AUTHOR=Giannopoulos Georgios , Hartop Katherine R. , Brown Bonnie L. , Song Bongkeun , Elsgaard Lars , Franklin Rima B. 

TITLE=Trace Metal Availability Affects Greenhouse Gas Emissions and Microbial Functional Group Abundance in Freshwater Wetland Sediments

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.560861

DOI=10.3389/fmicb.2020.560861

ISSN=1664-302X

ABSTRACT=<p>We investigated the effects of trace metal additions on microbial nitrogen (N) and carbon (C) cycling using freshwater wetland sediment microcosms amended with micromolar concentrations of copper (Cu), molybdenum (Mo), iron (Fe), and all combinations thereof. In addition to monitoring inorganic N transformations (NO<sub>3</sub><sup>–</sup>, NO<sub>2</sub><sup>–</sup>, N<sub>2</sub>O, NH<sub>4</sub><sup>+</sup>) and carbon mineralization (CO<sub>2</sub>, CH<sub>4</sub>), we tracked changes in functional gene abundance associated with denitrification (<italic>nirS</italic>, <italic>nirK</italic>, <italic>nosZ</italic>), dissimilatory nitrate reduction to ammonium (DNRA; <italic>nrfA</italic>), and methanogenesis (<italic>mcrA</italic>). With regards to N cycling, greater availability of Cu led to more complete denitrification (i.e., less N<sub>2</sub>O accumulation) and a higher abundance of the <italic>nirK</italic> and <italic>nosZ</italic> genes, which encode for Cu-dependent reductases. In contrast, we found sparse biochemical evidence of DNRA activity and no consistent effect of the trace metal additions on <italic>nrfA</italic> gene abundance. With regards to C mineralization, CO<sub>2</sub> production was unaffected, but the amendments stimulated net CH<sub>4</sub> production and Mo additions led to increased <italic>mcrA</italic> gene abundance. These findings demonstrate that trace metal effects on sediment microbial physiology can impact community-level function. We observed direct and indirect effects on both N and C biogeochemistry that resulted in increased production of greenhouse gasses, which may have been mediated through the documented changes in microbial community composition and shifts in functional group abundance. Overall, this work supports a more nuanced consideration of metal effects on environmental microbial communities that recognizes the key role that metal limitation plays in microbial physiology.</p>