The distribution of the soil aggregate structure and its associated organic carbon along the elevation gradient remains unclear, but it may be crucial for the stabilization of soil carbon pools in mountainous forests. In this study, we first assessed the changes in aggregate-associated organic carbon and the aggregate structure in the 0–20 cm soil layers of an alpine forest in the Sygera Mountains along an elevation gradient (3000–4200 m). We then conducted an incubation experiment to explore the relationship between aggregates and soil organic carbon mineralization, using the Pearson correlation analysis and RDA. The results indicated that macroaggregates and microaggregates were the predominant forms of aggregates in the Sygera Mountains, contributing significantly to organic carbon (33.57% and 38.29%, respectively). As the elevation increased, the stability of aggregates in mid and high elevations (3600–4200 m) was significantly higher than that in low elevations (3000–3300 m). Aggregate stability and macroaggregate-associated organic carbon were positively correlated with the total soil organic carbon, suggesting that organic carbon is essential for promoting soil aggregation in forest soils. With the rising temperatures, the rate of soil mineralization at different elevation sites significantly increased, and the Q₁₀ values were greater at low elevations than at mid and high elevations. This implied that soil carbon pools at low elevations were more sensitive to climate warming. The significant negative correlation between microaggregate-associated organic carbon and soil mineralization suggested that microaggregates contribute to the stabilization of soil carbon pools. Given that the link between aggregates and soil mineralization strengthened with increasing temperatures, the role of aggregates in the stabilization of forest soil carbon pools should be emphasized under a warming trend.

The interactions between iron oxides and organic carbon within the particulate organic matter (POM) and mineral-associated organic matter (MAOM) fractions in paddy soils remain insufficiently understood, yet they are likely crucial for unlocking the carbon sequestration potential of these systems. In this study, we investigated the distribution of soil iron oxides and organic carbon within POM and MAOM fractions following 10 years of continuous irrigation and organic amendment management. We also examined the relationship between iron oxide transformation and these two SOC (soil organic carbon) fractions. Our results demonstrated that, under both flooded irrigation and controlled irrigation regimes, straw return or manure application effectively enhanced soil carbon sequestration, as evidenced by increases in both POM-C (POM-associated organic carbon) and MAOM-C (MAOM-associated organic carbon) contents. Meanwhile, exogenous carbon inputs promoted the transformation of crystalline iron oxides into short-range ordered iron oxides and iron oxide colloids, thereby enhancing the activation and complexation degree of soil iron oxides and facilitating the formation of Fe-bound organic carbon. Further regression analysis revealed that the activation degree of iron oxides had a stronger influence on POM-C, whereas the complexation degree had a greater effect on MAOM-C. This implies that exogenous carbon inputs are effective in promoting soil carbon sequestration in both flooded and water-saving irrigated rice paddies and that iron oxide transformation plays a key role in mediating this effect.