Non-Targeted Metabolomics Reveals Tobacco Metabolites Associated with Roasted Tobacco Quality Under Organic Substitution

The present study investigated the effect of the replacement of chemical fertilizers by organic fertilizers on agronomic traits of tobacco at maturity as well as on the conventional chemical quality of post-roasted tobacco leaves. To better understand the relationship between tobacco metabolites and roasted tobacco under organic nitrogen replacement treatments, post-roasting tobacco leaves were analyzed by an untargeted metabolomics analytical approach to identify key metabolites applicable to predicting tobacco quality. Methods: Yunyun Tobacco 87 was adopted as the test material in a field plot experiment with five fertilization treatments: T1 (100% chemical nitrogen fertilizer), T2 (25% organic nitrogen fertilizer + 75% chemical nitrogen fertilizer), T3 (50% organic nitrogen fertilizer + 50% chemical nitrogen fertilizer), T4 (75% organic nitrogen fertilizer + 25% chemical nitrogen fertilizer), and T5 (100% organic nitrogen fertilizer). Additionally, the non-targeted metabolomics approach was employed for the in-depth analysis of metabolites in roasted tobacco leaves. Results: The targeted metabolomic analysis identified 991 metabolites in the positive ion pattern and 673 in the negative ion pattern across all treatments. Among these, certain pathways such as alanine, aspartate, and glutamate metabolism, D-amino acid metabolism, purine metabolism, tryptophan metabolism, and galactose metabolism were up-regulated, whereas other pathways such as starch and sucrose metabolism, betalain biosynthesis, and biosynthesis of unsaturated fatty acids were down-regulated and significantly enriched with differential metabolites. This study revealed the significant differences in the metabolite composition under different fertilization conditions, with a strong correlation between metabolites and tobacco quality indices. Organic fertilizers were observed to enhance tobacco quality by influencing tobacco metabolism, providing a scientific basis for optimizing fertilization strategies and improving tobacco quality.