BackgroundAlfalfa (Medicago sativa L.) is one of the most important forage resources in the world due to its high nutritive value. However, its nutritional quality decreases during the transition from budding to flowering. Previous research revealed a decreased crude protein content and increased fibre content in alfalfa forage harvested at later maturity stages, leading to a reduction in nutritional quality. However, the reasons for this phenomenon have not been explained at the molecular level.ResultsIn this study, leaves from the WL319HQ alfalfa cultivar were harvested at two developmental stages (budding and mid-flowering). The leaves were used to test the variable expression of proteins and metabolites during these stages. TMT-based quantitative proteomics and LC-MS/MS-based untargeted metabolomics methods were employed in this study. A total of 415 proteins and 49 metabolites showed at least a 1.2-fold difference in abundance during these stages. Most of the differentially expressed proteins and metabolites were involved in metabolic processes, including carbohydrate metabolism, starch and sucrose metabolism, phenylpropanoid biosynthesis, and biosynthesis of amino acids. Alfalfa leaves in mid-flowering contain less crude protein due to the decrease in L-glutamic acid content. Carbohydrate metabolism provides the raw material for the synthesis of hemicellulose, resulting in an increase in the hemicellulose content of the alfalfa leaves, leading to an increase in the NDF content. In addition, the increase in L-phenylalanine content could have provided the conditions necessary for lignin synthesis. These are the main factors leading to reductions in alfalfa relative feed value (RFV) and quality.ConclusionsThis study used joint proteomic and metabolomic analyses to elucidate the relationship between the reduction in the nutritional value of alfalfa and complex biological processes. This provides a theoretical basis for producing high-quality alfalfa hay and sets the stage for further research.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1291-8) contains supplementary material, which is available to authorized users.
This study aimed to isolate and identify lactic acid bacteria (LAB) from the native grass and naturally fermented silage from the Mongolian Plateau. The effect of selected strains on bacterial community and quality of native grass silage was also studied. Strains XM2, 265, and 842 could grow normally at 15°C–30°C, pH 4.0–8.0, and NaCl 3 and 6.5%; they were identified as Lactiplantibacillus plantarum subsp. plantarum, Pediococcus acidilactici, and Latilactobacillus graminis, by sequencing 16S rRNA, respectively. The three strains (XM2, 265, and 842) and one commercial additive (L) were used as inoculants and singularly added to the native grass. Compared to the control, the dry matter content was significantly (p < 0.05) lower in L and XM2 groups. The water-soluble carbohydrate content was significantly (p < 0.05) higher in control than in other groups. Compared with the control, the crude protein and ammonia nitrogen contents were significantly (p < 0.05) higher and lower in the LAB-treated groups, and the acid and detergent fiber contents were significantly (p < 0.05) reduced in the L and XM2 groups than those in other groups. There was a significant (p < 0.05) difference in the pH value, lactic acid content, and lactic acid-to-acetic acid ratio in L and XM2 groups than in other groups. Compared with the control, the number of LAB was significantly (p < 0.05) higher in LAB-treated silages, whereas no significant (p > 0.05) differences were observed in yeast and aerobic bacteria in all groups. Compared to the control, the Shannon index was significantly (p < 0.05) reduced. Simpson and Chao1 were significantly (p < 0.05) increased. Principal coordinate analysis based on the unweighted UniFrac distance showed clear separation of the bacterial community in fresh materials and LAB-treated silages. Besides, compared to the control, the principal coordinate analysis of LAB-treated silages was also separate. After 30 days of fermentation, the relative abundance of Firmicutes increased and was the primary phylum in all silages. Compared with the control, the abundance of Firmicutes and Proteobacteriawas significantly (p < 0.05) higher and lower in L and XM2 groups. In contrast, no significant differences were observed among control, 265, and 842 groups. At the genus level, the relative abundance of Lactobacillus, Enterobacter, Pediococcus, and Weissella was increased and dominated the native grass fermentation. Compared with the control, the abundance of Lactobacillus was significantly (p < 0.05) higher in L, XM2, and 842 groups, while no significant (p > 0.05) differences were observed between the control and 265 groups. The abundance of Pediococcus was higher than that in other groups. Consequently, the results demonstrated that LAB significantly influenced silage fermentation by reconstructing microbiota, and Lactobacillus was the dominant genus in the native grass silages. Furthermore, the results showed that strain XM2 could effectively improve the silage quality, and it is considered a potential starter for the native grass silage.
Ensiling native grass is an effective method to protect the nutritional quality of forage and alleviate feed shortages in the cold winter of the Inner Mongolian Plateau. To improve the usability of native grass resources as feed in China, the effects of lactic acid bacteria and molasses additions on the microbial population, fermentation quality, and nutritional quality of native grass during silage were investigated. Treatments were a control treatment with no additive (CK), lactic acid bacteria (L), molasses (M), and lactic acid bacteria in combination with molasses (L+M), all of which were stored at ambient temperature (17–28°C) for 7, 14, 30, and 60 days. The results showed that all additives improved nutritional value and fermentation quality with low pH and ammonia nitrogen (NH3–N) and high crude protein (CP) and water soluble carbohydrate (WSC) than control silage over the ensiling period. Compared with L or M silage, the L+M silage combination improved fermentability, as evidenced by higher LA content and a faster pH drop during the first 7 days of ensiling. With prolonged ensiling time, the combined addition of L and M could increase the count of desirable Lactobacillus, decrease microbial diversity, and inhibit the growth of undesirable microorganism, such as Clostridia, Escherichia, and Enterobacter abundance compared with silage treated with CK, L. or M. Application of L together with M could further improve the silage quality of native grass by altering bacterial community structure. In summary, the addition of lactic acid bacteria and molasses increased the relative abundance of Lactobacillus of native grass silage and improved fermentation quality.
BackgroundIt is predicted that climate change may increase the risk of local droughts, with severe consequences for agricultural practices.MethodsHere we report the influence of drought on alfalfa yields and nutritional composition, based on artificially induced drought conditions during two field experiments. Two types of alfalfa cultivars were compared, Gold Queen and Suntory. The severity and timing of drought periods were varied, and the crop was harvested either early during flowering, or late at full bloom.ResultsThe obtained dry mass yields of Gold Queen were higher than Suntory, and the first was also more resistant to drought. Early harvest resulted in higher yields. Decreases in yields due to water shortage were observed with both cultivars, and the fraction of crude protein (CP) decreased as a result of drought stress; this fraction was higher in Gold Queen than in Suntory and higher in early harvest compared to late harvest. Severe drought late in spring had the highest effect on CP content. The fraction of fibre, split up into neutral detergent fibre (NDF) and acid detergent fibre (ADF) increased as a result of drought and was lower in early compared to late harvested plants. Suntory alfalfa produced higher fibre fractions than Gold Queen. The fraction of water-soluble carbohydrates (WSC) was least affected by drought. It was consistently higher in Gold Queen compared to Suntory alfalfa, and late harvest resulted in higher WSC content.ConclusionsIn combination, these results suggest that the nutritive value of alfalfa will likely decrease after a period of drought. These effects can be partly overcome by choosing the Gold Queen cultivar over Suntory, by targeted irrigation, in particular in late spring, and by harvesting at an earlier time.Electronic supplementary materialThe online version of this article (doi: 10.1186/s12870-017-1226-9) contains supplementary material, which is available to authorized users.
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