Salinity drives shifts in soil microbial community composition and network complexity along vegetation community succession in coastal tidal flats

The changes in soil microbial characteristics following vegetation succession in coastal tidal flats are poorly understood. Understanding the soil microbial change pattern can help us better manage tidal flat ecosystems. With increasing distance from the seaside, succession occurs in bare tidal flat, Spartina alterniflora, Suaeda salsa, Imperata cylindrica, Phragmites communis, and Sesbania cannabina. Soil samples collected at distinct vegetation succession sites were measured in terms of the contents of total soluble salt (TS) and specific ions, pH, soil organic matter and bacterial and arbuscular mycorrhizal fungi (AMF) community composition. The salt ion contents (except for bicarbonate -HCO3-) decreased as vegetation succession occurred. Compared to the bare tidal flat site, the bacterial and AMF diversity and richness increased in vegetation-covered soil. The microbial network of the late succession stages (Imperata cylindrica, Phragmites communis and Sesbania cannabina) indicated a more complicated structure with more nodes and links and higher modularity than that of the early succession stages (bare tidal flat, Spartina alterniflora and Suaeda salsa). Redundancy analysis revealed that TS, Cl-, SO42-, HCO3- and Na+ significantly influenced the bacterial and AMF (including Mg2+) community structure. TS, SO42-, Ca2+ and Mg2+ exhibited a strong negative relationship with the bacterial Shannon diversity (conducted at the operational taxonomic unit level), and the correlation coefficient ranged from-0.93 to-0.97; soil organic matter indicated a significant negative correlation with the AMF diversity, at a correlation coefficient of-0.92. The correlation between the microbial species and salt ions exhibited complexity and ion specificity. It was concluded that salinity is the key factor driving shifts in soil microbial community composition and network complexity during coastal vegetation succession considering ion-specific effects.