The nature of soil blue carbon varies across mangrove geomorphic settings

Abstract Mangrove forests store significant amounts of blue carbon, mainly as soil organic matter. Insights into mangrove organic matter are limited, despite its importance for understanding blue carbon accumulation and vulnerability to global change. Here, we quantified soil organic matter preserved through chemical recalcitrance and association with the mineral phase, as key factors influencing blue carbon persistence. We found that the nature of the soil organic matter varied with mangrove geomorphic settings. Delta settings were dominated by presumably the most persistent soil organic matter associated with minerals, while open coast karstic settings contained mostly particulate soil organic matter, likely preserved due to low microbial activity. Across mangrove soil depths, there was little difference in soil organic matter pools. The soil organic matter pool across mangroves’ geomorphic settings exhibited greater variation than that observed across all terrestrial biomes. These findings underscore the need to tailor mangrove conservation and restoration to geomorphic settings.