Microbial inoculation influences bacterial and autotrophic community assembly in cow dung–cotton straw composting to promote carbon sequestration and humification

Inoculation with microbial agents affects the composition and assembly of microbial communities in compost, subsequently improving the stability and humification of the material carbon pool. However, the effects of carbon sequestration and humus components on microbial community assembly processes during composting are still unclear. To address this, we established control (CK) and inoculation (TG) treatments based on a multifunctional microbial agent. The results showed that inoculation increased the β -glucosidase, acetyl-CoA synthase, polyphenol oxidase, peroxidase, and pmoA enzyme activities in compost. These composting characteristic changes stimulated carbon retention and humification, resulting in final total organic carbon (TOC) and humic-substance (HS) contents enhanced by 11.8% and 14.8%, respectively. Deterministic and stochastic processes dominated the assembly process of bacterial and cbbL -containing autotrophic (CCA) communities, respectively. Inoculation also increased the complexity and stability of microbial networks while strengthening the contribution of abiotic and biotic factors in reshaping the structure of bacterial and CCA communities. The norank_f_A4b , Paracoccus , and Rhodospirillum genera were identified as the key taxa in TG affecting the construction of microbial communities. TOC and HS were the main driving factors for community assembly, wherein they regulated the assembly process of the CCA community by affecting the α -diversity and key taxa. Interestingly, we also found that bacteria may mediate the assembly of CCA communities. The results of this study provide valuable insights for effective carbon-oriented humification practices in composting and for improving the fertility and economic benefits of composting. • Inoculation inhibited CO 2 and CH 4 emissions during cow dung–cotton straw composting. • Inoculation enhanced the TOC and HS contents by 11.8% and 14.8%, respectively. • Microbe–environment interactions improved C humification and network dynamics. • Biotic factors and community assembly played vital roles in carbon directional humification.