Dynamic Effects of Exogenous and Epiphytic Pediococcus pentosaceus on Quality and Bacterial Community Succession of Silage Mulberry Leaves

The aim of this study is to investigate the dynamic changes in nutritional components, fermentation parameters, and microbial communities of mulberry leaves during silage fermentation with exogenous and epiphytic Pediococcus pentosaceus (P. pentosaceus). P. pentosaceus P (Pp) and P. pentosaceus M (Pm), isolated from the epiphytic microbiota of paper mulberry and mulberry leaves, respectively, were used as fermentation inoculants (OD600 = 0.6). Fresh mulberry leaves were treated with the inoculants at 1% (mL/g) of leaf weight and ensiled for 60 days. Three groups were established: T1 (exogenous Pp), T2 (epiphytic Pm), and CK (control, sterile water). Samples were collected on days 1, 3, 5, 7, 15, 30, and 60 to analyze chemical composition, fermentation characteristics, and bacterial communities. Redundancy analysis was conducted to explore relationships between fermentation characteristics and bacterial communities. The results showed that T2 had significantly higher dry matter content from day 30 (p < 0.05) and lower neutral detergent fiber content from day 3 (p < 0.05) compared to T1. Additionally, T2 exhibited faster water-soluble carbohydrate consumption and more rapid pH decline during the early fermentation phase (days 1–7). Lactic acid (LA) content in T2 was significantly higher during days 1–7 (p < 0.05), while acetic acid (AA) content was significantly lower from day 3 (p < 0.05). T2 consistently showed higher crude protein and lower ammonia nitrogen (NH3-N) levels than T1 throughout fermentation. Microbial analysis revealed higher abundance of Firmicutes in T2 during days 1–15 and greater relative abundance of Pediococcus from day 1 to 30. Kosakonia was more abundant in T2, whereas Escherichia-Shigella was less abundant. During days 3–15, bacterial communities in T1 and T2 correlated positively with LA, with stronger effects in T2, driven by Pediococcus. In the later stages (days 30 and 60), bacterial communities were influenced by AA, NH3-N, and propionic acid, with Enterobacter, Lactobacillus, and Enterococcus as key contributors. This study demonstrates that supplementing epiphytic P. pentosaceus improves fermentation efficiency and nutritional quality of mulberry leaf silage compared to exogenous P. pentosaceus.