Reduction in soil salinity enhances soil organic carbon stock in the Yellow River Delta

Soil organic carbon (SOC) is essential for terrestrial ecosystems, soil health, and sustainable agricultural development. However, soil salinization impedes SOC sequestration and adversely affects crop productivity. A comprehensive understanding of how soil salinization drives SOC dynamics remains lacking, especially in the Yellow River Delta (YRD). This study investigated the spatiotemporal dynamics of soil salinity (SS) and SOC stock (SOCs) in the YRD during the historical period (2016 to 2022) using multi-source data. To quantify the potential influence of SS changes on SOCs, we simulated different scenarios of SS variation. We then assessed the impact of salinization amelioration on SOCs under future (2030 to 2060) climates. The results indicated that a positive correlation between SOC and SS in non-salinization soil, but a negative correlation in salinized soil. Mitigating SS in salinized soil contributed to increased SOCs, with the most pronounced effects observed in low-salinity soils. From 2016 to 2022, SS decreased while SOCs increased, with the most notable changes occurring in salinized soil, highlighting the effectiveness of salinity reduction in enhancing soil quality. The results further showed that under the anthropogenic amelioration scenarios, SOCs are projected to increase by 2.49 × 106 Mg (SSP245) and 1.68 × 106 Mg (SSP585) by 2060. These gains stand in sharp contrast to the projected losses of 3.36 × 106 Mg and 4.38 × 106 Mg under natural variation scenarios without human intervention. As a result, sustained efforts in soil salinization amelioration are crucial for reducing SS, strengthening SOC sequestration capacity, and realizing the “dual carbon” goals.