Coupled Effects of Water Depth, Vegetation, and Soil Properties on Soil Organic Carbon Components in the Huixian Wetland of the Li River Basin

Wetland ecosystems are essential to the global carbon cycle, and they contribute significantly to carbon storage and regulation. While existing studies have explored the individual effects of the water depth, vegetation, and soil properties on the soil organic carbon (SOC) components, a comprehensive study of the interactions between these factors is still lacking, particularly regarding their collective impact on the composition of the SOC in wetland soils. This paper focused on the Huixian Wetland in the Li River Basin. The variations in the SOC and its fractions, namely dissolved organic carbon, microbial biomass carbon, light fraction organic carbon, and mineral-associated organic carbon, under different water depths and vegetation conditions were examined. Additionally, the effects of the water depth, vegetation, and soil properties (pH and bulk density, total phosphorus (TP), total nitrogen (TN), ammonium nitrogen (NH4-N), and nitrate nitrogen (NO3-N)) on the changes in the SOC and its components were quantified. Specific water depth–vegetation combinations favor SOC accumulation, with Cladium chinense at a water depth of 20 cm and Phragmites communis at 40 cm exhibiting a higher biomass and higher SOC content. The SOC components were significantly and positively correlated with plant biomass, TP, TN, and NH4-N. The coupling of water depth, vegetation, and soil properties had a significant effect on the SOC components, with the coupling of water depth, vegetation, and soil properties contributing 74.4% of the variation in the SOC fractions. Among them, water depth, plant biomass, and soil properties explained 7.8%, 7.3%, and 6.4% of the changes, respectively, and their interactions explained 25.6% of the changes. The coupling of the three significantly influenced the changes in the SOC components. Optimal water level management and the strategic planting of wetland vegetation can enhance the carbon storage capacity and increase the SOC content. This research offers valuable insights for effectively managing wetland carbon sinks and soil carbon reserves.