Integrated physiological and transcriptomic analysis uncovers the mechanism of moderate nitrogen application on promoting the growth and (-)-borneol accumulation of Blumea balsamifera

The results indicated that both the N1 and N2 treatments significantly promoted the growth of <i>B. balsamifera</i>, with the 150 kg N ha^-1 treatment (N1) resulting in the most favorable effects. Under the N1 treatment, the leaves harvested in October, November, and December exhibited the highest accumulation of (-)-borneol, with yields of 782 mg plant^-1, 1102 mg plant^-1, and 1774 mg plant^-1, respectively, which were significantly different from those observed in the CK and N2 treatments. Comparative transcriptome analysis revealed a total of 6,714 differentially expressed genes (DEGs). Notably, several DEGs associated with auxin signaling and N metabolism were upregulated in the N1 and N2 treatments. In contrast, many DEGs related to carbohydrate metabolism, terpenoid backbone biosynthesis, monoterpenoid biosynthesis, and flavonoid biosynthesis were significantly upregulated in the CK treatment. Moreover, potential transcription factors (TFs) that may link N nutrition with the synthesis of medicinal components were identified. Our study demonstrates that N can enhance the accumulation of (-)-borneol in <i>B. balsamifera</i> when applied in appropriate quantities. These findings provide a comprehensive understanding of the relationship between N nutrition and (-)-borneol yield in <i>B. balsamifera</i>, offering valuable insights for future cultivation practices.