Carbon and nitrogen transformation mechanism and functional microorganisms of sheep manure composting on the Qinghai-Tibet Plateau under different moisture content

In this study, metagenomics technology was used to explore the microbial mechanism and functional microorganisms of carbon and nitrogen transformation during sheep manure composting under 45% (S45) and 60% moisture content (S60) on the Qinghai-Tibet Plateau (QTP). Results showed that the organic carbon oxidation was the main step of carbon transformation during composting, and Corynebacterium, Nocardiopsis, Brachybacterium, Brevibacterium, Luteimonas, Pseudoxanthomonas, and Thermobifida were the main participants in this step. The encoding gene abundance of functional enzymes such as cellulase, glucosidase, and chitinase involved in organic carbon oxidation of S45 was higher than that of S60, which resulted in S45 having a higher lignocellulosic degradation rate. In nitrogen transformation, nitrate reduction was the most important nitrogen transformation step in the early stage. As composting proceeded, nitric oxide reduction, nitrite reduction, and nitrite ammonification gradually enhanced. The abundance of functional genes involved in nitrite reduction and nitric oxide reduction in S45 was lower than that in S60, which would result in lower nitrogen loss and higher alkali-hydrolyzed nitrogen content in S45. Nocardiopsis, Corynebacterium, Pseudomonas, Pseudorhizobium, Planifilum, Sphingobacterium, and Luteimonas were the main participants in denitrification. Cellulomonas, Nocardiopsis, Altererythrobacter, Cellulosimicrobium, Devosia, and Streptomyces were the main participants in nitrite ammonification.