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<p class="HTMLBody" align="center" style="text-align:center;line-height:115%"><b><u><span style="font-size:26.0pt;line-height:115%;font-family:"Monotype Corsiva"">Oceanography Seminar</span></u></b><o:p></o:p></p>
<p class="HTMLBody" align="center" style="text-align:center;line-height:115%"><b><span style="font-size:28.0pt;line-height:115%;font-family:"Monotype Corsiva"">Rachel Petet</span></b><o:p></o:p></p>
<p class="HTMLBody" align="center" style="text-align:center"><span style="font-size:28.0pt;font-family:"Monotype Corsiva"">M.S. Biological Oceanography Candidate</span><o:p></o:p></p>
<p class="HTMLBody"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="doublespacedcaps"><b><u><span style="font-size:14.0pt;line-height:200%">Title</span></u>:</b> Impacts of microbial community structure on denitrification rates in the rhizosphere of
<i>J. roemerianus</i> and <i>S. alterniflora</i> collocated in a Gulf of Mexico saltwater marsh<o:p></o:p></p>
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<p class="MsoNormal"><b><u><span style="font-size:14.0pt">Major Professor</span></u></b><b><span style="font-size:14.0pt">: Dr. Olivia U. Mason</span></b><o:p></o:p></p>
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<p class="MsoNormal"><b><u><span style="font-size:14.0pt">Date</span></u></b><b><span style="font-size:14.0pt">:</span></b><span style="font-size:14.0pt"> March 28<sup>rd</sup>, 2019
<b><u>Time</u>: 10:00 AM</b></span><o:p></o:p></p>
<p class="HTMLBody"><b> </b><o:p></o:p></p>
<p class="HTMLBody"><b><u><span style="font-size:14.0pt">Location</span></u></b><b><span style="font-size:14.0pt">:
</span></b><span style="font-size:14.0pt">Chemistry 1005 (CSL 1005)</span><o:p></o:p></p>
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<p class="MsoNormal" align="center" style="text-align:center"><b>ABSTRACT</b><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New Roman",serif">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. Denitrification rates differ in
<i>Spartina alterniflora </i>and <i>Juncus roemerianus</i> 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
<i>J. roemerianus</i> and <i>S. alterniflora</i> collocated at the same elevation, thus experiencing the same inundation cycles, in a saltwater marsh. To determine denitrification rates sediment slurry incubations (<sup>15</sup>N-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
<i>J. roemerianus</i>. Analysis of 16S rRNA exact amplicon sequence variants (ASVs) showed that the microbial communities were similar in both plant types, although significant oscillations in 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;
<i>Desulfobacteraceae</i> and Chloroflexi; <i>Anaerolineaceae</i> as the most important predictors of denitrification rates. These microbial predictors were also identified as core members of the rhizosphere of both plants.
<i>Desulfobacteraceae</i>, indicates higher denitrification rates, while <i>Anaerolineaceae</i> points towards lower rates of nitrate removal.
<i>Desulfobacteraceae</i> 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
a complimentary metagenomic dataset. Collectively, our data revealed that <i>J. roemerianus</i> promoted greater belowground nitrate removal compared to
<i>S. alterniflora</i> which may result from different plant characteristics that lead to oscillations in the abundance of core members of the microbial community that can serve as predictors of denitrification rates and that this reaction may be mediated by
previously unsuspected sulfate reducing bacteria in our saltmarsh ecosystem</span><o:p></o:p></p>
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