Electronic Theses and Dissertations

Date of Award

1-1-2021

Document Type

Dissertation

Degree Name

Ph.D. in Biological Science

First Advisor

Colin R. Jackson

Second Advisor

James Cizdziel

Third Advisor

Patrick Curtis

Relational Format

dissertation/thesis

Abstract

Sediment microbial community responses to elevated salinity are important in predicting the effects of sea level rise as well as in understanding those communities that can thrive in extreme environments. In this dissertation, I use natural and field experiments to investigate how salinity influences microbiome structure in coastal wetlands. Through the use of amplicon sequencing, I demonstrate that there are compositional differences between the microbiota of four wetland salinity classes: limnetic, oligohaline, mesohaline, and polyhaline. These results were reciprocated in a microcosm study exposing freshwater sediment to meso- and polyhaline conditions, showing that communities shifted proportionally to the magnitude of salinity added. Through assays of the activity of extracellular enzymes responsible for the degradation of organic matter, decomposition rates were inferred to be higher in fresher marsh types across both field and microcosm data. These results suggest that greater carbon storage in saltmarshes may enable those marshes to accrue more sediment than freshwater marsh, allowing them to keep pace with sea levels, potentially expanding saltmarsh area relative to fresh marsh. In contrast to gradual salinification due to sea level rise, acute marsh inundation from tropical cyclone events was also explored. Microbial community composition and activity were disrupted immediately following storms, but recovered within one month, demonstrating that storm surge alone is unlikely to shift wetland salinity regimes permanently. The microbiome of a saltpan, with salinities regularly higher than seawater was also explored as a model for extremes of desiccation and osmotic stress. Understanding community tolerance of hypersalinity is important in the search for life in extreme environments, even those encountered on Mars. I show that multiple species from the saltpan community were able to survive Mars-relevant conditions, although the addition of perchlorate salts that are prevalent on Mars was deleterious for growth. I demonstrate that there are large compositional and functional differences between the microbiomes of wetlands across large salinity gradients, from fresh to hypersaline. Characterization of these differences will be important in predicting future coastal land cover, carbon storage, nutrient cycling, and in understanding the boundaries of environmental habitability.

Available for download on Wednesday, December 14, 2022

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