Impacts of wetland degradation on soil microbial networks and functions in northern China

• Degradation of wetland alters soil properties and microbial diversity. • The complexity of microbial networks declines as wetlands degrade. • Carbon metabolism is a key microbial function during wetland degradation. • Soil NH 4 + and pH drive changes in microbial communities and functions. • Scrub swamps have the highest nitrogen nutrient availability and microbial diversity. Wetlands are widely distributed across various regions of the Northern Hemisphere and play a critical role in the Earth’s carbon sink. Currently, anthropogenic activities have greatly affected the natural environment of wetlands, subsequently altering the trajectory of ecosystem transition. However, how wetland degradation alters the stability and functioning of soil microbial networks—a critical regulator of carbon and nitrogen cycling—remains to be further investigated. A comprehensive study conducted in the Sanjiang Plain, China, examined microbial and functional changes across four wetland types along a degradation gradient: jungle swamp, scrub swamp, wet meadow, and marshy meadow. Analysis revealed three key findings: First, soil properties and microbial communities varied significantly across degradation stages, with scrub swamps exhibiting the highest nitrogen availability and microbial diversity, supported by elevated nifH gene abundance and nitrogen fixation potential. Second, degradation destabilized microbial networks, as evidenced by a progressive reduction in microbial connectivity from jungle swamps to marshy meadows. Third, carbon metabolism emerged as the most critical microbial function during degradation, with soil NH 4 + and pH identified as primary environmental drivers of microbial community structure and function. These findings provide critical insights into the ecological consequences of wetland degradation and offer a scientific foundation for the development of targeted conservation strategies in these vulnerable ecosystems.