Lactic acid bacteria metabolism affects the composition of volatile organic compounds (VOCs) in alfalfa silage, which results in differences of odor and quality. The aim of this study was to reveal the effects of commercial Lactobacillus plantarum (CL), screened Lactobacillus plantarum (LP), and screened Pediococcus pentosaceus (PP) on quality, microbial community, and VOCs of alfalfa silage based on volatile metabolomics and metagenomics. The results showed that the LP and PP groups had higher sensory and quality grades, and the dominant bacteria were Lactiplantibacillus plantarum and Pediococcus pentosaceus. The main VOCs in alfalfa silage were terpenoids (25.29%), esters (17.08%), and heterocyclic compounds (14.43%), and esters such as methyl benzoate, ethyl benzoate, and ethyl salicylate were significantly increased in the LP and PP groups (P < 0.05). Correlation analysis showed that terpenoids, esters, and alcohols with aromatic odors were positively correlated with Lactiplantibacillus plantarum and Pediococcus pentosaceus. Microbial functions in carbohydrate and amino acid metabolism, biosynthesis of secondary metabolites, and degradation of aromatic compounds were significantly enriched. In conclusion, the addition of lactic acid bacteria can increase the aromatic substances in silage and further improve silage odor and quality.

The aim of this study was to evaluate the effects of cellulase (CE) and lactic acid bacteria (LAB) on Caragana korshinskii silage by analyzing the fermentation parameters, chemical composition, and bacterial community. The Caragana korshinskii was harvested at the fruiting period and treated with cellulase and LAB alone as a control treatment with no additive (CK). The ensiling performance and bacterial community were determined after 3, 7, 15, 30, and 60 days of fermentation process. Compared with the CK group, the pH, dry matter loss, and ammonia nitrogen content were significantly (p < 0.05) decreased in the LAB and CE treatments. Compared with the CK and LAB group, the contents of acid detergent fiber, neutral detergent fiber, and acid detergent lignin in the CE group decreased significantly (p < 0.05), and the water-soluble carbohydrates, acetic acid, and lactic acid concentrations increased significantly (p < 0.05). At the genus level of microorganisms, the addition of cellulase and LAB significantly reduced the microbial diversity. Compared with the CK group (78.05%), the relative abundance of Lactiplantibacillus in the CE group (90.19%) and LAB group (88.40%) significantly (p < 0.05) increased. The relative abundance of Pediococcus in the CE group (3.66%) and LAB group (2.14%) was significantly (p < 0.05) lower than that in the CK group (14.73%). Predicted functional profiling of 16S rRNA genes revealed that the addition of cellulase and LAB increased the pyruvate metabolic pathway during Caragana korshinskii silage, thereby increasing the accumulation of lactic acid concentration. The addition of cellulase expressed a better advantage in the biosynthetic capacity of lysine. In summary, the addition of cellulase and LAB could adjust the bacterial community to improve the silage quality of Caragana korshinskii, and the addition of cellulase exhibited better results than the LAB additives.

Better quality and odor of silage and normal microbial fermentation metabolism are mostly dependent on an appropriate moisture content. The purpose of this study was to determine the effects of different moisture content gradients (50, 60, 70, and 80%) on the bacterial community, odor, and quality of alfalfa silage at 60 days by using gas chromatography–mass spectrometry (GC–MS) and electronic nose, with six replicates per group. The results showed that there were significant differences in odor response intensity among all groups, among which the 80% group had the strongest reaction to terpenoids, sulfides, and nitrogen oxides. Similarly, the different volatile organic compounds (VOCs) were mainly terpenoids, alcohols, and ketones, such as pine, camphor, and menthol (e.g., carlin and levomenthol). The dominant bacterium was Enterococcus with higher fiber, pH, and ammonia nitrogen (NH₃-N) content but poorer quality and odor (p < 0.05). The differential VOCs in the 60% group were mainly heterocyclics, esters, and phenols with fruity, floral, and sweet odors such as 2-butylthiophene and acorone. Pediococcus and Lactiplantibacillus were the dominant bacteria, with higher crude protein (CP), water-soluble carbohydrates (WSC), and lactic acid (LA) contents, as well as better quality and odor (p < 0.05). The biosynthesis of terpenoids and steroids, biosynthesis of secondary metabolites, and biosynthesis of phenylpropanoids were the main metabolic pathways of differential VOCs. In conclusion, regulating moisture content can alter bacterial community and metabolites, which will encourage fermentation and enhance alfalfa silage quality and odor.

During aerobic exposure of silage, the fatty acid and amino acid composition may alter the quality and palatability, resulting in economic losses in livestock production. The objective of this study was to evaluate the effects of Lactiplantibacillus plantarum (LP), Lenti Lentilactobacillus buchneri (LB), and a mixture of LP and LB (PB) on the fatty acids, amino acids, and antioxidant capacity of Leymus chinensis silage during aerobic exposure. The lactic acid bacteria were added at 1 × 10⁶ CFU/g. The silage treatments were opened after 60 days of fermentation, and sampled on days 0, 4, and 8 of aerobic exposure. The LB group had higher total fatty acid and polyunsaturated fatty acid content, and less decrease in amino acid content and antioxidant capacity, while the LP group had a higher monounsaturated fatty acid content but a larger decrease in all indicators after exposure. Correlation analysis showed that Lactobacillus, Cryptococcus, Penicillium, and Thermoascus were more correlated with fatty acid changes, and that Lactobacillus, Actinomyces, Clostridium, and Penicillium were more correlated with amino acid changes. In conclusion, Lentilactobacillus buchneri could effectively improve the antioxidant capacity and fatty acid and amino acid contents of Leymus chinensis silage during aerobic exposure, while Lactiplantibacillus plantarum could effectively improve the content of each index of Leymus chinensis silage at opening, but deterioration was faster during aerobic exposure.

Nanoselenium shows potential trends in improving plant health and food quality. In this study, different concentrations of nanoselenium were sprayed on the leaves of alfalfa. Compared to the control, nanoselenium (100 mg·L^-1) significantly increased SeMet and SeMeCys contents in the roots, stems, and leaves of alfalfa. Nanoselenium educed malondialdehyde by modulating the glutamine synthetase-glutamate synthetase (GS-GOGAT) cycle and activating antioxidant enzymes, including the ascorbate-glutathione (AsA-GSH) cycle, as well as enhancing photosynthesis, resulting in an increase in the alfalfa yield, crude protein, and relative feeding value. The biofortification of nanoselenium mainly changed the community structure of phyllosphere bacteria by regulating metabolic pathways such as amino acid metabolism, carbohydrate metabolism, and membrane transport, among which Proteobacteria were more responsive to nanoselenium. In conclusion, nanoselenium will enhance photosynthesis, improve signaling molecules, and recruit beneficial bacteria to regulate the nutritional levels of alfalfa.