Abstract:

Objective: This study aims to explore the effects of planting Pinus elliottii, Cunninghamia lanceolata and Alnus cremastogyne on the soil heavy metal mass fraction and microbial community composition in the iron tailing mine area of Jiulong, and to provide reliable scientific data and theoretical basis for vegetation restoration in this mine area and areas with similar stand conditions. Method: Rhizosphere and non-rhizosphere soil samples and root, stem and leaf samples of Pinus elliottii, Cunninghamia lanceolata and Alnus cremastogyne were treated by microwave digestion. The heavy metal mass fractions of the samples were determined by ICP and AAS. Macrogenomics sequencing was used to analyze the rhizosphere and non-rhizosphere soil samples of the three tree species and to investigate the composition of microbial communities in the corresponding soils of the three tree species. Result: 1) The biotransfer coefficients of all three species were greater than 1 for Hg, Cu, Pb, and Zn, and less than 1 for Cr, indicating their strong transfer ability to Hg, Cu, Pb, and Zn and weak transfer ability to Cr. The biotransfer coefficients of Cunninghamia lanceolata to As were greater than 1, indicating that the transfer ability of Cunninghamia lanceolata to As was strong. 2) The bioenrichment coefficients of Cunninghamia lanceolata for Hg and Pb were all greater than 1, indicating that Cunninghamia lanceolata has good bioenrichment ability for Hg and Pb. Compared with other heavy metals, Pinus elliottii had the highest bioenrichment coefficients for Hg and Pb, and Alnus cremastogyne had the highest bioenrichment coefficients for Zn, indicating that Pinus elliottii had better bioenrichment ability for Hg and Pb, and Alnus cremastogyne had better bioenrichment ability for Zn. 3)At the phylum level, the phylum with the highest relative abundance in J1 was Acidobacteria (45.55%), followed by Proteobacteria (12.11%). The most abundant phylum in J2, J3, J4, J5, and J6 was Proteobacteria, with an abundance range of 22.72% to 44.56%. The next most abundant phylum was Acidobacteria, with an abundance range of 13.49% to 16.56%. At the genus level, the dominant genera in J1 were Bradyrhizobium and Ktedonobacter spp. The dominant genera with the highest relative abundance percentages in J2, J3, J4, J5 and J6 were Bradyrhizobium and Sphingomonas spp. Conclusion: 1) Pinus elliottii, Cunninghamia lanceolata and Alnus cremastogyne all had a strong transfer ability for Hg, Cu, Pb and Zn, and all had a weak transfer ability for Cr. The transfer ability of Cunninghamia lanceolata to As was stronger. Pinus elliottii and Cunninghamia lanceolata have better bioenrichment ability for Hg and Pb, and Alnus cremastogyne has better bioenrichment ability for Zn. Pinus elliottii and Cunninghamia lanceolata can be used as pioneer trees for Hg and Pb restoration, and Alnus cremastogyne can be used as restoration trees for Zn with their intercropping. 2) Based on the analysis at the two taxonomic levels of phylum and genus, the dominant microbial communities in the rhizosphere and non-rhizosphere soils of the three tree species were all in the phylum Proteobacteria, and the planting of all three tree species promoted the increase in the relative abundance of microorganisms of the phylum Proteobacteria in soil. Phylum Proteobacteria can improve the absorption of heavy metals by plants and promote plant growth. The two complement each other and promote each other. It can effectively improve the absorption efficiency of heavy metals by plants.

Key words: metagenomic sequencing, iron ore tailing, heavy metal pollution, phytoremediation effect, microbial community composition