Salinization is a pervasive environmental concern for both inland and coastal wetland ecosystems. Strong environmental filters such as increased salinity can influence the composition of bacterial communities. Shifts in community structure and associated biogeochemical cycles can change in potentially unpredictable ways. Increasing salinization can reduce historically freshwater wetland ecosystem functions leading to decreased inorganic nitrogen removal and carbon storage. Our goal is to examine how historically freshwater wetland bacterial communities will respond to increased salinization and to the influx of saltwater bacterial communities. With increased salinity, bacterial communities will shift due to the inability of freshwater species to quickly adapt to saline conditions and the success of saltwater microorganisms to outcompete freshwater taxa. We hypothesize that salinity induced physiological stress will lead to decreased taxonomic and phylogenetic diversity and carbon cycling functions. We expect that bacterial communities will differ in composition according to salinity and colonization of saltwater communities. To determine how salinity and dispersal of saltwater communities influenced bacterial community composition, diversity, and carbon cycling functions, we used an experimental mesocosm approach.
Results/Conclusions
We found that salinity, but not dispersal, reduced bacterial taxonomic (i.e., based on species identity and abundance) and phylogenetic (based on relatedness of species) diversity. In addition, community composition shifted along the experimental salinity gradient. The compositional shifts were associated with changes in carbon mineralization rates. These shifts were drive in part by a unique group of bacterial taxa, many of which were unable to be classified, represented each salinity environment. Examining how environmental filter and dispersal mechanisms influence bacterial community assembly has potential to enhance the management of coastal freshwater ecosystems to promote carbon storage for climate change mitigation.