The role of blue carbon stocks becomes more labile with mangrove development

Soil labile organic carbon (LOC) is a crucial component in carbon cycling in coastal wetlands and serves as an important indicator of SOC. Despite this, little is known about the stabilization of SOC and its LOC during mangrove development. The objective of our study was to quantify SOC and LOC in the soil at depths ranging from 0 to 100 cm across four sites, including a mudflat and three mangrove sites of varying ages (15-, 45-, and 80-yr old) were selected in Yingluo Bay, China. The concentration of SOC, POC (particulate organic carbon), DOC (dissolved organic carbon), MBC (microbial biomass carbon), and KMnO4-C (potassium permanganate-oxidizable carbon) were measured. The CMI (soil carbon management index) was also calculated to precisely and directly reflect the dynamic changes of soil carbon pools. Mangrove natural expansion showed a significant positive effect on both SOC and LOC. The concentration of KMnO4-C in the top 50 cm of soil layer showed a significant increase in three different mangrove forest sites. The POC, DOC and MBC were also significantly increased in response to mangrove development. The 80-yr old mangrove site had the highest SOC concentrations, LOC concentrations, soil carbon lability Index (LI) and CMI among all sites. These findings suggested that the development of mangroves increases soil organic carbon fractions through vegetation production and enhances long-term carbon sequestration rates by expanding soil labile carbon pools. As a management option, promoting the natural expansion of mangroves can maximize the sequestration potential of soil organic carbon.