Fermentative products and bacterial community structure of C4 forage silage in response to epiphytic microbiota from C3 forages

Abstract

Objective: The observation that temperate C₃ and tropical C₄ forage silages easily produce large amounts of ethanol or acetic acid has puzzled researchers for many years. Hence, this study aimed to assess the effects of epiphytic microbiota from C₃ forages (Italian ryegrass and oat) on fermentative products and bacterial community structure in C₄ forage (sorghum) silage.Methods: Through microbiota transplantation and γ-ray irradiation sterilization, the irradiated sorghum was treated: i) sterile distilled water (STSG); ii) epiphytic microbiota from sorghum (SGSG); iii) epiphytic microbiota from Italian ryegrass (SGIR); iv) epiphytic microbiota from oat (SGOT).Results: After 60 days, all the treated groups had high lactic acid (>63.0 g/kg dry matter [DM]) contents and low pH values (<3.70), acetic acid (<14.0 g/kg DM) and ammonia nitrogen (<80.0 g/kg total nitrogen) contents. Notably, SGIR (59.8 g/kg DM) and SGOT (77.6 g/kg DM) had significantly (p<0.05) higher ethanol concentrations than SGSG (14.2 g/kg DM) on day 60. After 60 days, <i>Lactobacillus</i> were predominant genus in three treated groups. Higher proportions of <i>Chishuiella</i> (12.9%) and <i>Chryseobacterium</i> (7.33%) were first found in silages. The ethanol contents had a positive correlation (p<0.05) with the abundances of <i>Chishuiella</i>, <i>Acinetobacter</i>, <i>Stenotrophomonas</i>, <i>Chryseobacterium</i>, and <i>Sphingobacterium</i>.Conclusion: The epiphytic bacteria on raw materials played important roles in influencing the silage fermentation products between temperate C₃ and tropical C₄ forages. The quantity and activity of hetero-fermentative <i>Lactobacillus</i>, <i>Chishuiella</i>, <i>Acinetobacter</i>, <i>Stenotrophomonas</i>, <i>Chryseobacterium</i>, and <i>Sphingobacterium</i> may be the key factors for the higher ethanol contents and DM loss in silages.