Response Patterns of Soil Organic Carbon Fractions and Storage to Vegetation Types in the Yellow River Wetland

To promote soil carbon (C) sequestration and alleviate climate change, it is crucial to understand how vegetation types affect soil organic C (SOC) storage and stability in riverine wetlands. This study investigates the characteristics of SOC fractions and storage among different vegetation types and evaluates their soil C sequestration potential. Soil samples were collected and analyzed from four vegetation types (Typha orientalis, Tamarix chinensis, Avena sativa, and Phragmites australis) in wetlands at the junction of the middle and lower reaches of the Yellow River. Soil particulate organic C, dissolved organic C, and microbial biomass C contents of Avena sativa and Phragmites australis communities were higher than those of Tamarix chinensis and Typha orientalis communities (p < 0.001). Typha orientalis communities exhibited the highest SOC stability (4.31 ± 0.38), whereas Tamarix chinensis communities showed the lowest (1.34 ± 0.17) (p < 0.001). Soil organic C storage of Avena sativa (2.81 ± 0.32 kg m−2) and Phragmites australis (2.53 ± 0.06 kg m−2) communities was higher than that of Tamarix chinensis (0.88 ± 0.06 kg m−2) and Typha orientalis (1.35 ± 0.13 kg m−2) communities (p < 0.001). Soil electrical conductivity (EC) was significantly correlated with SOC fractions of Typha orientalis and Phragmites australis communities, while soil water content and particle size composition affected SOC fractions of Avena sativa communities (p < 0.05). Soil particle size composition affected the SOC storage of Typha orientalis, Tamarix chinensis, and Avena sativa communities (p < 0.05). Soil pH, water content, and EC influenced the SOC storage of Typha orientalis, Tamarix chinensis, and Phragmites australis communities (p < 0.05). These results demonstrate that Avena sativa and Phragmites australis communities play a vital role in maintaining C sink potential and ecological function in the Yellow River wetland. Nonetheless, the Typha orientalis community had greater C sequestration in the long term due to its high SOC stability. This research suggests that the effects of vegetation types should be considered when exploring the soil C cycle in riverine wetlands.