Tea Tree Essential Oil Enriches Lactic Acid Bacteria and Improves Paper Mulberry Silage Quality

Paper mulberry (Broussonetia papyrifera) is a high-protein forage, but its high buffering capacity and low water-soluble carbohydrate (WSC) content hinder silage fermentation. This study evaluated the effect of tea tree (Melaleuca alternifolia) essential oil (TTO) as a natural additive for paper mulberry silage. TTO was added at 0 (CK), 500 (CSD), and 1000 mg/kg (CSG) fresh weight, with samples collected on days 7, 15, 30, and 90. After 90 days, CSD had the lowest pH and the highest lactic acid content. NH3-N/TN was significantly lower than in CK (p < 0.05), and the retention of dry matter, crude protein and water-soluble carbohydrate was improved (p < 0.05). Compared with CK, CSD exhibited the highest lactic acid bacteria (LAB) counts, along with the lowest mold and aerobic bacterial counts (p < 0.05). However, CSG did not further improve fermentation quality, and most of the indicators were not significantly different from CSD (p > 0.05). The in vitro gas production test showed that CSD significantly increased the theoretical maximum gas production and the maximum gas production rate (p < 0.05). Additionally, 16S rRNA sequencing revealed a distinct bacterial succession in CSD, which enriched beneficial lactic acid bacteria (LAB) such as Pediococcus while outcompeting less competitive taxa. This microbial reshaping redirected the community toward acidification and nutrient retention. Collectively, these results demonstrate that TTO at 500 mg/kg is a promising natural additive for improving paper mulberry silage quality through selective reshaping of the bacterial community.