Intensive input of labile carbon and mineral nitrogen enhancing the sequestration organic carbon across soil aggregates

Soil carbon (C) cycling is strongly influenced by inputs of labile organic carbon (LOC) and mineral nitrogen (N), yet how these inputs interactively affect soil organic carbon (SOC) turnover remains poorly understood. This study investigates how glucose (as a LOC source) and two mineral N forms collectively regulate SOC dynamics at the aggregate scale. All treatments enhanced SOC storage, with glucose (CT), glucose + ammonium (CA) and glucose + nitrate (CN) increased SOC by 9.60 %, 7.38 % and 5.91 %, respectively. Elevated SOC aliphaticity under N amendments suggested enhanced microbial assimilation, particularly via fungal-dominated networks. Furthermore, organic carbon (OC) degradation genes were upregulated in the order: CT > CN > > CA, indicating that combined N and C inputs significantly mitigated SOC biodegradation. The decrease in readily oxidizable C under CA treatment implied greater microbial assimilation, with subsequent transformation into recalcitrant organic fractions. At the aggregate scale, CT predominantly increased SOC in large macro-aggregates, whereas CN and CA promoted greater SOC accumulation in small macro-aggregates and micro-aggregates. CN and CA also increased N-alkyl and methoxyl C in micro-aggregates, confirming enhanced N assimilation within these aggregates. In contrast to bacterial dominance, fungal contributions to SOC dynamics became progressively more important with decreasing aggregate size. Overall, glucose was protected in larger aggregates during macro-aggregates formation, while microbial assimilation promoted SOC sequestration in smaller aggregates. These findings advance our understanding of SOC transformation under C and N interactions, providing novel insights for optimizing SOC sequestration via strategic organic/inorganic input management.