Abstract: Microbial necromass carbon (MNC) constitutes a significant component of soil organic carbon (SOC) and plays a crucial role in soil carbon sequestration. However, the accumulative contribution and impact mechanism of MNC to organic carbon fractions across different wetlands remain unclear. In this study, we analyzed the accumulative contribution and impact mechanism of microbial necromass carbon to particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) in the 0-40 cm soil layer of these three wetland types in the Xiaoxing’an Mountains, including typical natural forested swamps, shrub swamps, and marshes. The results showed that: 1) Soil organic carbon fractions (MAOC and POC) decreased with soil depth across the three wetland types. Shrub swamp soil exhibited the highest MAOC contents (109.96 g·kg^-1), while marsh soil had the highest POC contents (22.74 g·kg^-1). 2) In forested swamps and shrub swamps, the proportion of MNC in MAOC in the 0-20 cm soil layer (42.9% and 23.1%) was higher than that in POC (25.6% and 14.1%). Similarly, in the 20-40 cm layer, the values (41.1% and 9.6%) were also higher than those in POC (12.4% and 6.6%). In marshes, the proportion of MNC in MAOC (31.0%) was higher than that in POC (13.2%) in the 0-20 cm soil layer, whereas the proportion of MNC in MAOC (8.2%) was lower than that in MAOC (24.8%) in the 20-40 cm soil layer. 3) In forested swamps and shrub swamps, pH and SOC were key factors regulating the partitioning of MNC contributions to orga-nic carbon fractions, whereas SOC dominated MNC allocation in marshes. By revealing the distribution patterns and influencing factors of MNC in organic carbon fractions across different wetlands in the Xiaoxing’an Mountains, our results enrich understanding on the microbial carbon pump theory in wetland soils.

Key words: swamp/marsh, soil organic carbon, microbial necromass carbon, particulate organic carbon, mineral-associated organic carbon