Transcriptomic and metabolomic analysis of tobacco responses to combined organic-chemical fertilization

The combined application of organic fertilizer and chemical fertilizer can affect plant physiological activities and change the expression of its related genes and metabolites. However, past studies mainly focused on the effects of the combined application of organic and inorganic fertilizers on soil physical and chemical properties, microbial communities, and crop physiological changes, but the response mechanism of plant leaf metabolic cycles to different combined applications of organic fertilizers is not yet completely clear. Therefore, this study employed tobacco as a model crop to investigate the intrinsic regulatory mechanisms of physiological metabolism in tobacco leaves following the combined application of three distinct organic materials with chemical fertilizer and cattle manure. The research first revealed that the composite application of chemical fertilizer, cattle manure, and high-carbon-based compost (CMHC) exerted the most pronounced stimulatory effect on the growth and development of tobacco glandular trichomes. Compared to the control group (CK) treated solely with chemical fertilizer, glandular trichome density increased by 1.56-fold, while α-cembratriene diol and β-cembratriene diol content rose significantly by 146.40% and 2.39-fold respectively. This study employs transcriptomic and metabolomic analyses to reveal for the first time the molecular mechanism by which the combined application of cattle manure with other organic fertilizers enhances tobacco leaf defense capacity. This is achieved by regulating key genes, such as phosphoethanolamine N-methyltransferase and nicotine N-demethylase, in the glycerophospholipid metabolism as well as the tropane, piperidine, and pyridine alkaloid biosynthesis pathways. These regulatory actions promote the synthesis of downstream resistance substances, including N-methyldiethanolamine and nicotine. Notably, in the treatment combining cattle manure with humic acid (CMHC), the upregulation of genes such as glutamate-oxaloacetate transaminase and nicotinate reductase I modulates energy metabolism shifts in the leaves, thereby synergistically promoting leaf growth and the secretion of glandular trichome exudates. In summary, this study systematically elucidates the molecular mechanisms by which the combined application of organic fertilizer regulates tobacco leaf development and metabolite synthesis from an integrated transcriptomic and metabolomic perspective, providing a theoretical basis for green fertilisation and quality improvement in tobacco cultivation.