Physicochemical Aspects And Microbial Communities Of Iron Mine Tailings By Integrated Restoration With Robinia Pseudoacacia-Ryegrass-Trifolium Repens

The tailings pond dam broken occurs frequently and brings great harm.Therefore,it is urgent to stabilize tailings,and phytoremediation is one of the best ways.In this paper,the iron tailings phytoremediation test was carried out by planting Robinia pseudoacacia-Ryegrass-Trifolium repens in pot experiment.The physicochemical property,enzymatic activity and microbial population were determined.The genetic diversity of bacteria isolated from different treatment was performed by BOX–PCR,and the phylogeny of representative strains was done by 16S r DNA sequencing techniquet.Then the soil microbial communities at different periods under different processing tailings were analyzed by the Illumina Miseq sequencing technologies.The results were as followings:1.The phytoremediation treatment of Robinia pseudoacacia-Ryegrass-Trifolium repens could decrease the pH of the remediation mixture significantly,and increased the content of available phosphorus and organic matter,while maintain the stable growth of total nitrogen and the organic matter.The pH value of C1,C2 tailings sample decreased from7.90 at the initial stage to 7.50 and 7.51,while the pH value of C0（control tailings）was still 7.98.The nutrient content of C1 and C2 reached a high level at 360d,total nitrogen was 1.09 g·kg^-1and 0.95 g·kg^-1,available nitrogen was 85.67 mg·kg^-1and 69.67 mg·kg^-1,available phosphorus was 43.90 mg·kg^-1and 66.48 mg·kg^-1,available potassium was154.39 mg·kg^-1and 160.45 mg·kg^-1,organic matter was 26.83 g·kg^-1and 23.53 g·kg^-1,respectively.Both C1 and C2 were significantly higher than C0 of the same period,and not significant difference from C3 and C4.2.The activity of urease,phosphatase and catalase increased with the prolonging of treating time.At 540 d,the urease activity of C1 and C2 was 1.0985 mg H₂O₂·g^-1·20min^-1and 1.1040 mg H₂O₂·g^-1·20min^-1,phosphatase activity was 4.5034 mg·g^-1·24h^-1and 7.5797mg·g^-1·24h^-1,and catalase activity was 1.0883 mg H₂O₂·g^-1·20min^-1and 1.5747mg H₂O₂·g^-1·20min^-1,respectively.All the tested enzymatic activities of C1 and C2 were significantly higher than those of C0,and the differences with C3 and C4 were reduced.Besides,with the extension of remediation time,the number of bacteria in C1 and C2tailings samples was more than doubled.The number of fungi increased significantly at360d,and each treatment increased by an order of magnitude,while the number of fungi in C2 and C3 was the largest in the treatment of biological matrix flowerpots.The number of actinomycetes in each treatment increased by more than an order of magnitude from 180d to 360d,and reached 18.75×10⁵cfu·g^-1～35.64×10⁵cfu·g^-1at 540 d,except for C0.3.A total of 173 bacterial strains were isolated from tailings and soil samples.BOX-PCR analysis and 16S r DNA sequencing showed that the bacterial flora and genetic diversity from tailings and soil samples were significantly different at three treatment time.A total of 16 strains,include WTB2,WTB3 and WTB7,which belonged to Rhizobium,Ensifer,Azotobacter and Phyllobacterium,could fix nitrogen by themselves or had the ability of symbiotic nitrogen fixation with legumes.They played an important role in the bioremediation of tailing sands.4.The bacterial and fungal community structures in tailings and soil samples were analyzed by Miseq sequencing.The results showed that Proteobacteria,Chloroflexi,Actinobacteria,Acidobacteria and Gemmatimonadetes were the dominant bacterial groups,while Ascomycota,Basidiomycota,Zygomycota and Chytridiomycota were the dominant fungal groups at the phylum level.At the genus level,Pseudomonas,Sphingomonas,Variibacter,MND1 and Nocardioides were the dominant bacterial groups,while Bullera,Mortierella,Acremonium,Trichoderma and Mycothermus are the dominant fungal groups.Moreover,the abundance of dominant microorganisms in tailings and soil was significantly diverse at different treatment time.The NMDS analysis of bacteria and fungi results show that the samples were separated by NMDS2 axis for 360d and 540d.It showed that the bacterial and fungal communities of the same sample were quite different in different periods.The RDA analysis of bacteria and fungi showed that pH value was negatively correlated with tailings and soil samples treated by planting plants,and positively correlated with tailings of blank control,indicating that pH was the main driving factor of microbial community change in the treatment system.