The responses of soil bacterial and archaeal communities to coastal embankments in three typical salt marshes of Eastern China

Aims
Although the influences of coastal embankments on soil physicochemical properties and carbon (C) and nitrogen (N) cycling have been widely reported, the mechanisms of their effects on soil microbial ecologies remain poorly understood. Thus, the aim of this study was to investigate the variations in the diversity and composition of soil bacterial and archaeal communities between natural and embanked saltmarshes, as well as the determinants that drive these variations.

Methods
16S rRNA gene sequence analysis was performed to assess the impacts of coastal embankments on the bacterial and archaeal communities of native Suaeda salsa, Phragmites australis, and invasive Spartina alterniflora saltmarshes on the east coast of China.

Results
Embankments were found to significantly decrease the microbial diversity of S. alterniflora salt marsh, while increased the OTU richness of P. australis salt marsh. Embankments modified the compositions of soil bacterial and archaeal communities in both S. alterniflora and P. australis salt marshes. However, variations in the microbial diversity, richness, and community compositions between the native and embanked S. salsa salt marshes were insignificant.

Conclusions
These results were possibly because the embankment significantly altered soil nutrient substrate levels (e.g., soil organic C and N) by variations in plant residues and soil physiochemical properties in S. alterniflora and P. australis saltmarshes, whereas the embankment had no observable changes in the soil nutrient substrate and plant residue in S. salsa saltmarsh. This study also elucidated the effects of coastal embankments on biogeochemical cycles, and highlighted their potential hazards to ecosystems.