Coastal wetlands contain very large carbon stocks – termed as blue carbon – and their management has emerged as a promising nature-based solution for climate adaptation and mitigation. However, the interactions among sources, pools and molecular compositions of soil organic carbon (SOC) in blue carbon ecosystems (BCEs) remain unclear. Here, we study these interactions along a 18,000 km long coastal line of saltmarshes, mangroves, and seagrasses in China. Mineral-associated organic carbon (MAOC) is enriched in allochthonous-dominated BCEs with abundant active minerals, leading to an increased proportion of persistent molecules. More specifically, soils with high allochthonous inputs (> 50%) are characterized by a high presence of MAOC (> 70%) to total SOC and exhibit a notable preservation of lipids (36%) across saltmarshes, mangroves, and seagrasses. The burial of allochthonous particles, derived from external sources such as rivers or tidal influxes facilitates the formation of MAOC, that is stabilized through binding to mineral surfaces or occlusion within microaggregates. Proportions of particulate organic carbon (POC) and MAOC are two important predicators for molecular compositions of SOC. Lipid proportions decrease with increase of POC and autochthonous OC proportions. These findings provide fresh insights into the coupled control over SOC sequestration in BCEs by allochthonous inputs, pools, and persistent organic components.
 

Soil organic carbon; Wetland ecosystems; SOC Sources; SOM composition; Climate Change