Spatial Variations Of Nitrogen And Heavy Metals In The Soil And Tress Of Highway Forest Belt

This thesis focuses on the study of the spatial variations of total N, ¹⁵N natural abundance(δ¹⁵N) and heavy metals in the soil and Poplar of highway forest belt at 312 national highway in Nanjing. The results will be used as a basis for the designing of planting models. The main results are as follows:(1)The content of total N,δ¹⁵N has reduced as the increase of the distance from the highway. This is mainly caused by the atmospheric NOx pollution from the highway.(2)The contents of total N in soil are no good regularity with the change of the distance. It is the reason that the contents of total N in the soil may be decided by many relevant factors.(3)The contents of total N andδ¹⁵N in root xylem and its cortex at the distance of 80 m are higher than these at the distance of 10 m, but the contents of total N andδ¹⁵N in trunk cortex and its xylem A,B are just the contrary.(4)The contents of Zn,Cr,Pb,Cd in leaves show a downtrend along with the distance from the highway increasing. By the principal component analysis, the accumulation amounts of heavy metals in the leaves are in order of 5m>10m>20m>40m>60m>80m>100m.(5)Along with the distance increasing the contents of Cd,Mn,Pb in soil show the same increasing tendency. The content of Zn has the gradual decreasing trend. The impact evaluation of the pollution of heavy metals in soil reveals that the pollution indexes of Fe, Pb, Cr are all less than 1.0,which belong to the Gradeâ… (clean standard). The pollution of Cu, Zn, Mn in soil mostly are Gradeâ…¡(light pollution). But the pollution index of Cd has come up to Gradeâ…£(seriously pollution).(6)The accumulation amounts of heavy metals in different organs of the Poplar at the distance of 10 m and 80 m have the same variation trend. Cd: the accumulation amounts in leaves>in cortexes>in xylem; Cr: the accumulation amounts in root's cortexes>in xylems; Cu: the accumulation amounts in leaves>in cortexes>in xylems; Fe: the accumulation amounts in root's cortexes>in leaves>in xylems; Mn: the accumulation amounts in leaves>in cortexes>in xylems; Pb: the accumulation amounts in leaves>in roots; Zn: the accumulation amounts in cortexes>in xylems.