Microbial Necromass Dynamics and Its Contribution to Soil Carbon Storage

Soil organic carbon (SOC) is a critical regulator of soil health and global climate. Although SOC was traditionally considered to originate predominantly from plant derived inputs, recent evidences indicate a conceptual shift toward microbial necromass as a stable contributor to SOC. Microbial necromass (MN) consists of residues of microorganisms after death, like cell wall components and other biomolecules, which exhibit a strong affinity for mineral surfaces and are physically protected within soil aggregates, enabling long-term stabilization. The primary stabilization mechanisms include mineral association and protection within aggregates. Mineral-associated organic matter (MAOM) is the most persistent pool of SOC. Although biomarkers such as amino sugars are widely used to quantify microbial necromass, they are sensitive to environmental variability. Emerging techniques like NanoSIMS and isotopic tracing methods assist in overcoming existing spatial and temporal limitations. Besides, MN accounts for more than half of the total soil organic carbon and facilitates long-term carbon sequestration. MN is highly susceptible to environmental variability and also depends on microbial growth and carbon use efficiency. In this review, we summarize the mechanisms behind the necromass formation, stabilization, the factors controlling and identify major research needs for quantification and understanding the nature of MN in various climatic conditions.