Kai Cai

Introduction: Small molecule metabolites can act as soil conditioners to improve the soil environment and thereby promote crop growth. Like many other components of root exudates, succinic acid not only contributes to plant growth and stress resistance but also influences microbial growth in soil, thereby participating in the carbon cycle. Succinic acid is believed to act as a signaling molecule that bridges the host plant and microorganisms during their interactions. However, the mechanism by which succinic acid affects microbes, metabolites and their interaction in soil remains unclear.Methods: High-throughput sequencing and pseudotargeted metabolomics techniques were applied for exploring the effects of succinic acid in tobacco-planting soil and corresponding tobacco chemical composition.Results: The addition of succinic acid improved the soil chemical properties for increasing the available potassium, total nitrogen, total phosphorus and total potassium, and had a positive impact on soil fertility. In the microbial communities, fungi were more sensitive to succinic acid than bacteria. The relative abundance of Proteobacteria in the bacterial community was significantly decreased, while that of Chloroflexi was significantly increased. The relative abundances of Actinobacteriota and Acidobacteriota also showed a decreasing trend. The relative abundances of Ascomycota and Basidiomycota in the fungal community increased significantly, while the relative abundance of Chytridiomycota decreased significantly. The microbial function prediction indicated that 0.4% succinic acid may affected the nutrients and carbon-nitrogen cycles. In the soil metabolomics, the absolute contents of monosaccharide, disaccharide, sugar alcohol and trehalose in soil metabolites increased significantly. The 47 characteristic metabolites were significantly enriched in amino acid metabolism and carbohydrate metabolism. Correlation analysis showed that soil microbes were mainly positively correlated with amino acids and sugars. In addition, the relative abundances of monosaccharide, disaccharide and sugar alcohol increased in tobacco leaf, while alkaloid and amino acid decreased for improving the tobacco chemical composition.Conclusion: This study demonstrated that the addition of succinic acid affected soil chemical property, microbial communities and the composition of soil metabolites, and then improved crop chemical components.

Soil metabolites are not only the integrated expression of soil biological activities but also the pivotal drivers of biogeochemical cycling, thereby significantly influencing the formation of crop quality. This study established an improved ultra‐performance liquid chromatography (UPLC) fingerprint with chemometrics for characterizing the nonvolatile metabolite profiles of soils from geographical locations defined by different tobacco flavor styles in Guizhou. The homogenization extraction and then UPLC analysis were selected as the optimal system due to their superior repeatability and reproducibility, with intraday and interday RSD% of the common peaks (retention time and peak area) below 2.75%. The fingerprint profiling was established using 18 soil samples from three locations, namely the honey‐sweet region I, II, and the fresh‐sweet region. Thirty common peaks were identified, with similarities ranging from 0.809 to 0.956. Then, the common peaks were subjected to chemometrics analysis. These results indicated that significant differences were observed by principal component analysis (PCA), and 17 characteristic metabolites were viewed as primarily discriminatory by partial least squares discriminant analysis (PLS‐DA). The total content of characteristic metabolites followed a trend of honey‐sweet region II > honey‐sweet region I > fresh‐sweet region, with individual metabolites generally higher in the honey‐sweet region. Finally, external validation using the hierarchical cluster analysis (HCA) and Fisher discriminant analysis (FDA) model accurately classified four soil samples, further confirming the representativeness of the characteristic metabolites. This study supplies a theoretical foundation to understand the relationship between tobacco flavor formation and soil metabolism, showing great potential applications in agricultural research.

Whether nitrogen (N)-metabolic versatility is a common trait of N-transforming microbes or if it only occurs in a few species is still unknown. We collected 83 soil samples from six soil types across China, retrieved 19 publicly available metagenomic marine sample data, and analyzed the functional traits of N-transforming microorganisms using metagenomic sequencing. More than 38% and 35% of N-transforming species in soil and marine ecosystems, respectively, encoded two or more N-pathways, although N-transforming species differed greatly between them. Furthermore, in both soil and marine ecosystems, more than 80% of nitrifying and N-fixing microorganisms at the species level were N-metabolic versatile. This study reveals that N-metabolic versatility is a common trait of N-transforming microbes, which could expand our understanding of the functional traits of drivers of nitrogen biogeochemistry.

2, 6-diisopropylaniline (2, 6-DIPA) is a crucial non-intentionally organic additive that allows the assessment of the production processes, formulation qualities, and performance variations in biodegradable mulching film. Moreover, its release into the environment may have certain effects on human health. Hence, this study developed simultaneous heating hydrolysis–extraction and amine switchable hydrophilic solvent vortex-assisted homogeneous liquid–liquid microextraction for the gas chromatography–mass spectrometry analysis of the 2, 6-DIPA additive and its corresponding isocyanates in poly(butylene adipate-co-terephthalate) (PBAT) biodegradable agricultural mulching films. The heating hydrolysis–extraction conditions and factors influencing the efficiency of homogeneous liquid–liquid microextraction, such as the type and volume of amine, homogeneous-phase and phase separation transition pH, and extraction time were investigated and optimized. The optimum heating hydrolysis–extraction conditions were found to be a H₂SO₄ concentration of 2.5 M, heating temperature of 87.8 °C, and hydrolysis–extraction time of 3.0 h. As a switchable hydrophilic solvent, dipropylamine does not require a dispersant. Vortex assistance is helpful to speed up the extraction. Under the optimum experimental conditions, this method exhibits a better linearity (0.0144~7.200 μg mL⁻¹ with R = 0.9986), low limit of detection and quantification (0.0033 μg g⁻¹ and 0.0103 μg g⁻¹), high extraction recovery (92.5~105.4%), desirable intra- and inter-day precision (relative standard deviation less than 4.1% and 4.7%), and high enrichment factor (90.9). Finally, this method was successfully applied to detect the content of the additive 2, 6-DIPA in PBAT biodegradable agricultural mulching films, thus facilitating production process monitoring or safety assessments.

The quality of crops is closely associated with their geographical location and yield, which is reflected in the composition of their metabolites. Hence, we employed GC–MS pseudotargeted metabolomics to investigate the metabolic characteristics of high-, medium-, and low-yield Nicotiana tabacum (tobacco) leaves from the Bozhou (sweet honey flavour) and Shuicheng (light flavour) regions of Guizhou Province. A total of 124 metabolites were identified and classified into 22 chemical categories. Principal component analysis revealed that the geographical location exerted a greater influence on the metabolic profiling than the yield. Light-flavoured tobacco exhibited increased levels of sugar metabolism- and glycolysis-related intermediate products (trehalose, glucose-6-phosphate, and fructose-6-phosphate) and a few amino acids (proline and leucine), while sweet honey-flavoured tobacco exhibited increases in the tricarboxylic acid cycle (TCA cycle) and the phenylpropane metabolic pathway (p-hydroxybenzoic acid, caffeic acid, and maleic acid). Additionally, metabolite pathway enrichment analysis conducted at different yields and showed that both Shuicheng and Bozhou exhibited changes in six pathways and four of them were the same, mainly C/N metabolism. Metabolic pathway analysis revealed higher levels of intermediates related to glycolysis and sugar, amino acid, and alkaloid metabolism in the high-yield samples, while higher levels of phenylpropane in the low-yield samples. This study demonstrated that GC–MS pseudotargeted metabolomics-based metabolic profiling can be used to effectively discriminate tobacco leaves from different geographical locations and yields, thus facilitating a better understanding of the relationship between metabolites, yield, and geographical location. Consequently, metabolic profiles can serve as valuable indicators for characterizing tobacco yield and geographical location.