Gamma-ray irradiation and microbiota transplantation to separate the effects of chemical and microbial diurnal variations on the fermentation characteristics and bacterial community of Napier grass silage.

Abstract

To investigate the contributions of chemical and microbial diurnal variations in fermentation characteristics and bacterial community of Napier grass silage, gamma-ray irradiated Napier grass harvested at 07.00 h (AM), 12.00 h (M) and 17.00 h (PM) was inoculated with the microbiota derived from Napier grass harvested at AM, M and PM in a 3 (irradiated forage: AMG , MG and PMG ) × 3 (microbiota: AMM , MM and PMM ) design and then ensiled for 14 and 60 days. Napier grass harvested at various times had different chemical compositions and epiphytic microbiota prior to ensiling. For silages inoculated with the same microbiota, the pH values, residual water soluble carbohydrates and dry matter contents increased, and lactic acid, acetic acid, propionic acid, butyric acid, ethanol and volatile fatty acids contents decreased in PMG and MG silages compared to AMG silages. MM and PMM inoculum promoted lactic acid fermentation as indicated by higher lactic acid contents and lactic/acetic acid ratios in MM and PMM -inculated silages compared to those in AMM -inoculated silages after 60 days of ensiling. During ensiling, epiphytic microbiota affected the Chao1 index, operational taxonomic units (OTUs) number and Shannon index, as well as the abundances, of more than half of the top 10 abundant genera, whereas chemical composition did not affect any of the bacterial diversity and richness indices and only showed significant impacts on the abundances of two genera. The results indicated that chemical diurnal variation exerted an influence mainly on the extent of fermentation, whereas microbial diurnal variation affected more the bacterial community and fermentation types during Napier grass ensiling. © 2022 Society of Chemical Industry.