Fungal Necromass Carbon Dominates Global Soil Organic Carbon Storage

Soil organic carbon (C) is derived primarily from plant and microbial necromass; however, the global distribution and contribution of different necromass inputs to soil C storage remain unclear. We conducted a global meta-analysis encompassing 2410 observations from 249 microbial necromass studies and 786 observations from 72 plant residue studies. The results showed that the content of microbial-derived C (10.63 ± 0.39 g C kg^-1 soil) exceeded that of plant-derived C (lignin phenol carbon (LPC), 5.63 ± 0.45 g C kg^-1 soil), across the 0-100 cm soil profile, with fungal necromass carbon (FNC; 7.24 ± 0.21 g C kg^-1) contributing the most to soil C-a pattern consistently observed across all depths. In addition, in the topsoil (0-20 cm), forests (9.39 ± 1.22 g C kg^-1) and grasslands (9.73 ± 1.74 g C kg^-1) showed significantly higher LPC contents than croplands and wetlands; therefore, cropland expansion significantly reduces microbial- and plant-derived carbon stocks in topsoil. Global FNC, BNC, and LPC stocks were estimated to be 211 Pg (95% CI: 156-270 Pg), 71 Pg (95% CI: 59-88 Pg) and 168 Pg (95% CI: 151-186 Pg) in topsoil, respectively. Lower soil pH and mean annual temperature were associated with higher FNC, BNC, and LPC contents, particularly in high-latitude regions like North America. These results demonstrate that microbial necromass, rather than plant residues, dominates soil C storage globally. These findings highlight the need for management strategies that address both land-use change and rising temperatures to protect microbial and plant C pools.