Sustainable production of selenium-rich and cadmium-safe rice by nZVI–melatonin synergy via coordinated plant–microbe regulation

Abstract

Developing environmental regulation strategies to reduce cadmium (Cd) accumulation in rice while promoting selenium (Se) enrichment is crucial for global food safety and remains a significant challenge. Here, we evaluated a stage-specific co-application approach involving nanoscale zero-valent iron (nZVI) amendment to soil and foliar spraying of melatonin (MT), which decreased grain Cd concentrations by up to 64% while elevating grain Se content by up to 74% in pot experiments. It also enhanced the Se bioconcentration factor (≈63%) and the leaf-to-grain translocation factor (≈77%), indicating improved uptake and redistribution under Cd stress. Mechanistic analyses revealed synergistic metabolic reprogramming: antioxidant defenses were strengthened by elevated ascorbate peroxidase activity, which reduced hydrogen peroxide and restored redox homeostasis. Transcriptomic profiling revealed suppression of Cd influx transporters and activation of genes involved in vacuolar sequestration, antioxidant metabolism, and Se transport, thereby restricting Cd translocation while promoting Se accumulation. Rhizosphere microbiomes were enriched with beneficial taxa, including Pseudomonadota, Acidobacteriota, and Bacillota, which contributed to Cd stabilization and Se bioavailability. This nZVI–MT combined strategy offers a viable strategy for producing safe and nutritious rice.