Dose-dependent zinc application modulates cadmium accumulation in wheat via rhizosphere metabolites and bacterial...

Zinc (Zn) application in appropriate dose effectively reduces cadmium (Cd) accumulation in wheat plants, but the mechanisms by which different Zn rates regulate Cd accumulation via rhizosphere processes remain unclear. Using the pot experiments and multi-omics analyses, this study examined how low (75 mg/kg) and high (150 mg/kg) Zn application rates influence wheat Cd accumulation. Low Zn application reduced grain Cd content by 38.7% and total plant Cd accumulation by 25.0%, along with a 5.2% decrease in DTPA-extractable Cd concentration in rhizosphere soil. Metabolomic and 16S rRNA sequencing showed that low Zn application decreased several key organic and amino acids and enriched Cd-immobilizing bacteria (Azospirillum and Rhodobacter), thereby reducing Cd bioavailability in the rhizosphere. Spearman correlation analysis indicated that low Zn application regulated the abundance of Cd-related bacteria by altering specific organic acids in the wheat rhizosphere. In contrast, high Zn application increased Cd accumulation, raising rhizosphere DTPA-extractable Cd concentration by 22.6%, likely because excessive Zn transformed iron-manganese oxide-Cd into exchangeable-Cd, despite reducing the abundance of rhizosphere organic and amino acids. These findings clarify distinct rhizosphere mechanisms driving Cd accumulation under varying Zn rates, providing a theoretical basis for optimizing Zn fertilization to mitigate Cd contamination in wheat production.