Abstract
This study aimed to reveal the bacterial community and fermentation quality of Leymus chinensis silage during the fermentation process. L. chinensis was harvested at the heading stage, and ensiled with lactic acid bacteria (LAB, L), water (W), or a combination of both (LW) in vacuum-sealed plastic bags. As a control silage, untreated L. chinensis silage was also assessed. The samples were taken at 0, 5, 15, 35, and 60 days after ensiling. The bacterial community structure was assessed by plate cultivation and Illumina sequencing, and the fermentation parameters were also analyzed. Fresh L. chinensis contained low moisture (509 g/kg) and LAB (3.64 log colony-forming units/g fresh weight). Control silage displayed higher pH and lower lactic acid (LA) than other treatments during ensilage (p < 0.05); moreover, LW-treatment had lower pH from 5 to 35 days and greater LA at 5 days than L- and W-treatments (p < 0.05). During the fermentation process, Lactobacillus in L- and LW-treatments was the most dominant bacterial genus (>97%), had higher abundance than that in control silage and W-treatment (p < 0.05), and correlated negatively with other main genera and pH, and positively with LA and acetic acid (p < 0.05). Moreover, Lactobacillus had considerable abundance in W-treatment from 5 to 15 days (81.38–85.86%). Enterobacteriaceae had the most abundance among bacteria in control silage during ensiling (49.31–69.34%), and in W-treatment from 35 to 60 days (47.49–54.15%). The L-, W-, and LW-treatments displayed the aggregated bacterial community at 5 and 15 days, with W-treatment diverging from L- and LW-treatments at 35 and 60 days. Overall, the low moisture and/or insufficient LAB in fresh L. chinensis led to Enterobacteriaceae dominating bacterial community and contributing to the high pH and low LA in control silage during the fermentation process. Applying L, W, or LW contributed to Lactobacillus succession, LA production, and pH reduction during early stage of fermentation; moreover, treating with L and LW displayed more efficiency. Lactobacillus dominated the entire ensilage process in L- and LW-treatments and the early stage of fermentation in W-treatment, and contributed to the satisfactory fermentation quality of L. chinensis silage. The L- and LW-treatments displayed a similar pattern of bacterial succession during ensiling.
Highlights
Leymus chinensis is a native cool-season perennial grass of the Poaceae family, and is widely distributed throughout temperate northern Asia (Zhang and Yu, 2017)
Some studies have reported that the insufficient count of epiphytic lactic acid bacteria (LAB) in fresh L. chinensis contributes to high pH (5.63 and 4.31) and low lactic acid (LA, 12.5 and 17.64 g/kg dry matter (DM)) of silage (Zhang et al, 2015a, 2016)
The fresh L. chinensis contained low moisture content (509 g/kg) and LAB count (3.64 log colony-forming units (CFU)/g fresh weight (FW)) (Figures 1, 2), which contributed to high pH (5.93) and coliform count (5.45 log CFU/g FW), and low LA and acetic acid (AA) concentrations (2.32 and 6.23 g/kg DM, respectively) in control silage (Figure 1)
Summary
Leymus chinensis is a native cool-season perennial grass of the Poaceae family, and is widely distributed throughout temperate northern Asia (Zhang and Yu, 2017). It is a major forage resource for herbivores in meadow and typical steppes in Inner Mongolia, Northern China, due to its high yield, high protein content, and good palatability (Zhang et al, 2016). Tian et al (2014), Xue et al (2017), and Zhang and Yu (2017) have suggested that hetero-fermentative LAB dominates the fermentation process of L. chinensis silage in the absence of specific inoculation, owing to the relatively low ratio of LA and acetic acid (AA) in the silage. The microbial communities present in L. chinensis silage are not comprehensively characterized, but understanding them is critical to explaining the unique fermentation quality of its silage
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