Insight into the effect of nitrogen-rich substrates on the community structure and the co-occurrence network of thermophiles during lignocellulose-based composting

Thermophilic microorganisms play vital roles in the composting process. To elucidate how raw materials affect thermophilic microbial community composition and their interactions, the succession of thermophilic bacterial and fungal communities were monitored in reed straw co-composting with four common nitrogen-rich substrates. The results of high-throughput sequencing showed that raw materials and composting process significantly changed bacterial and fungal community composition. Firmicutes and Actinobacteria drove the assembly of bacterial communities, while Ascomycetes drove the assembly of fungal communities. Network analysis indicated that during the composting process, the addition of nitrogen-rich sources abundant in easily degradable substances promoted the complexity of thermophilic microbial network. Moreover, microorganisms mainly exhibited synergistic effects, and inter-kingdom competition was more intense than intra-kingdom competition. Notably, rare species play essential roles in maintaining the network construction. Our findings provided novel insights into thermophilic microbial community assembly and their co-occurrence networks during the composting process.