Responses of microbial community dynamics, co-occurrences, functional shifts, and natural fermentation profiles of Elymus nutans silage to altitudinal gradients

Abstract

ABSTRACT This study investigated the microbial diversity, functionality, and fermentation quality of Elymus nutans ( E. nutans ) silage across different altitudinal gradients. Forage samples were gathered from three areas in Qinghai province, China, namely, Huangyuan (HY, altitude of 2,613 m); Xinghai (XH, altitude of 3,612 m), and Chenduo (CD, altitude of 4,589 m) counties. Chopped E. nutans were ensiled at local room temperature and sampled after 7, 14, 30, and 60 days of ensiling. The results exhibited that the bacterial diversity and numbers of the lactic acid bacteria (LAB) and yeast in E. nutans forage decreased, while the water-soluble carbohydrates and crude protein increased along the altitudinal gradients. This led to clear differences in fermentation qualities and bacterial community dynamics. The silage from CD with high altitude showed a higher fermentation quality, more stable bacterial network structure, and lower abundance of amino acid metabolism than ensiled forages collected from the other regions ( P < 0.05). Meanwhile, the LAB including Lacticaseibacillus and Levilactobacillus were identified as differentially abundant taxa in silage sample from CD after 60 days of ensiling; in contrast, the undesirable microbiota were still the differentially abundant taxa in the silages from HY and XH. Correlation analysis further confirmed that altitude affects the epiphytic microbial structure and nutrition distribution of E. nutans forage, leading to varying levels of fermentation. Considering the complex microbial composition of fresh forage, LAB inoculation is highly suggested for E. nutans silage making in the Qinghai regions with low altitudes. IMPORTANCE On the Qinghai-Tibet Plateau (QTP), feed shortages are common due to cold environmental conditions and the short growing season of crops. Therefore, effective preservation, such as the ensiling of local forage, is becoming increasingly important to balance the seasonal imbalance between the forage supply and the nutritional needs of domestic animals in this area. However, the structure of the microbial community of the forage, which is influenced by climatic conditions such as altitude differences, has a major impact on the fermentation quality and microbial succession of the ensiled forage. Therefore, we investigated microbial community dynamics, co-occurrence, functional shifts, and natural fermentation profiles of Elymus nutans silage as a function of altitudinal gradients. Results show that silage from Chenduo at higher elevations has better fermentation quality and higher abundance of Lacticaseibacillus and Levilactobacillus than ensiled forage from other regions. This work may contribute to guiding for silage production in QTP.