Microecological mechanism of adaptation to heavy metal stress in Trifolium repens L. in an abandoned PbZn mining area

Previous studies have provided substantial evidence that plants actively recruit soil microorganisms to relieve abiotic stress. However, empirical evidence supporting this strategy in environments contaminated with heavy metals is limited. In this study, we conducted field sampling and indoor experiments to investigate the microecological mechanism by which Trifolium repens L., a dominant plant in abandoned mining areas, adapts to heavy metal stress. The results showed that high concentrations of heavy metals significantly altered the rhizosphere bacterial community structure of T. repens and significantly enriched Microbacterium. A representative amplicon sequence variant (strain M4) was successfully isolated by purification. In a plant growth promotion experiment, Microbacterium significantly increased the biomass and root length of T. repens under heavy metal stress. An untargeted metabolomics study in rhizosphere soil identified 71 differential metabolites at high concentrations of heavy metals, of which 37 were upregulated. Bacterial growth, biofilm, and chemotaxis experiments showed that L-proline and stigmasterol were key rhizosphere secretions of T. repens for recruiting Microbacterium. These findings provide new evidence for the recruitment of beneficial microorganisms by plants to adapt to heavy metal stress and will contribute to improving our ability to manipulate root microflora to promote plant growth in polluted environments.