Responses of soil microbes to antimony stress and coupled nutrient cycling in karst mining areas of Southwest China

Persistent and poorly mobile heavy metals in soil present a widespread environmental challenge. Among these, antimony (Sb) is a contaminant of emerging concern whose transformation and migration in soil require further investigation to inform effective remediation strategies. Microbial processes are central to these dynamics, yet the mechanisms underlying Sb-microbe interactions remain poorly defined. In this study, we used integrated geochemical and metagenomic analyses to assess Sb contamination and microbial community responses systematically in an abandoned Sb mining area in Southwest China. The data reveal how microbial communities respond to low and moderate levels of Sb contamination. Contamination was highest in the mining area, followed by the smelting and tailings areas; the control area exhibited the lowest levels. Community structure analysis revealed significant enrichment of Thiobacillus, Geothrix, and Anaeromyxobacter in the mining area, while Nocardioides and Sphingomonas were more abundant in the smelting area. Bradyrhizobium dominated in the control area. These patterns reflect distinct microbial responses to the Sb contamination gradient. Critically, partial least squares path modeling revealed that Sb contamination did not directly affect microbial α-diversity. Instead, its influence was indirectly mediated through disruptions in sulfur cycling functions-a novel finding highlighting the indirect ecological impact of Sb. Sb, along with co-occurring copper, may drive adaptive microbial succession by interfering with sulfate respiration. This process enriches microbial groups with sulfur-cycling-related detoxification functions, resulting in simplified community structure and reduced diversity. Thus, the primary mechanism by which Sb alters microbial communities in karst soils is indirect, operating via perturbation of the sulfur cycle rather than direct toxicity. These findings offer a theoretical basis for developing targeted microbial remediation strategies and restoring ecological functions in Sb-contaminated environments by regulating key elemental cycles.