The potential of fulvic acid (FA) to improve plant growth has been acknowledged, but its effect on plant growth and nutrient uptake under nutrient stress remains unclear. This study investigated the effects of different FA application rates on maize growth and nitrogen utilization under low nitrogen stress. The results showed that under low nitrogen stress, FA significantly stimulated maize growth, particularly root development, biomass, and nitrogen content. The enhanced activity levels of key enzymes in nitrogen metabolism were observed, along with differential gene expression in maize, which enriched nitrogen metabolism, amino acid metabolism and plant hormone metabolism. The application of FA regulated the hormones' level, reduced abscisic acid content in leaves and Me-JA content in roots, and increased auxin and zeatin ribose content in leaves. This study concludes that, by promoting root development, nitrogen metabolism, and hormone metabolism, an appropriate concentration of FA can enhance plant tolerance to low nitrogen conditions and improve nitrogen use efficiency.
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