Brown sugar levels influence fermentation quality and microbiota of mixed wheat straw and Pennisetum giganteum silage

This study investigated the effects of different levels of brown sugar addition on the fermentation quality and microbial community structure of mixed wheat straw and Pennisetum giganteum silage, aiming to provide a theoretical basis for optimizing ensiling techniques for Pennisetum giganteum . In this experiment, fresh Pennisetum giganteum and wheat straw were used as ensiling materials at a 7:3 fresh-weight ratio ( Pennisetum giganteum : wheat straw)were used as ensiling materials. A composite microbial inoculant, consisting of Lactiplantibacillus plantarum (≥ 1 × 10 11 CFU/g), Lentilactobacillus buchneri (≥ 2 × 10 10 CFU/g), and cellulase (≥ 1 × 10 4 U/g), was added to all treatment groups at a uniform rate of 0.01 g kg −1 fresh weight. Five treatment groups were then established with brown sugar addition levels of 0 (T0), 2 (T2), 4 (T4), 6 (T6) and 8 (T8) g kg −1 fresh weight, respectively, with three replicates per group. The silage was fermented at room temperature for 60 days. The results showed that: (1) The contents of acetic acid ( P < 0.05)and lactic acid ( P < 0.01) in group T6 were significantly or highly significantly higher than those in the other groups; the butyric acid contents in groups T6 and T8 were significantly lower than those in T0 and T2 ( P < 0.05). (2) PCoA and NMDS analyses revealed a clear separation between the T0 and T6 groups, indicating that brown sugar addition significantly altered the overall microbial community structure of the silage. (3) Network structure analysis results show that the addition of brown sugar altered the network characteristics of the silage bacterial community, with the highest average degree and graph density observed in groups T4 and T6, indicating enhanced cooperativity among genera. In conclusion, the addition of an appropriate amount of brown sugar effectively improved the fermentation quality and optimized the microbial community structure of mixed wheat straw and Pennisetum giganteum silage, with the best fermentation outcome observed at a brown sugar addition level of 6 g kg −1 .