Impact of Long-Term Mercury Contamination on the Rhizosphere Microbiota ofLotus tenuis: A Pathway to Resilience via Interkingdom Facilitation

The rhizosphere microbial communities ofLotus tenuisin Hg-contaminated soils demonstrate remarkable resilience, maintaining stable bacterial and fungal diversity across a broad contamination gradient (40–1964 mg Hg kg⁻¹ soil). Despite significant shifts in community structure compared to control communities from uncontaminated rhizosphere soil, alpha diversity remained largely unaffected, likely due to widespreadmerA-mediated bacterial detoxification. These findings align with the stress gradient hypothesis, indicating that facilitative microbial interactions drive adaptation under Hg stress rather than competition-driven diversity loss. The rhizosphere was enriched withMesorhizobiumsp., supporting nitrogen fixation,Pseudomonassp., a promising Hg-resistant bacterium, and various fungal partners enhancing plant tolerance to metal stress and drought. Key taxa included:Streptomycessp. (a biocontrol agent),Allorhizobium-Neorhizobium-Pararhizobium-Rhizobiumsp.,Shinellasp. (rhizobial plant-growth promoters),NocardioidesandSkermanellapotential metal- or aridity-resistant bacteria,Darksideasp.,Acrocalymma paeoniae (septate fungal endophytes that may promote plant stress tolerance),Mortierella alpina, Chaetosphaeronema (plant growth-promoting fungi), Humicolasp.,Vishniacozymasp. (potential pathogen suppressors). Septoglomus,Dioszegia, andArticulosporaemerged as potential candidates for microorganism-assisted phytoremediation. This study provides a field-based, long-term perspective on microbial adaptation to Hg stress, highlighting plant-driven recruitment of beneficial microbiota as a key mechanism for ecosystem resilience and soil recovery.