Key points are not available for this paper at this time.
Water activity (Aw) is a critical factor in solid-state fermentation, as only free water supports nutrient dissolution and microbial metabolism. In ensiling, which is an anaerobic solid-state fermentation of plant materials, Aw strongly influences microbial activity and fermentation outcomes. However, systematic investigations on Aw in paper mulberry (Broussonetia papyrifera) remain limited. Variations in fermentation quality may be more closely associated with differences in Aw levels. This study investigated three Aw levels (0.989, 0.971, and 0.961) across five ensiling periods (0, 3, 7, 14, and 45 days) to assess their effects on fermentation quality, microbial community dynamics, and metabolic functions using absolute quantitative sequencing and Biolog-Eco plates. The medium Aw level (0.971) yielded the most favorable fermentation outcomes, characterized by the lowest pH (4.66) and ammoniacal nitrogen content (19.16 g kg⁻¹ TN). Notably, group differences diminished after 14 days. Microbial communities exhibited divergence in the early stages but converged over time, with Weissella predominating overall, while Pediococcus and Lactiplantibacillus became prominent under low Aw conditions. Biolog-Eco analysis indicated that reduced Aw led to decreased metabolic diversity, peaking at day 14. Conversely, high Aw levels enhanced carbon source utilization, particularly by Lactococcus and Levilactobacillus. In conclusion, Aw plays a significant role in regulating microbial succession and metabolism in paper mulberry silage. Maintaining a medium to high Aw range (0.971–0.989) promotes lactic acid bacteria-dominated fermentation, thereby enhancing fermentation stability and improving nutrient preservation efficiency.
Yang et al. (Fri,) studied this question.