Divergent responses of soil organic and inorganic carbon driven by land use during coastal reclamation.

Coastal reclamation fundamentally transforms natural tidal flat ecosystems into managed terrestrial landscapes, initiating profound shifts in soil physicochemical properties and carbon dynamics; understanding how reclamation history and land use jointly regulate soil carbon fraction dynamics is essential for evaluating carbon sequestration potential in rapidly expanding reclaimed coastlines. Here, we show that reclamation induces progressive desalination, surface dealkalization, nutrient enrichment, and texture refinement; soil organic carbon increases markedly across reclamation stages, exhibiting strong surface accumulation under woodland and cropland, with mineral-associated organic carbon as the dominant fraction and organic carbon increasingly stable; soil inorganic carbon remains stable during early reclamation but declines markedly in surface layers of long-term reclaimed terrestrial soils while remaining high in aquaculture systems; and organic carbon fractions are primarily associated with nutrient availability and clay content whereas inorganic carbon dynamics are closely linked to soil pH and salinity.