Abstract: The effects of reclamation on soil organic carbon (SOC) in marsh wetlands have been widely investigated, while research on coastal saline marshes is scarce, especially for soil inorganic carbon (SIC). Thus, it is difficult to comprehensively evaluate the impacts of reclamation on soil total carbon (TC). In this study, soil samples from 0-15 and 15-30 cm layers of Qilihai saline marsh wetland and the corresponding long-term reclaimed farmland (about 60 years) in Tianjin were collected and subsequently separated into four aggregate-size classes using wet sieving: >2, 0.25-2, 0.053-0.25 and <0.053 mm. After long-term reclamation, mass proportions of macroaggregates (>2 mm) decreased significantly (-48.1% and -58.1%) while microaggregates(0.053-0.25 mm) increased significantly (+166.1% and +70.0%) in the surface and subsurface soils, respectively. SOC contents decreased by 31.2%-56.8% in all aggregate sizes. The content of SIC in small macroaggregates (0.25-2 mm) and mineral fractions (<0.053 mm) increased significantly (+85.4% and +75.4%) in the surface soil. SIC contents increased significantly by 182.3%-448.2% in all aggregate sizes in the subsurface soil (15-30 cm). The TC content of large macroaggregates (>2 mm) and small macroaggregates (0.25-2 mm) reduced significantly in the surface soil (-12.9% and -21.9%), but TC contents of microaggregates (0.053-0.25 mm) and mineral particle fractions (<0.053 mm) in the surface soil and soil aggregates in the subsurface soil did not change. SIC contents demonstrated a significant compensation for the reduction of SOC contents following reclamation, which slows down or restrains TC loss in coastal salinized marsh wetlands. Therefore, the reclamation induced dynamics of SIC and its impact on total C should be paid more attention in future, especially in coastal saline areas.

Key words: natural spruce-fir forest, dominant tree species, competition.