Enhanced Phytoremediation Of Polychlorinated Biphenyls(PCBs) Contaminated Soil With Arbuscular Mycorrhizal Fungi

Polychlorinated Biphenyls(PCBs)are typical organic contaminants in the environment.It is indicated that plants and soil microorganisms have positive synergistic effect on remediation of PCBs contaminated soil,in which Arbuscular Mycorrhizal(AM)fungi play an important role.Greenhouse experiments were conducted to investigate the effect of AM fungi on remediation of PCBs contaminated soil under intercropping,crop rotation and biochar amendment and their related mechanisms.Ultrasonic extraction method and GC-MS were used to determine the soil PCBs concentrations.Real-Time Quantitative PCR,Terminal Restriction Fragment Length Polymorphism(T-RFLP)and high-throughput sequencing were used to measure the 16 S rDNA gene abundance and bacterial community composition,respectively.The main results were as follows.(1)Under the condition of AM fungi inoculation,intercropping significantly increased root mycorrhizal colonization rate and plant biomass of corn(p < 0.05),as well as soil available N content(p < 0.05).Significant difference of bacterial community composition was found among different treatments(p < 0.05).Compared with corn monoculture,corn/alfalfa intercropping significantly increased soil bacterial abundance(p< 0.05).The dissipation rates of total PCBs,as well as penta-chlorobiphenyls were significantly increased in the intercropping treatments when compared to corn monoculture(p < 0.05).Moreover,corn/ryegrass intercropping has significantly positive effect on the dissipation of Tri-chlorobiphenyls(p < 0.05).Non-metric multidimensional scaling(NMDS)result indicated that the PCBs homologues compositon were significantly correlated with the relative abundance of 128 bp and 148 bp T-RFs(p < 0.05).(2)Soil available N,P,K contents and pH decreased significantly(p < 0.05)but organic carbon content and root mycorrhizal colonization rate increased significantly(p <0.05)in crop rotation system.Compared to maize rotation,the root mycorrhizal colonization rate and plant biomass were significantly increased by alfalfa-maize rotation and ryegrass-maize rotation systems(p < 0.05).Moreover,alfalfa-maize rotation significantly enhanced the maize growth(p < 0.05).Significant differences of bacterial community compositions were found among different crop rotation systems,as well as bacterial abundance(p < 0.05).Crop rotation significantly enhanced soil PCBs dissipation rate(p < 0.05),but there was no significant difference among different treatments.Soil PCBs congener compositions were significantly correlated with the relative abundance of88 bp,128 bp,428 bp,436 bp,481 bp,488 bp,and 492 bp T-RFs(p < 0.05).(3)AM fungi inoculation significantly increased soil available P content,root mycorrhizal colonization rate and plant biomass.However,soil pH decreased significantly(p < 0.05).Biochar amendment significantly increased soil available P,K,organic matter content,soil pH,and root mycorrhizal colonization rate(p < 0.05).However,plant biomass was significantly decreased(p < 0.05).Amendment of small particle size biochar had the most significant negative effect on both organic carbon content and plant biomass(p <0.05).Both AM fungi and biochar had significant effect on soil bacterial community(p <0.05).Moreover,AM fungi and small particle size biochar had synergistic effects on the increase of 16 S rDNA gene abundance(p < 0.05).AM fungi and large particle size biochar had significantly positive effect on the dissipation of di-,tri-,tetra-chlorobiphenyls and total PCBs(p < 0.05),but there was no significant difference of PCBs congener compositions among different treatments.Stepwise regression analysis showed that tri-chlorobiphenyls dissipation was negatively correlated with the relative abundance of Planctomycetes,while penta-chlorobiphenyls dissipation was positively correlated with the relative abundance of Acidobacteria(p < 0.05).