Study Of Different Varieties Of Festuca Arundinacea’s Rhizosphere Microecology And Remediation Effect On Petroleum Contaminated Soil

With the continuous development of oil extraction and processing industry, a large number of petroleum and its refined products entered the environment. Thus, petroleum has become a critical environmental problem now. Petroleum contaminated soil contains various harmful and chemically stable organic pollutants, which threats the ecological environment and even the human health. Therefore, seeking a cost-effective repair method is still a current research hotspot in the world.Compared with the traditional physical and chemical methods,phytoremediation removes organic pollutants by using the interaction between plant roots and soil microbes. Thus, the method generates no secondary pollution, is cost-effective and can produce the corresponding landscape ecological value. Festuca arundinacea (tall fescue) is a perennial herb with extensive roots, wide distribution and strong adaptability, which has a good remediation effect on petroleum contaminated soil among these repair plants. However, there are many varieties of F. arundinacea. Each variety’s living habit and remediation effect is different. The study of selecting high efficiency variety of F.arundinacea in remediation of petroleum contaminated soil is none.Therefore, it is necessary to screen efficient variety of F. arundinacea and conduct in-depth remediation mechanism in order to guide the remediation process more accurately and precisely.The study is based on pot experiment to illustrate the effects of different varieties of F. arundinacea on petroleum contaminated soil and the change of microbial community. The study also indicated the relationship between the dynamic changes of soil microbial communityand the removal efficiency of petroleum hydrocarbon during the restoration process. Through analyzing the effect of root exudates of F.arundinacea on remediation effect and microbial community change of polluted soil, the study analyzed the potential application value of root exudates in the process of actual repair and explored deeply the mechanism of combined remediation between plant and microorganism.The main result is as follows:(1) The result showed the effect of F. arundinacea was better than control treatment on repairing petroleum hydrocarbons, but there was significant difference of removal efficiency of petroleum in soil among different varieties. The removal rate of total petroleum hydrocarbons of the variety "Solar" was best with the removing rate of 49.4% and that of"Houndog 5" was worst with the removing rate of 18.7%. In addition, it has been found that the relative abundance of functional microorganisms associated with the contaminants degradation including Nocardia,Lysobacter, Pseudoxanthomonas, Mycobacterium, Rhodococcus and Planctomyces was significantly higher than the control group. But Houndog 5, Cochise and Green brooks have a lower relative abundance of these functional microorganisms than other plant treatments. In general,the removal effect of total petroleum hydrocarbons was positively correlated with the relative abundance of functional microbes in soil.(2) According to the previous study, the result further showed that the removal efficiency of different varieties of F. arundinacea was significant and there were different effects on structure and relative abundance of soil microbial community. The four cultivars including Pride, Rhizing star, Green brooks and Athera were filtrated for further research. The remediation effect of Rhizing star and Pride treatment on the total petroleum hydrocarbon was the highest, and that of Green brooks was the lowest. The number and relative activity of soil microbes increased first and then decreased during phytoremediation process.(3) Palmitic acid is one of the major organic acids among the root exudates of F. arundinacea, which can significantly promote the growth of functional microbes associated with degradation to promote the removal rate of petroleum contaminants. Different concentrations of organic acids can significantly promote the remediation of petroleum pollutants. However, the effects of different concentrations and components of organic acids and derivatives on the removing efficiency and soil microorganisms are also different. The relative abundance of degradation-related functional microbes increased in the treatment with better removal efficiency. It indicated that the specific root exudates, the composition and concentrations of organic acids would cause changes in the microbial community, which affects contaminant remediation.