Mining and smelting activities are the major sources of antimony (Sb) contamination. The soil around Xikuangshan (XKS), one of the largest Sb mines in the world, has been contaminated with high concentrations of Sb and other associated metals, and has attracted extensive scholarly attention. Phytoremediation is considered a promising method for removing heavy metals, and the diversity and structure of rhizosphere microorganisms may change during the phytoremediation process. The rhizosphere microbiome is involved in soil energy transfer, nutrient cycling, and resistance and detoxification of metal elements. Thus, changes in this microbiome are worthy of investigation using high-throughput sequencing techniques. Our study in Changlongjie and Lianmeng around XKS revealed that microbial diversity indices in the rhizospheres of Broussonetia papyrifera and Ligustrum lucidum were significantly higher than in bulk soil, indicating that plants affect microbial communities. Additionally, most of the bacteria that were enriched in the rhizosphere belonged to the Proteobacteria, Acidobacteria, Actinobacteria, and Bacteroidetes. In Changlongjie and Lianmeng, the diversity and abundance of the microbial community in the B. papyrifera rhizosphere were higher than in L. lucidum. In parallel, the soil pH of the B. papyrifera rhizosphere increased significantly in acidic soil and decreased significantly in near-neutral soil. Redundancy analyses indicated that pH was likely the main factor affecting the overall bacterial community compositions, followed by moisture content, Sb, arsenic (As), and chromium (Cr).

Understanding how patterns of recovery and geological conditions affect microbial communities is important for determining the stability of karst ecosystems. Here, we investigated the diversity and composition of microorganisms in karst and non-karst environments under natural restoration and artificial rehabilitation conditions. The results showed no significant differences in soil microbial diversity, but the microbial communities associated with geological conditions and tree species differed significantly. Variation partitioning analysis (VPA) showed that a total of 77.3% of the variation in bacteria and a total of 69.3% of the variation in fungi could be explained by vegetation type and geological background. There were significant differences in six bacterial classes (Actinobacteria, Alphaproteobacteria, Ktedonobacteria, TK10, Gammaproteobacteria, and Anaerolineae) and nine fungal classes (Eurotiomycetes, Agaricomycetes, unclassified _p_Ascomycota, Sordariomycetes, Tremellomycetes, norank_k_Fungi, Pezizomycetes, Leotiomycetes and Archaeorhizomycetes) among the soils collected from six plots. A Spearman correlation heatmap showed that the microbial community was affected by the major soil properties. Principal coordinates analysis indicated that the microbial community of Pinus yunnanensis in the artificial forest, which was established for the protection of the environment was most similar to that in the natural secondary forest in the karst ecosystem. These findings further our understanding of microbial responses to vegetation restoration and geological conditions.

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