Prokaryotic community diversity in the sediments of saline lagoons and its resistance to seasonal disturbances by water level cycles

Abstract

Purpose Apart from having high concentrations of salt, some natural saline wetlands also go through cyclical fluctuations in water level. They are frequently considered vulnerable habitats. In the last decades, the reduction of rainfall in many areas, coupled with fertilizer overuse, is transforming wetlands, especially in climates with a pronounced dry season. We studied a seasonally flooded saline wetland, and focused on the changes in the microbial communities. Methods High-throughput sequencing was used to explore the diversity and structure of the prokaryotic communities present in the surface sediments. A water and soil salinity gradient along different lagoons in the wetland complex was observed. Results Salinity affected both microbial richness and composition. The highest microbial richness was observed in lagoons with lower salinity. Statistical analysis suggests that the differences in community composition were associated with differences in salinity level, although an anthropic disturbance (increasing levels of soil organic matter, SOM) that was present predominantly in one lagoon also had a noticeable effect. Sorting of samples using beta diversity distances revealed that differences among communities were due to the distinct habitats, that is, a lagoon’s salinity and SOM, not water level cycles. Differences between flooded and dry-out seasons were also explored and the linear model showed that only a small number of OTUs (2.5%) had statistical differences between seasons. Conclusion Our findings will help in understanding the effects that both salinity and drying-out periods, which are increasing problems worldwide, may have on microbial communities and their resistance to seasonal fluctuations in water levels.