Marshes are particularly important ecosystems, providing long-term soil carbon storage, flood protection and nutrient filtration. Nutrient filtering, specifically nitrate removal, is largely the result of belowground microbially mediated denitrification. Previous studies reveal that denitrification rates differ in Spartina alterniflora and Juncus roemerianus patches but determining how the associated microbial communities contribute to these differences is challenged by the inherent physicochemical variability in the belowground of plants at different elevations in the marsh. Here we had a unique opportunity to evaluate denitrification rates and the belowground microbial community in J. roemerianus and S. alterniflora collocated at the same elevation, thus experiencing the same inundation cycles, in a saltwater marsh. To determine denitrification rates sediment slurry incubations (15N-nitrate) were used. The microbial community structure was determined using “iTag” sequencing of 16S rRNA gene amplicons. Slurry experiments revealed that denitrification rates were consistently higher in J. roemerianus compared to S. alterniflora. Analysis of 16S rRNA exact amplicon sequence variants (ASVs) showed that the microbial communities were similar in both plant types, although oscillations in the abundance of some ASVs was observed. To link the rate and microbial community data, Random Forest Modeling (RFM) was used to determine if specific microbes could be accurate predictors of higher or lower denitrification rates. RFM identified ASVs classified as Deltaproteobacteria; Desulfobacteraceae and Chloroflexi; Anaerolineaceae as the most important predictors of denitrification rates. These microbial predictors were also identified as core members of the rhizosphere of both plants. The Desulfobacteraceae core member, indicates higher denitrification rates, while the Anaerolineaceae core member points towards lower rates of nitrate removal. Desulfobacteraceae are known sulfate reducers, however some have been shown to utilize both nitrate and sulfate to grow chemolithoautotrophically by coupling sulfide oxidation to dissimilatory nitrate reduction. In fact, this pathway was identified in metagenomic and metatranscriptomic datasets from one of the samples analyzed herein. Collectively, our data revealed that J. roemerianus promoted greater belowground nitrate removal compared to S. alterniflora which may result from different plant characteristics that lead to oscillations in the abundance and activity of core members of the microbial community that can serve as predictors of denitrification rates. Further, the data suggested that this reaction may be mediated by previously unsuspected sulfate reducing bacteria in our saltmarsh ecosystem. / A Thesis submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester 2019. / March 28, 2019. / Includes bibliographical references. / Olivia Mason, Professor Directing Thesis; Angela Knapp, Committee Member; Sven Kranz, Committee Member; Brian Chadwick, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_709320 |
| Contributors | Petet, Rachel Anne (author), Mason, Olivia Underwood (Professor Directing Thesis), Knapp, Angela Noel (Committee Member), Kranz, Sven Alexander (Committee Member), Chadwick, Brian P. (Committee Member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Earth, Ocean and Atmospheric Science (degree granting departmentdgg) |
| Publisher | Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text, master thesis |
| Format | 1 online resource (33 pages), computer, application/pdf |
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