Foliar application of ferroferric oxide nanomaterials enhance source-sink communication and growth in soybean

Innovative technology to address iron deficiency in agriculture while reducing environmental burden is needed because of increasing food demand for the rapidly rising global population. The impact of foliar application of ferroferric oxide nanomaterials (Fe₃O₄ NMs) at different concentrations (1-50 mg/L) on soybean growth were investigated in the whole life cycle. The beneficial effects of Fe₃O₄ NMs on soybean were concentration-dependent and exhibited nano-effect. Foliar application with 10 mg/L Fe₃O₄ NMs exhibited the best performance, notably improving fresh shoot biomass by 9.7-36.2 % among three stages, and increasing root/shoot ratio by 39.1-78.2 %, which are higher than commercial iron fertilizer. Transcriptomic and metabolomic analyses revealed that Fe₃O₄ NMs: (1) increased soybean photosynthesis to supply more sucrose in soybean leaves; (2) upregulated sucrose transporter genes expression, enhanced auxin and abscisic acid content, and augmented stage-specific sucrose-related metabolites (including tricarboxylic acid cycle and amino acids at seedling stage, the antioxidants at flowering and mature stage) in leaves, thereby enhancing the ability of sucrose transport from source to sink, and finally improving the developments of soybean different sinks among different stages. Our findings highlight the considerable potential of Fe₃O₄ NMs as a sustainable and high-efficiency crop fertilizer strategy.