Soil Organic Carbon Mineralization in Liaohe Wetland: Water-Nitrogen Responses

The tested soils were collected in 2025 from the Qixing Wetland of the Liaohe River Basin, Liaoning Province (122.8°E, 42°N), which is characterized by a temperate semi-humid continental monsoon climate with significantly heterogeneous soil hydrological backgrounds across the region. Based on the inundation status of the original soil-forming processes, the four collected soils were classified into two groups: the non-flooded soil group (Q1), comprising meadow soil (CD) collected from the naturally drought-prone meadow zone at the wetland margin and maize soil (YM) collected from the dryland maize fields adjacent to the wetland; and the flooded soil group (Q2), comprising marsh soil (ZZ) collected from the perennially flooded core zone of the wetland and paddy soil (SD) collected from the surrounding areas under long-term single-season rice cultivation. Surface soils (0–20 cm) of the four tested soil types were collected using a multi-point composite sampling method, sieved through a 2 mm mesh, and divided equally into two portions: one portion was air-dried for the mineralization incubation experiment, and the other was stored at 4°C for subsequent determination of labile carbon and nitrogen fractions and enzyme activities.