Zinc-assisted cadmium phytoremediation and safe rice production in a Sedum alfredii Hance-rice rotation system

Fertilization in hyperaccumulator-crop rotation systems provides an effective strategy for enhancing cadmium (Cd) phytoremediation and mitigating food safety risks in contaminated agricultural soils. Accordingly, we assessed the effects of soil application of zinc (Zn) fertilizer (EDTA-Zn, ZnSO₄, and ZnO NPs) during S. alfredii planting on Cd phytoextraction, rice productivity, and rice grain safety in the S. alfredii- rice rotation system. Results showed that the application of Zn fertilizers increased S. alfredii shoot biomass (21.7%–33.0%) and Cd concentration (20.1%–28.4%), thereby improving phytoextraction efficiency (28.8%–56.5%) relative to the control. After the harvest of S. alfredii , residual soil Zn significantly reduced Cd accumulation in aboveground rice tissues at both the tillering and maturity stages. Specifically, Cd concentrations in brown rice were significantly decreased by 11.3%–43.2%. Soil physicochemical analysis indicated that Zn treatments influenced Cd uptake in S. alfredii and rice by altering soil Cd bioavailability. Moreover, Zn application reduced health risks associated with Cd exposure by 19.7%–45.8% based on Cd bioaccessibility in polished rice. Treatments with ZnSO₄ and ZnO NPs also enhanced rice yield and improved nutritional traits, including grain Zn concentration and amylose content. Overall, ZnSO₄ was identified as the most suitable fertilizer for improving both phytoremediation efficiency and rice production safety in the S. alfredii- rice rotation system.