Microbial mechanisms of biochar addition on carbon and nitrogen synergistic retention during distilled grain waste composting: Insights from metagenomic analysis.

To elucidate the mechanism of biochar addition on carbon and nitrogen retention during distilled grain (DGW) composting, this study investigated the losses of carbon and nitrogen and functional genes related to carbon and nitrogen metabolisms between biochar-treated and control composts. The addition of biochar significantly increased carbon and nitrogen retention by 13.5% and 33.8%, respectively. The difference in core carbon metabolism genes indicated that biochar addition inhibited CO release and promoted carbon fixation during the later composting phase, leading to improved carbon retention. Nitrogen metabolism analysis indicated that biochar addition suppressed early-phase ammoniation and late-phase denitrification and promoted nitrification and ammonia assimilation during the later stages of composting, thereby preserving nitrogen. During the later composting phase, biochar addition enhanced carbon-nitrogen coupling metabolism activity, leading to the synchronous retention of carbon and nitrogen. These findings elucidate the mechanism of biochar addition on carbon and nitrogen retention during DGW composting.