Unlocking the potential of microbial necromass for enhancing soil carbon sequestration: A global perspective on cropland management using meta-analysis.

The formation and sequestration of soil organic carbon (SOC) in croplands are significantly regulated by microbial necromass, a process strongly influenced by agricultural management. However, how management affects microbial necromass carbon (MNC) and its contributions to SOC stocks from an agroecological perspective remains insufficiently understood. To address this issue, we collected 834 paired aggregated experimental data from 77 studies worldwide, incorporated the influence of climate factors and soil physical and chemical properties, and constructed a necromass carbon database to reveal the impact of cropland management practices on microbial necromass and SOC. Our finding shows that management practices mainly regulate microbial community composition and its metabolic efficiency by altering soil nutrient availability and physical and chemical conditions, promoting the formation and stock growth of MNC, with a contribution rate of 9.1 %-42.2 % to SOC. The highest MNC and SOC increments were observed with the combined application of mineral fertilizers and manure, reaching 0.55 Mg C ha^-1 and 1.39 Mg C ha^-1 respectively. This synergy is likely because mineral fertilizers provide readily available nitrogen that promotes microbial utilization of the organic matter supplied by manure. The total MNC and SOC stocks of this practice were 3.78 Mg C ha^-1 and 4.91 Mg C ha^-1. The proportion of microbial-necromass-derived C in newly-formed SOC increased with the management duration with mineral fertilizers, manure and their combination, indicating that sustained nutrient inputs foster a microbial community efficient in processing organic inputs into stable necromass. Furthermore, long-term mineral fertilization and manure application significantly increased the contribution of microbial necromass to newly sequestered SOC (reaching 46.9 % and 54.5 %, respectively), underscoring the critical role of sustained management. This study emphasizes the critical role of MNC in driving the SOC sequestration of croplands, and advances our understanding of how different management strategies modulate the microbial-driven carbon pathway to promote the dynamic changes of MNC and SOC, highlighting that optimizing microbial community functions through integrated practices is key to enhancing soil carbon sequestration.