Soil fungal distribution and environmental drivers in reclaimed salt marshes of the Yangtze River estuary

Coastal salt marshes are important blue carbon (C) reservoirs, and reclamation has a profound impact on their microbial communities. However, little is known about the successional patterns and driving mechanisms of soil fungal communities, which are crucial to soil organic matter turnover during long burial duration after reclamation. Salt marsh soils of reclamation areas with different construction times on Chongming Island in the Yangtze River Estuary, China, were investigated in this study. Using high-throughput sequencing, we systematically characterized the distribution patterns of fungal communities and their environmental constraints. The results showed that with increasing burial duration and depth, soil total organic carbon (TOC) content and total nitrogen (TN) content declined significantly, accompanied by reduced fungal diversity and pronounced shifts in community structure. Ascomycota was the absolute dominant group, with relative abundance increasing with depth, indicating strong adaptation to oligotrophic environments. Community succession revealed a clear ecological strategy shift, as taxa favoring fresh organic matter (e.g., Unclassified_c__Sordariomycetes) were replaced by stress-tolerant fungi adapted to salinity (e.g., Meyerozyma ) and nutrient depletion (e.g., Cutaneotrichosporon ). This shift in fungal strategies may influence the stability of buried C by modifying fungal-mediated C turnover. Redundancy analysis confirmed that burial duration was the most important driver of fungal community succession (r² = 0.313, p = 0.001), while soil TOC, clay content, TN, and pH were key physicochemical factors. This study elucidates the long-term successional trajectory of fungal communities in salt marsh soils driven by reclamation and highlights nutrient depletion-induced environmental filtering as the core mechanism. These findings provide a critical microbial perspective for understanding the long-term evolution of coastal ecosystems.