Abstract: Coastal wetlands are blue carbon ecosystems with critical importance for global carbon cycling and climate change mitigation. Although vegetation types could regulate soil environments and thereby influence soil orga-nic carbon (SOC) accumulation and stability, the spatial distribution of microbial necromass carbon (MNC) and its relative contribution to SOC under different vegetation types remain poorly understood. We collected soil samples from three depths (0-10, 10-20, and 20-30 cm) from four dominant vegetation types in the Minjiang River estuarine wetland (Phragmites australis, Cyperus malaccensis, Spartina alterniflora, and Kandelia candel), aiming to analyze the vertical distribution of SOC and MNC and elucidate the regulatory mechanisms. Results showed that in the surface layer (0-10 cm), P. australis and C. malaccensis exhibited higher SOC, MNC, bacterial necromass carbon (BNC), and fungal necromass carbon (FNC) contents than K. candel and S. alterniflora soils. Notably, MNC contents in P. australis and C. malaccensis soils reached 4591.54 and 4832.96 mg·kg^-1 respectively, substantially exceeding those in S. alterniflora and K. candel soils. In the 10-20 cm layer, vegetation type did not affect SOC, MNC, and FNC, although BNC in P. australis significantly exceeded that in S. alterniflora. In the 20-30 cm layer, vegetation type did not affect SOC, MNC, BNC, and FNC. Both SOC and MNC contents decreased with increasing depth, while the FNC/BNC ratio increased. Across all vegetation types, the contribution of FNC to SOC (>15%) was significantly higher than that of BNC (<6%). Soil total nitrogen (TN) and pH emerged as the dominant environmental factors regulating MNC content, with MNC being positively correlated with TN and negatively correlated with pH. In summary, different vegetation types regulated the vertical distribution of SOC and MNC by altering soil TN and pH. Among them, P. australis and C. malaccensis wetlands exhibited substantially higher SOC accumulation and MNC content in surface soils, underscoring their importance in enhancing blue carbon sequestration in the Minjiang River estuarine wetland.

Key words: coastal wetland, plant invasion, soil organic carbon, microbial necromass carbon