-herb species community> arbor-frutex species community.(7)The concentration of heavy metals in TSP showed the characteristics of spring>autumn> summer.The concentrations of the seven heavy metals in the spring and autumn were n the the same in the order,and the concentration of Pb in summer was lower.On the whole,except for Cu and Zn,the concentrations of heavy metals in residue form in the TSP in spring,summer and autumn are relatively high.(8)The correlation of heavy metals in the same form between leaves and TSP,and phloem and TSP was different,and most of the elements in the leaves and phloem did not reach statistically significant levels with the same heavy metal elements in the TSP.(9)The correlations of various metal elements between TSP and soil were different.There was no significant correlation between TSP and surface soil and 40-60 cm depth soil of the elements in the same form.There are extremely significant correlations between the seven reducible forms heavy metal elements in TSP and the reducible Pb in 20-40 cm soil layer.(10)There was a significant correlation between heavy metals in the same form in the roots and in all soil layers.The correlation between roots and 20-40 cm soil layers was the highest.Compared to deeper soil layers.,The same form of heavy metal elements in the root and topsoil in the lower correlation.(11)There was a significant correlation between heavy metal elements of the same form in all organs.The correlation between the heavy metal elements in each form was as follows:leaf-branch> branch-stem > stem-bark> stem-root.