Synergistic effects of biochar and cellulase on carbon emission reduction and humification during co-composting of cattle manure and sugarcane bagasse

Introduction The emission of carbon dioxide (CO₂) and methane (CH₄) during composting not only contributes to the greenhouse effect but also leads to carbon loss, thereby reducing humus production and compromising the quality of the final compost product. This study investigated the efficacy and underlying mechanisms of biochar and cellulase addition, individually and in combination, in mitigating emissions and enhancing compost quality within a cattle manure-sugarcane bagasse co-composting system. Methods By monitoring key composting parameters and combining with high-throughput sequencing analysis of bacterial and fungal communities, the changes of microbial structure and function were evaluated, focusing on organic carbon transformation, humification pathway and greenhouse gas mitigation mechanism. Results and discussion The results demonstrated that compared with the control, the combined application of biochar and cellulase (particularly the treatment with 5% biochar, denoted as MC5) significantly reduced the cumulative emissions of CO 2 and CH 4 by 18.6 and 31.2%, respectively. In addition, the combined treatment promoted the synthesis of humic substances, markedly increased humic acid content by 41.0% (from 28.56 to 40.27 mg/g) and the humification index (HI) by 75.6% (from 2.35 to 4.13). Microbial community analysis revealed that the combined amendment shaped the microbial succession by enriching lignocellulose-degrading fungi (such as Mycothermus ) and humification-promoting bacteria (e.g., Chryseolinea ), while suppressing taxa associated with greenhouse gas emissions (e.g., Clostridium ), thereby directing a greater carbon flux toward humification pathways. This study confirms that the synergy between biochar and cellulase effectively mitigates greenhouse gas emissions and improves the quality of compost, providing a theoretical basis for developing low-carbon, high-value composting technologies.