The impacts of saltwater intrusion and sea level rise on plant and microbial communities of coastal wetlands

Coastal freshwater forested wetlands provide important ecosystem services, yet are threatened by saltwater intrusion and sea level rise (SWISLR). In these systems, SWISLR is leading to increased marine salt exposure, soil alkalinization, and inundation. Remote sensing has revealed that nearly 10% of forested wetlands in the North American coastal plain have transitioned to shrubland or marsh since 1996. Despite the scale and importance of these community shifts, how the multivariate effects of SWISLR impact plant and microbial community turnover and diversity remains unresolved. In this study, we investigate the drivers of plant and microbial community turnover, diversity, and forest loss. We established three transects representing space-for-time gradients of saltwater exposure in the Albemarle-Pamlico Peninsula of North Carolina, USA. Along each transect, we surveyed plant community composition and collected soil cores for sequencing fungal (ITS2) and bacterial (16S) community DNA and soil chemistry analysis. Using model selection, we identified the strongest drivers of community turnover and diversity. We found that changes in soil salinity and pH were the greatest drivers of understory plant community turnover, while tree biomass was best predicted by inundation. For microbial communities, we observed complex interactions between salinity, pH, and inundation driving community turnover