| In this paper,the tree rings and root soil of Pinus massoniana Lambert ? Robinia pseudoacacia Linnaeus?Pistacia chinensis Bunge?Ailanthus altissima(Miller)Swingle?Ulmus pumila Linnaeus in the Qixiashan Forest Park were studied.In addition,contents of Cd,Cr,Cu,Fe,Ni,Mn,Pb,Zn and their dynamic changes were also researched by means of spatial method instead of time method in this paper.Tree species with strong capacity in repairing contaminated soils were found out,and suitable trees vector for recording the history of soil upon heavy metal pollution in Qixia Mountain were screened out.The history of the heavy metal pollution of soil in Qixia Mountain for the recent 20 years(1996~2015)was reconstructed.The discussion of this issue can provide theoretical basis of environmental protection measures for the similar forest parks which also suffer from heavy metal pollution,thus offering guidance to local soil repairing work.The main conclusions are as follows:(1)The abilities of absorption of eight heavy metal elements in five trees was compared with a standard of absorption coefficient(Kf)in the Qixiashan Forest Park,to screen the suitable trees for repairing soil heavy metal pollution.The results show that the abilities of a single tree species in absorbing different heavy metal elements was different.The abilities of five kinds of trees in absorbing one same heavy metal element was different neither.The absorptive capacities of Ni,Pb,Zn,Cd and Cu in Robinia pseudoacacia was stronger than that in the other four species,and the ability of Robinia pseudoacacia in repairing heavy soil pollution was better.The absorptive capacities of Cr,Zn,Ni in Ailanthus altissima was better than other four species.The absorptive capacities of Cu,Cr,Mn and Pb in Ulmus pumila was better than other four species.The absorptive capacity of Cd in Pinus massoniana was stronger than other four species.The absorptive capacities of Pistacia chinensis of Cd,Cu,Fe,Mn,Ni,Pb,Zn was weaker than other four species,it may not be suitable plant material for repairing contaminated soil with heavy metal pollution.(2)The abilities of absorption of three Robinia pseudoacacia,which were in three age groups and were grown in different environments in 15 years(1990~2004),for eight heavy metal elements was compared to further understand its discrepancies of the abilities regarding the age of the tree,by means of Duncan's multiple range test and LSD(Least-Significant Difference).It can be found that the greater the age of the Robinia pseudoacacia,the stronger the absorption capacity.45 years old>35 years old >25 years old,and the absorptive capacities of Cd,Ni,Mn and Pb of the 45-year-old Robinia pseudoacacia was significantly stronger than that of the other two.In the practical application of ecological restoration,the longer the planting time of Robinia pseudoacacia,the better the effect of repairing soil pollution.(3)The correlation analysis of eight heavy metal elements in five tree rings was carried out by Pearson correlation analysis,in order to explore the origin and cause of the heavy metal elements in the tree ring.The preliminary conclusions are as follows,In general,the synergistic effect of the eight heavy metal elements in the five tree rings was more obvious,which means that the source is consistent.There were significant synergistic effects between Ni and Cr and other elements in tree ring of Ailanthus altissima.There were synergistic effects between Cr and Cu,Fe,Ni,Mn,Zn,Zn and Cd,Cr,Fe,Ni,Mn and Pb in tree ring of Robinia pseudoacacia.There were synergistic effects between Cd and Fe,Zn,Pb in tree ring of Pistacia chinensis,however,there were antagonistic action between Cd and Ni.There were synergistic effects between Cu and Fe,Ni,Mn and Zn in tree ring of Pinus massoniana,however,there were antagonistic action between Cd and Cu,Mn and Pb.There was certain degree of antagonism between Cd and Ni,Pb in tree ring of Ulmus pumila.(4)The evaluation of heavy metal pollution was carried out in the study area by the single factor index evaluation method,so as to explore the status of heavy metal pollution and the history of pollution in the soil of Qixia Mountain.Dynamic variation of eight kinds of heavy metal elements in the past 30 years(1986~2015)of five tree rings in Qixia Mountain were studied.The results show that there were serious pollution of Cd,Cu,Fe,Ni,Pb and Zn in the Qixiashan Forest Park,and there was a high degree of pollution in Cd,Pb and Zn.Due to the influence of soil pollution events in Qixia Mountain,there were significant differences in the contents of heavy metal elements in different tree species in different time periods.The content of different heavy metal elements in a single tree species are also different in different time periods.(5)Five tree of different species with similar ages and three Robinia pseudoacacia with the same age but different habitats were studied in the Qixia Mountain,so that find out the relationship between the heavy metal content of soil and the heavy metal content of tree ring.Thus,the correlation analysis between heavy metals and soil heavy metals was carried out.The preliminary conclusion is that the contents of eight heavy metals in the five trees and three Robinia pseudoacacia were in line with the linear correlation.There was a positive correlation between the age and heavy metal content of the tree rings,and it was not affected by the tree species and growth environment.(6)The contents of four heavy metals,Cd,Cr,Cu and Zn,in the tree rings of the past 20 years in three 45-year-old Robinia pseudoacacia in Qixia Mountain were studied by logarithmic linearity,so as to further explore the trend and characteristics of soil pollution in Qixia Mountain,and based on the high sensitivity of Cd,Cr,Cu and Zn in Robinia pseudoacacia.The pollution history and dynamic changes of Cd,Cr,Cu and Zn in the soil were retrieved in combination with the historical content of Robinia pseudoacacia.The preliminary conclusions are as follows,The content of Cd,Cr,Cu and Zn in the Robinia pseudoacacia rings and the content of elements in the soil satisfy the logarithmic linear correlation pattern:lgC'=algC+b.In the past 20 years,the content of Cd in the soil of Qixia Mountain has been stable at a low level,and the overall trend was increasing.Content of Cr in the soil remained at a high level,and the fluctuations are large with multiple peaks.The content of Cu in the soil was relatively stable,and the trend of the total content of Zn in the soil was not fluctuated in the past 20 years,and there was no obvious increase or decrease trend in the past 20 years.Compared with the other four trees,Robinia pseudoacacia is more suitable as a biological record carrier to reconstruct the soil pollution history of Cd,Cr,Cu and Zn. |
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