Role of Sedum alfredii and soil microbes in the remediation of ultra-high content heavy metals contaminated soil

Ultra-high content of heavy metals (UHHMs) poses a threat to soil health and agricultural products safety, in turn causing harm to human health through the food chain. Phytoremediation has proven to be an effective technique for restoration of soil contaminated with a single or several conventional content of heavy metals, whereas the effectiveness of phytoremediation for UHHMs-contaminated soil is unclear. In this study, we investigated the effectiveness of phytoremediation for UHHMs-contaminated soil and the role of soil microbes in the process of phytoremediation. Results showed that the Sedum alfredii grew well in UHHMs-contaminated soil, although the shoot height, biomass, and accumulation of heavy metals were slightly reduced due to the stress of UHHMs. Soil microbiome analysis demonstrated that both the number and diversity of microbes decreased in UHHMs-contaminated soil. However, the dominant species Patescibacteria proliferated to varying degrees under the exposure of various UHHMs. Patescibacteria is closely related to the functional genes regarding transport of various heavy metals. Given that Patescibacteria exhibits a strong migration ability in soil, it is likely involved in the transport of various heavy metals from the bulk soil to the rhizosphere. This enhanced the availability of heavy metals in the rhizosphere, which in turn improved the phytoremediation efficiency of the Sedum alfredii. This was further confirmed by structural equation modeling analysis and microbial phenotypes prediction. Findings suggest that using Sedum alfredii to remedy UHHMs-contaminated soil is feasible owing to the facilitation by soil microbes.