Inoculating functional bacteria improved the humification process by regulating microbial networks and key genera in straw composting by adding different nitrogen sources

[Display omitted] •Inoculation increased the degradation of lignocellulosic components by 26.9%–81.6%.•Inoculation increased humus by 15.7%–23.0% in different nitrogen sources composting.•Inoculation strengthened phenolic-protein and Maillard pathways for humification.•Inoculation combined with pig manure had higher network modularity and interactions.•Nitrogen sources led to different key genera related to humification in composting. The aim of this study was to compare the effect of functional inoculant and different nitrogen sources on the relationship among lignocellulose, precursors, and humus as well as their interactions with bacterial genera in straw composting. Results showed that inoculation improved the heating process and retained more nitrate compared to control. Inoculation increased the degradation of lignocellulosic components by 26.9%-81.6% and the formation of humus by 15.7%–23.0%. Bioinformatics analysis showed that inoculation enriched key genera Chryseolinea in complex nitrogen source (pig manure) compost and Pusillimas, Luteimonas, and Flavobacteria in single nitrogen source (urea) compost, which were related to humus formation. Network analysis found that inoculation and urea addition improved the microbial synergistic effect and inoculation combined with pig manure had more complex modularity and interactions. Combining the functional bacterial inoculant with urea helped to enhance the degradation of lignocellulose and humification process during straw composting especially with single nitrogen source.