Multi-factor influences on potentially toxic element speciation and crop uptake in high-background soils of Southwest China

High background values of potentially toxic elements in soils do not always necessitate high ecological risks, yet the decoupling mechanisms remain constrained in sloping farmlands. Here, eight elements were investigated in rhizosphere soils, maize kernels, and konjac corms from Southwest China. Results indicated that soils were acidic and enriched in Chromium, Zinc, Copper, Nickel, Arsenic, and Cadmium relative to the regional background. Sequential extraction showed Cadmium was dominated by active fractions averaging 36.3%, whereas Arsenic was predominantly residual. Konjac corms exhibited significantly higher bioaccumulation than maize kernels, with a Cadmium bioaccumulation factor of 2.93 compared to 0.024 for maize. Structural equation modeling revealed distinct accumulation pathways: soil water-soluble Cadmium directly drove maize kernel Cadmium with a standardized path coefficient of 0.447. Conversely, konjac corm Cadmium was strongly controlled by corm Zinc with a coefficient of 0.959, evidencing synergistic uptake. Furthermore, pH, CaO, Nickel, and Manganese oxides acted as key regulators suppressing Cadmium lability. Proximity to coal mining areas further associated with elevated element concentrations and mobility. These findings quantify multi-factor controls on crop uptake and highlight that species-specific accumulation mechanisms must be prioritized for safe agricultural management in high-background regions.