Non-targeted metabolomics analysis of tobacco (Nicotiana tabacum L.) roots under different soil bulk densities

Investigating the response of tobacco (Nicotiana tabacum L .) roots to different soil bulk densities and their impact on metabolites might improve leaf quality and expand the range of tobacco's applications. In this study, a pot experiment was conducted using flue-cured tobacco as the experimental subjects under natural conditions. Soil bulk density (SBD) was manipulated by incorporating pumice or applying pressure, resulting in five distinct treatments (T1, 0.5 g·cm⁻³; T2, 0.8 g·cm⁻³; T3, 1.1 g·cm⁻³; T4, 1.4 g·cm⁻³; T5, 1.7 g·cm⁻³). The study's main approach was to use non-targeted metabolomics to analyze how the metabolites in tobacco roots are affected by varying soil bulk densities. A total of 14,594 metabolites were identified in root extracts using ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS). Differential expression was identified in 281 metabolites across the various soil bulk density treatments. Notably, nicotine was present alongside organic acids and derivatives, amino acids and derivatives, nucleotides and derivatives, sugars/alcohols, amides, and phenolic compounds. Changes in soil bulk density have an important effect on root metabolism. Root metabolites were significantly reduced in soils with SBDs either lower or higher than 1.1 g·cm −3 . High bulk density of soil caused plant root stress, increasing linoleic acid and alpha-linolenic acid levels, augmenting the ability of plant to withstand stress, and improving the production of defensive substances. These findings indicate that root metabolites can be regulated by adjusting soil bulk density, offering a new strategy to enhance tobacco quality and a unique approach to its multipurpose development as a bioreactor. • 1.Non-targeted metabolomics identifies 14,594 root metabolites. • 2.281 metabolites show differential expression across five SBDs. • 3.Nicotine and organic/amino acids altered by SBD variations. • 4.Adjusting SBD regulates root metabolites to enhance tobacco quality.