Stabilization mechanisms and contributions of mineral-associated microbial necromass to soil organic carbon in coastal wetlands

This study investigates the contributions of microbial necromass carbon (MNC) and mineral-associated organic carbon (MAOC) to soil organic carbon (SOC) pools in coastal wetlands and explores the mechanisms underlying their stabilization. Using amino sugar biomarkers and chemical extractions across three coastal wetland soil profiles (0–100 cm), we found that MAOC contributed an average of 74.9% of SOC, suggesting the importance of mineral protection in long-term carbon storage. Although MNC represented only 20.9% of the MAOC pool, on average 70.9% of total MNC was associated with minerals, indicating a coupled interaction between the “microbial carbon pump” and the “mineral carbon pump”. The findings further reveal distinct mineral stabilization pathways for fungal and bacterial necromass. Clay and amorphous aluminum oxides were found to enhance the stabilization of both MAOC and fungal necromass, while exchangeable calcium supported the protection of bacterial necromass. In contrast, iron oxides played a comparatively minor role. Cross-ecosystem comparisons pointed to a potential saturation threshold for MAOC accumulation, although no such saturation was observed for mineral associated MNC in this study. These findings highlight the ecosystem-specific nature of mineral-organic matter interactions and provide new insights into the role of MNC in the long-term SOC stabilization in coastal wetlands.