Leguminous and gramineous plant silages display unique characteristics of bacterial community ecology

Silage is the most important part of a ruminant diet and is also a renewable feedstock. Leguminous and gramineous plants are the main materials used to make silage. However, the general characteristics of silage fermentation and the mechanisms of microbial processes of Leguminosae and Gramineae have yet to be clarified. Therefore, we examined which of the following contribute to differences in silage quality between leguminous (3 genera, 29 varieties) and gramineous (4 genera, 23 varieties) plants: microbial diversity, composition, functional profile, assembly process, or molecular ecological network.

Diminished concentrations of propionic acid and butyric acid indicated that Leguminosae created silage of a superior quality compared to gramineous silage, which is further supported by the elevated V-score value. The α- and β-diversity indices showed obvious differentiation in bacteria diversity patterns between the gramineous and leguminous plant silages. The community compositions differed significantly as well. Pseudomonas dominated in gramineous silage, and Enterobacteriaceae (UG) and Lactobacillus dominated in leguminous silage. Meanwhile, the enriched Enterobacteriaceae (UG) and Lactobacillus, as well as the biomarker taxa Janthinobacterium and Pseudomonas, were designated critical silage microorganisms. In addition, the close correlation of bacterial and fermentation parameters revealed that silage quality is highly influenced by microbial composition. Additionally, leguminous and gramineous silages differed significantly in their microbial functional profiles, with many pathways significantly enriched in the gramineous silage, including biosynthesis of other secondary metabolites. Furthermore, the assembly mechanisms of the gramineous and leguminous silage microbial communities were determined by both stochastic and deterministic processes, with dispersal limitation being more influential than homogeneous selection. Moreover, the two bacterial co-occurrence networks were mainly cooperative, though the gramineous silage network was tighter and more complex than the leguminous silage network. Network module analysis showed that the diversity of modules and the bacterial composition of the largest module clearly differed between the gramineous and leguminous silage microbes. Finally, that leguminous silage had a noticeably higher robustness and an excellent natural connectivity indicates it had the more stable microbial network of the two.

This study revealed the differences between gramineous and leguminous plant silages in terms of fermentation quality, bacterial diversity, composition, functional profile, assembly mechanism and co-occurrence network. This outcome deepens our understanding of silage microbial processes across different plant families, and also provides a scientific basis from which to develop a protocol for the precise regulation of silage quality.