Cow dung accelerates the synthesis of humus by regulating the microbial community and function during composting

Composting is a microbial-driven process transforms organic waste into stable products such as humus. The addition of nitrogen-rich amendments like cow dung can accelerate lignocellulose degradation. However, the microbial mechanisms underlying humus formation remain unclear. In this study, we compared humus accumulation, microbial community and functional in rice husk composting systems with and without cow dung. Cow dung markedly accelerated humus formation, with maximum humic carbon reaching 1.805 g/kg at day 8, compared to 1.418 g/kg at day 40 in the control. High-throughput 16S rRNA sequencing and metagenomic analyses revealed that cow dung reshaped microbial community structure and network complexity, enhancing diversity and functional specificity. Notably, CAZyme gene abundance was significantly higher in the cow dung group during the early stage (days 1–8) and declined as labile substrates were depleted, reflecting temporal functional changes in the microbial community. Thermopolyspora was selectively enriched, serving as a key humus-forming taxon. Thermopolyspora harbors abundant genes involved in the metabolism of aromatic compounds, fatty acids, aromatic amino acids, and aldehyde oxidation. These pathways generate intermediates such as aldehydes, ketones, and carboxylic acids, which serve as precursors for humus synthesis. Overall, cow dung increased the abundance of microbial CAZyme genes, enriched functional microbial abundance, and promoted crude fiber degradation and humus formation. This study deepens our understanding of the microbial-driven humification process and provides a theoretical foundation for the development of targeted strategies to enhance the efficiency and quality of agricultural waste composting, ultimately supporting soil fertility, carbon sequestration, and sustainable agricultural practices. • Cow dung accelerated humus formation and crude fiber degradation. • Cow dung shifted microbial community structure. • Cow dung increases the abundance of CAZyme genes and Thermopolyspora. • Thermopolyspora was contributed to humus formation.