Co-occurring ferns orchestrate rhizosphere microbiome assembly driving divergent antimony adaptation at the XKS Mine, China

The adaptation of native plants to metalliferous environments is associated with intricate plant-microbiome interactions. However, how co-occurring species assemble distinct rhizosphere microbiomes under extreme heavy metal(loid) stress remains unclear. Here, we report a field-based example of ecological divergence among three fern species under extreme antimony (Sb) stress. The Sb-accumulator Pteris multifida showed rhizosphere characteristics consistent with a "Biogeochemical Reactor", including higher abundances of the aioA and anoA genes (3.12- and 4.54-fold, respectively) and elevated Sb(V) content, which were 26.41% and 30.04% higher than those in the excluders. These characteristics coincided with a specialized co-occurrence network which, under high Sb stress, exhibits reduced complexity (16.20% fewer nodes), but an increased proportion of positive interactions, rising from 44.66% to 50.70%. In contrast, the excluder species exhibited characteristics consistent with "Biogeochemical filters," including a 2.91-fold higher abundance of the arsC gene and a reduced proportion of bioavailable Sb. Partial least squares path modeling further identified fern functional type, defined by their Sb accumulation strategy, and Sb valence state as significant direct factors associated with root Sb accumulation. Our findings propose a field-based ecological framework in which host-mediated rhizosphere differentiation may contribute to divergent Sb adaptation strategies, providing a foundation for microbiome-assisted phytomanagement of Sb-contaminated soils.