Plant life form, biomass allocation, and belowground structure shape depth-dependent soil organic carbon accumulation as blue carbon sources in vegetated tidal flats

Korean tidal flats are gaining attention for their high potential as blue carbon storages, but research on vegetated areas remains limited. To address this gap, this study examined the vertical distribution of soil organic carbon (SOC) in halophyte-vegetated tidal flats on Korea's west coast and investigated how plant life form, biomass allocation, and belowground structure are associated with SOC accumulation and stabilization, using measurements of plant organ biomass and SOC at multiple depths. The results showed clear differences in SOC distribution among vegetation types. SOC in perennial herbaceous plant communities was 1.2 times higher than that in annual herbaceous plant communities. Furthermore, in tidal flats dominated by perennial vegetation, the contribution of belowground halophyte-derived organic carbon to soil organic carbon increased in proportion to belowground biomass organic carbon ( p < 0.001). In vegetated areas, belowground carbon (BGC) showed the strongest association with SOC accumulation among the vegetation-related variables examined, and differences in SOC distribution among plant communities reflected variation in belowground biomass allocation and structure. These findings demonstrate that the vertical distribution and stabilization of SOC in vegetated tidal flats are closely linked to halophyte belowground productivity and highlight the potential for targeted restoration and management of perennial herbaceous vegetation to enhance blue carbon storage, thereby contributing to climate change mitigation and the long-term resilience of coastal ecosystems. • Vegetated tidal flats stored 1.33 times higher SOC than bare tidal flats • Perennial herbaceous plants enhanced deeper and more stable SOC accumulation • Belowground biomass was strongly associated with SOC storage in vegetated flats • SOC in bare tidal flats was mainly controlled by soil physicochemical properties • Temperate tidal flats function as significant blue carbon reservoirs