Organic carbon mineralization and its temperature response of soil organic matter fractions in the Yellow River estuary wetland

The temperature response of carbon dynamics varies with soil organic matter (SOM) fractions, which is of great significance for a better understanding of carbon–climate feedback. However, it is currently unclear how the mineralization-temperature response of SOM fractions occurs and what the main factors are in estuary wetlands. For this purpose, we collected three typical wetland soils in the Yellow River Estuary: freshwater wetland soil (FW), saltmarsh wetland soil (SW), and paddy field soil (PF); obtained two SOM fractions, particulate organic matter (POM) and mineral-associated organic matter (MAOM); investigated carbon mineralization (C_min) and temperature sensitivity (Q₁₀) of two fractions; and determined the effects of soil properties, iron oxides, and substrate quality. Over the 70-d incubation period, both C_min and Q₁₀ differed significantly among the soil types and fractions. The means of C_min and Q₁₀ were 40.1–431.0 μg C·g⁻¹ and 1.04–2.51, respectively, with higher values for FW and PF soils than those for SW soil. Across SOM fractions, POM had higher C_min and Q₁₀ compared to MAOM. Substrate quality (organic carbon in SOM fractions), iron oxides (Fe_o and Fe_d), and soil properties (pH and electrical conductivity (EC)) all exhibited significant effects on carbon mineralization and temperature response. Specifically, pH and EC had negative, and iron oxides positively affected C_min and Q₁₀. However, SOM fraction quality had the opposite effect, with POM having a positive effect on C_min and MAOM having a negative effect on Q₁₀. Among all the factors, the effects of POM on C_min and MAOM on Q₁₀ were dominant. These results suggest that effectively distinguishing the different contributions of SOM fractions is crucial for predicting the carbon–climate feedback in estuary wetlands.