From paddy fields to natural wetlands: Soil quality across successional stages

Natural succession following farmland abandonment promotes ecological restoration of wetland soils, yet systematic studies on soil property and quality trends in wetlands over time are scarce. This study evaluated the dynamic changes in soil physicochemical properties and quality across wetlands with varying abandonment durations to elucidate drivers of soil quality restoration. Five sites were selected in the downstream Tumen River, China: paddy fields (PF); restored wetlands abandoned for 5 (Ab5), 15 (Ab15), and 30 years (Ab30); and natural wetlands (NW). Principal Component Analysis was employed to evaluate the relationship between abandonment duration and soil property changes, while Minimum Data Set was used to assess soil quality, with total nitrogen, available nitrogen, total phosphorus, and available phosphorus as core indicators. The results revealed significant differences in soil properties between the upper and lower soil layers, with the most pronounced differences observed in Ab5 compared to other restored wetlands. Total nitrogen had the greatest influence on the soil quality index at both soil depths. The upper soil layer gradually recovered with succession, although agricultural activities still contributed to nutrient loss, while lower layer recovery lagged behind. Ab30 exhibited the highest soil quality index, followed by Ab15, Ab5, NW, and PF, confirming the positive effect of succession on soil quality. These findings highlight critical soil indicators, offering insights for the restoration and sustainable management of degraded wetlands. These findings can be integrated into adaptive management strategies to enhance ecological resilience and promote sustainable land use.