Responses of rhizosphere bacterial communities, their functions and their network interactions to Cd stress under phytostabilization by Miscanthus spp.

Miscanthus has good tolerance to heavy metals (HMs) and has received increasing attention in studies of HM-contaminated soil remediation. In this study, four Miscanthus cultivars (M. lutarioriparius Xiangnadi NO4, M. sinensis Xiangmang NO1, M. lutarioriparius × M. sinensis hybrid Xiangzamang NO1, and M. floridulus Wujiemang NO1) that grow in China were studied. Their tolerance and enrichment abilities in soils containing 50 mg kg cadmium (Cd) and the structure and function of their rhizosphere bacterial communities during the remediation process were analyzed. The results exhibiting a tolerance index (TI) higher than 75 in roots and the aboveground parts (TI > 60, indicating highly tolerant plants) indicated that all four Miscanthus cultivars were tolerant to high Cd concentrations. Moreover, Cd was mainly enriched in roots, the translocation ability from roots to aboveground parts was weak, and the four cultivars exhibited phytostabilization ability in Cd-contaminated soils. High-throughput sequencing (HTS) analysis showed that the Miscanthus rhizosphere bacterial community comprised 33 phyla and 446 genera, including plant growth-promoting rhizobacteria (PGPRs), such as Bacillus, Sphingomonas, and Mesorhizobium. The addition of Cd affected the Miscanthus rhizosphere bacterial community and reduced community diversity. Phylogenetic molecular ecological networks (pMENs) indicated that Cd addition reduced interactions between Miscanthus rhizosphere bacteria and thereby led to a simpler network structure, increased the number of negative-correlation links, enhanced the competition between rhizosphere bacterial species, reduced the number of key bacteria, and changed the composition of those bacteria. PICRUSt functional predictive analysis indicated that Cd stress reduced soil bacterial functions in the Miscanthus rhizosphere. The results of this study provide a basis for the remediation of Cd-contaminated soils by Miscanthus and provide a reference for the subsequent regulation of Miscanthus remediation efficiency by PGPRs or key bacteria.