Bacterial resource allocation strategies to reduce CO₂ emission and enhance carbon conversion by exogenous additives...

Composting converts organic solid waste into humus to enhance land quality, yet excessive carbon loss in conventional composting limits compost quality. This study explored the mechanisms by which exogenous additives enhance organic carbon conversion and humus synthesis, analyzing the distinct roles of shaping bacterial community structure and resource utilize in malonic acid addition group (MA) and biochar addition group (BR). Compared to CK, cumulative CO₂ emission release reduced by 33.1 % and 37.9 % in MA and BR, respectively. SPEC-OCCU showed fewer specialized species in MA (24) and BR (11) compared to CK (30), yet the additive groups demonstrated higher carbon conversion efficiency. This disparity likely stems from the differential effects of the two additives on bacterial communities. Biochar promoted dominant bacterial growth by optimizing the micro-environment and reducing inter-specific interaction, while malonic acid weakened the interactions by inhibiting specific bacterial metabolisms, thereby increasing resource use efficiency. Co-occurrence networks and humus synthesis associated ASVs showed that additives increased the phyla of keystones and key species, thereby reshaping the bacterial community towards more efficient humus synthesis. Mantel test and Procrustes analysis further suggested that rare taxa play a crucial role in humus synthesis. These findings provide insights into the differential contributions of abundant and rare taxa in composting with additives and offer new perspectives on bacterial community interactions.