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

Abstract

The rhizosphere microbial communities of Lotus tenuis in Hg-contaminated soils demonstrate remarkable resilience, maintaining stable bacterial and fungal diversity across a broad contamination gradient (40-1964 mg Hg kg-{superscript 1} soil). Despite significant shifts in community structure compared to control communities from uncontaminated rhizosphere soil, alpha diversity remained largely unaffected, likely due to widespread merA-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 with Mesorhizobium sp., supporting nitrogen fixation, Pseudomonas sp., a promising Hg-resistant bacterium, and various fungal partners enhancing plant tolerance to metal stress and drought. Key taxa included: Streptomyces sp. (a biocontrol agent), Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium sp., Shinella sp. (rhizobial plant-growth promoters), Nocardioides and Skermanella potential metal- or aridity-resistant bacteria, Darksidea sp., Acrocalymma paeoniae (septate fungal endophytes that may promote plant stress tolerance), Mortierella alpina, Chaetosphaeronema (plant growth-promoting fungi), Humicola sp., Vishniacozyma sp. (potential pathogen suppressors). Septoglomus, Dioszegia, and Articulospora emerged 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.