Phenanthrene Stress On Dynamic Characteristics And Root Activity Of Koelreuteria Paniculata And Cinnamomum Camphora

With the development of industrialization and the increasing level of urbanization,the situation of land environmental pollution in China has become extremely serious.Recently,soil bioremediation technologies has been one of the most effective environmental restoration method,of which utilize plants to degrade soil organic pollutants and to repair environmental pollution.In this study,we selected Koelreuteria paniculata and Cinnamomum camphora,which are common afforest tree in southern China,as the research tree species.Meanwhile,phenanthrene was selected as the representative of polycyclic aromatic hydrocarbons.The concentration of phenanthrene was set as LO:0 mg·kg^-1,L1:100 mg·kg^-1,and L2:1000 mg·kg^-1 to calculate the total carbon,total nitrogen and root activity in the root exudates.Then,the dynamic characteristics of the root exudates were discussed with representative days of each quarter sampling.The seasonal dynamics of total carbon,total nitrogen content and root activity in root exudates were analyzed and compared with the dynamic characteristics of root exudates.The response mechanism of root exudates was studied under phenanthrene stress,with a view to providing theoretical reference for phytoremediation of PAHs contaminated soils.Finally,it is expected to provide some significant guidance for the layout,construction and management of urban forest.The research results are as the following:The content of TC and TOC in the root exudates of Koelreuteria paniculata system was mostly higher than those of Cinnamomum camphora’s.When phenanthrene was at L0,the content of TC in the the root exudates of Koelreuteria paniculata was lower than Cinnamomum camphora in the first,second and fourth season,and the remainder were higher than Cinnamomum camphora’s in each season,especially at the L2 treatment level.There were significant differences in the second season of two species（P<0.01）,the remaining three season also showed significant differences（P<0.05）;the contents of TOC in the root exudates of Koelreuteria paniculata in four seasons were all lower than Cinnamomum camphora’s at the L0 processing level in the first season and the second season,and the remainder were higher than Cinnamomum camphora’s,especially at L2 processing level.There were significant differences in the second season of two species（P<0.01）,and there were significant differences in the first and fourth season（P<0.05）;the content of TN in Koelreuteria paniculata system was lower than Cinnamomum camphora’s at the L0 treatment level in the second season,and were higher than Cinnamomum camphora’s at other seasons of each level.There were significant differences（P<0.01）under the L2 treatment level in the first season,and there were significant differences in the L1 and L2 treatment levels in the third season（P<0.05）.The department total absorption area and active absorption area of Koelreuteria paniculata were lower than Cinnamomum camphora’s in the first quarter of the L0 treatment level,the second quarter of the L2 treatment level,and the third quarter of the L0,L1 treatment level.In all the four seasons,the contents of TC,TOC and TN in root exudates of Koelreuteria paniculata were higher than those of Cinnamomum camphora at each treatment level,which indicated that the secretion of root system of Koelreuteria paniculata was higher than that of Cinnamomum camphora.The total area and active area of Koelreuteria paniculata root at L1 and L2 was higher than the Cinnamomum camphora’s,indication of higher root activity of Koelreuteria paniculata than that of Cinnamomum camphora.The results showed that the addition of phragmites australis showed a certain tolerance to the addition of phenanthrene,while the roots of Cinnamomum camphora showed stress of phenanthrene.Therefore,Koelreuteria paniculata is more tolerant to phenanthrene than Cinnamomum camphora did.