Abstract
Saltpans are a class of ephemeral wetland characterized by alternating periods of inundation, rising salinity, and desiccation. We obtained soil cores from a saltpan on the Mississippi Gulf coast in both the inundated and desiccated state. The microbiomes of surface and 30 cm deep sediment were determined using Illumina sequencing of the V4 region of the 16S rRNA gene. Bacterial and archaeal community composition differed significantly between sediment depths but did not differ between inundated and desiccated states. Well-represented taxa included marine microorganisms as well as multiple halophiles, both observed in greater proportions in surface sediment. Functional inference of metagenomic data showed that saltpan sediments in the inundated state had greater potential for microbial activity and that several energetic and degradation pathways were more prevalent in saltpan sediment than in nearby tidal marsh sediment. Microbial communities within saltpan sediments differed in composition from those in adjacent freshwater and brackish marshes. These findings indicate that the bacterial and archaeal microbiomes of saltpans are highly stratified by sediment depth and are only minimally influenced by changes in hydration. The surface sediment community is likely isolated from the shallow subsurface community by compaction, with the microbial community dominated by marine and terrestrial halophiles.
Highlights
Saltpans are a class of hypersaline wetland that are often intermixed with tidal freshwater, brackish, and saltwater marshes [1,2]
As saltwater intrusion progresses into tidal wetlands, it is projected that high salt marsh and salt flat wetland types will replace areas historically occupied by tidal freshwater, brackish, and salt marshes [2,7]
The replacement of tidal fresh, brackish, and salt marsh by upland salt marshes, saltpans, and other tidal flats underscores the importance of understanding the microbial community of these habitats, which are the primary drivers of carbon storage and nutrient cycling in those ecosystems [10,11,12]
Summary
Saltpans are a class of hypersaline wetland that are often intermixed with tidal freshwater, brackish, and saltwater marshes [1,2]. Saltpan formation can occur in high marsh plateaus and within shallow depressions of tidal marshes, where salts can become trapped and concentrate when water evaporates [2]. As saltwater intrusion progresses into tidal wetlands, it is projected that high salt marsh and salt flat wetland types will replace areas historically occupied by tidal freshwater, brackish, and salt marshes [2,7]. Each of these wetland types is conducive to the formation of saltpans. Microbial mediation of energy flows and nutrient cycles within wetlands has been well described [10,11,12], but it is, as yet, unclear whether microbial communities and processes in tidal flats and saltpans resemble those in vegetated, tidal wetlands
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