Calcium peroxide and composite microbial inoculant synergistically promote compost humification by enhancing lignocellulose degradation and modulating microbial communities

This study examined the effects of a combined calcium peroxide and lignocellulose-composite microbial inoculant on lignocellulose degradation and humification during composting, and investigated potential microbial mechanisms using metagenomics. The results showed that the combined treatment enhanced the abundances of lignocellulose-degrading enzyme genes (e.g., AA1, AA2, GH3, GH10) during the high-temperature phase, promoted lignocellulose degradation, and reduced the abundance of denitrifying bacteria (such as Lutimonas ) in the later stages. This led to increase in nitrogen retention, and enhanced the abundance of core microbial phyla (e.g., Actinomycetota, Ascomycota) in the later stages, thereby optimizing the humification process. Specifically, the lignocellulose degradation rate increased to 45.39%, the nitrate nitrogen content rose to 26.09 mg/kg, and the humic acid (HA) content increased to 74.10 mg/L. Network analysis showed that the combined treatment enhanced the positive correlation between microbial communities and auxiliary enzyme activities (AA) and glycoside hydrolases (GH), thereby improving the energy utilization efficiency of the composting process. Furthermore, we identified GH1, GH44, GH30, and GH113 as key GH families that may play essential roles in HA and humic substance (HS) synthesis. These findings provide new strategies for enhancing the microbial conversion of lignocellulose into humus. • The co-application promoted the degradation of organic matter and lignocellulose while improving the compost product’s quality, with the final compost exhibiting high humification (HA/FA = 2.01), low phytotoxicity (GI = 145.92%), and excellent nitrogen retention capacity (NO 3 - -N = 26.09 mg/kg). • The co-application boosted the abundance of lignocellulose-degrading enzyme genes during the thermophilic phase • The co-application effectively reduced the relative abundance of denitrifying bacteria and promoted the enrichment of core microbial phyla throughout the composting process. • Co-application enhanced interactions between microbial communities and lignocellulose-degrading enzyme genes, thereby improving degradation efficiency.