Contrasting effects of iron minerals on soil organic carbon stability in mangrove wetlands with different salinities

Abstract Background Iron (Fe) oxides are vital for the stability of soil organic carbon (SOC) in wetlands, yet their impact on SOC stability in mangrove wetlands with varying salinity levels remains unclear. In this study, the effects of hematite treatment on soil Fe oxides, biological properties and SOC stability were investigated by adding 0%, 10%, 20% and 50% hematite to low- and high-salinity mangrove soils on the basis of initial total soil Fe content (50 mg g −1 ). Results The results showed that hematite treatments regulated SOC stability mainly by altering Fe-bound organic carbon (OC-Fe), rather than directly affecting SOC content. In high-salinity soils, the hematite treatment increased OC-Fe from 40.64 to 70.07% by promoting the formation of low-crystalline and short-range ordered Fe oxides, dissolved organic carbon preservation, and microbial biomass reduction. In contrast, the hematite treatment reduced the OC-Fe content by 16.06–35.58% by promoting microbial utilization of natural OC-Fe complexes in low-salinity soils. In addition, only the 20% hematite addition treatment increased carbon emissions from low-salinity soils by 22.96%, while all other treatments reduced soil carbon emissions by 4.77–24.48%. Conclusions This study highlights the effects of Fe minerals on SOC stability in mangrove wetlands under different salinities, and provides new insights into the study of carbon storage in different types of mangrove wetlands.