Dramatic decoupling of nematode community responses to heavy metal pollution in high geological background soils

Soil nematodes play crucial roles as indicators of heavy metal pollution. However, despite extensive studies in anthropogenically contaminated soils, the ecological responses of nematode communities to heavy metals in high geological background areas remain poorly understood. In this study, soils from three types of high-background areas (which were dominated by chromium (Cr), mercury (Hg), and combined cadmium-arsenic (Cd-As) enrichment, respectively) were analyzed using 18S rDNA amplicon sequencing to characterize nematode community structure and its relationship with different metal forms. Principal coordinate analysis (PCoA) revealed distinct spatial differentiation in nematode community structure among regions enriched with different heavy metals. However, most nematode diversity indices showed no clear response to total or bioavailable metal concentrations. Comparable decoupling patterns were observed between nematode community interactions (including network topology metrics and module abundance) and metal concentrations. These results suggest that existing nematode-based bioindicators may not apply to naturally metal-rich environments. Collectively, our findings reveal a pronounced decoupling between nematode communities and heavy metal stress in the unique context of high geological background regions, highlighting the need to re-evaluate and adapt ecological risk assessment frameworks for such naturally metal-enriched environments.