Arsenic and Iron Gradients Orchestrate Microbial Community Restructuring and Functional Shifts in Long-term Abandoned Pb-Zn Tailings

Historic Pb–Zn smelting produces complex geochemical gradients around the tailing regions, yet the ecological strategies enabling microbial persistence in these long-term polluted sites remain largely unresolved. This research employed shotgun metagenomics to investigate whether soil microbiomes can structurally and functionally reshape along a contamination gradient. The arsenic (As) and iron (Fe), instead of Pb or Zn, were probably the most important environmental drivers of community differentiation. Notably, the community structure was reorganized after severe contamination. Furthermore, significant increases were noted in evenness without impacting taxa richness. The sensitive Chloroflexota and Actinomycetota were replaced by resilient Pseudomonadota , Myxococcota , Nitrospirota , Verrucomicrobiota , and Thermodesulfobacteriota . The KEGG enrichment implies a fundamental functional trade-off: microbial strategies appear to shift from "resource-foraging" (motility and chemotaxis) in less polluted soils to "stress-maintenance" (DNA repair and central metabolism) in heavily contaminated areas. Moreover, the widespread "As–Fe axis" seems to favour certain adaptive characteristics. The study shows that across the gradient, a universal resistance baseline constituted by arsC / arsR / arsM , while acr3 / arsB rose markedly in the most contaminated soils. Functionally, acid-tolerant families such as Nitrospiraceae , Acetobacteraceae and Anaeromyxobacteraceae coupled their arsenic-related capacities with nitrogen cycling, iron reduction and organic matter turnover, thus maintaining essential biogeochemical processes under extreme contamination. Based on these findings, it appears that microbial adaptation in tailings-affected soils is likely driven by niche-specific genomic modulation and energetic constraints rather than simple toxicity-induced diversity loss. • As and Fe gradients appear to reorganize the soil microbial community without changing richness. • Genomic data suggest a functional trade-off from "resource-foraging" to "stress-maintenance" strategies. • The As–Fe axis likely facilitates the niche-specific enrichment of acr3 genes in acid-tolerant taxa.