Cadmium (Cd) contamination in rice (Oryza sativa L.) poses serious health risks for human, necessitating effective mitigation strategies. This study investigated the effects of Cd stress on iron (Fe), manganese (Mn), zinc (Zn), and Cd accumulation and translocation in rice varieties with high (MY46) or low (ZS97B) Cd accumulation capacities grown in acidic and alkaline soils. Results demonstrated that Cd stress significantly inhibited plant growth, reducing plant height, shoot biomass, and grain yield in both soil types. Cd accumulation increased in roots, shoots, and grains, while Fe, Mn, and Zn concentrations decreased markedly. Molecular analysis revealed upregulation of metal transporter genes (OsIRT1, OsNRAMP1, OsNRAMP5) and the vacuolar sequestration gene (OsHMA3) in roots under Cd exposure. The translocation factor (TF) values of Mn and Zn from root to shoot were reduced in acidic soils, whereas Mn and Zn TFs exhibited an increasing trend in alkaline soils despite Cd exposure. Furthermore, correlation analyses indicated Mn and Zn play crucial roles in suppressing Cd accumulation in both acidic and alkaline soils. These findings provide critical insights for developing soil-specific strategies to reduce Cd accumulation in rice through micronutrient management.

Single or combined plant growth-promoting bacteria (PGPB) strains were widely applied as microbial agents in cadmium (Cd) phytoextraction since they could promote plant growth and facilitate Cd uptake. However, the distinct functional effects between single and combined inoculants have not yet been elucidated. In this study, a field experiment was conducted with single, double and triple inoculants to clarify their divergent impacts on plant growth, Cd uptake and accumulation at different growth stages of Brassica juncea L. by three different PGPB strains (Cupriavidus SaCR1, Burkholdria SaMR10 and Sphingomonas SaMR12). The results show that SaCR1 + SaMR10 + SaMR12 combined inoculants were more effective for growth promotion at the bud stage, flowering stage, and mature stage. Single/combined PGPB agents of SaMR12 and SaMR10 were more efficient for Cd uptake promotion. In addition, SaMR10 + SaMR12 combined the inoculants greatly facilitated Cd uptake and accumulation in shoots, and enhanced the straw Cd extraction rates by 156%. Therefore, it is concluded that the application of PGPB inoculants elevated Cd phytoextraction efficiency, and the combined inoculants were more conductive than single inoculants. These results enriched the existing understanding of PGPB agents and provided technical support for the further exploration of PGPB interacting mechanisms strains on plant growth and Cd phytoextraction, which helped establish an efficient plant–microbe combined phytoremediation system and augment the phytoextraction efficiency in Cd-contaminated farmlands.

Cadmium (Cd) accumulation in rice poses a serious threat to food safety. While soil amendments with manganese (Mn) and zinc (Zn) can reduce Cd accumulation in rice, their distinct modes of action remain unclear, hindering the optimization of mitigation strategies. This study aimed to clarify the differential physiological and molecular mechanisms by which Mn and Zn mitigate Cd toxicity in rice. In a pot experiment using two rice genotypes with differing Cd-accumulation capacities, plants were exposed to Cd stress alongside MnSO₄ (150 and 300 mg.kg⁻¹) or ZnSO₄ (50 and 100 mg.kg⁻¹) amendments. Results showed that although soil-available Cd content was unaffected, both treatments differentially reduced Cd concentrations in plant tissues. Mn and Zn application reduced grain Cd by 26.46-33.11% and 43.67-52.60%, respectively. Notably, Mn strongly inhibited the root-to-shoot transport of Cd, reducing the translocation factor by up to 56.46% and 47.30% in the two genotypes. Conversely, a low dose of Zn increased this transport by 1.54- to 1.76-fold. Correlation analyses indicated that Zn levels in soil and rice tissues were negatively associated with root Cd, whereas Mn levels were negatively correlated with shoot Cd. Both amendments alleviated root oxidative stress and enhanced antioxidant enzyme activity. Furthermore, they differentially regulated the expression of key genes involved in Cd transport. This study demonstrates that while both Mn and Zn mitigate Cd accumulation, their dominant mechanisms differ: Zn primarily reduces Cd entry and enhances its retention in roots, while Mn predominantly restricts its upward movement to shoots. These insights provide a scientific foundation for developing tailored micronutrient management strategies to improve rice safety in Cd-contaminated environments.