Diversity and activity of nitrogen‐fixing communities across ocean basins
By M. Gradoville, Deniz Bombar, B. Crump, Ricardo M Letelier, Jonathan P. Zehr, A. White. 2017
123 citations recorded by the source corpus.
Recent observations of N2 fixation rates (NFR) and the presence of nitrogenase (nifH) genes from heterotrophic N2‐fixing (diazotrophic) prokaryotes in unusual habitats challenge the paradigm that pelagic marine N2 fixation is constrained to cyanobacteria in warm, oligotrophic, surface waters. Here, we compare NFR and diazotrophic diversity (assessed via high‐throughput nifH sequencing) from a region known to be dominated by cyanobacterial diazotrophs (the North Pacific Subtropical Gyre, NPSG) to two regions dominated by heterotrophic diazotrophs: the Eastern South Pacific (ESP, from the Chilean upwelling system to the subtropical gyre) and the Pacific Northwest coastal upwelling system (PNW). We observed distinct biogeographical patterns among the three regions. Diazotrophic community structure differed strongly between the NPSG, dominated by cyanobacterium UCYN‐A, and the ESP, dominated by heterotrophic nifH group 1J/1K, yet surface NFR were similar in magnitude (up to 5.1 nmol N L−1 d−1). However, while diverse, predominantly heterotrophic nifH genes were recovered from the PNW and the mesopelagic of the NPSG, NFR were undetectable in both of these environments (although glucose amendments stimulated low rates in the deep NPSG). Our work suggests that while diazotrophs may be nearly omnipresent in marine waters, the activity of this functional group is regionally restricted. Further, we show that the detection limits of the 15N2 fixation assay suggest that many of the low NFR reported for the mesopelagic (often < 0.1 nmol N L−1 d−1 in the literature) are not indicative of active diazotrophy, highlighting the challenges of assessing the ecosystem significance of heterotrophic diazotrophs.
Subfields: Ecology, Oceanography, Pollution
View Paper: https://www.semanticscholar.org/paper/cde0d2b79384858e238526ebbac9058de5b1e223
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Citations in the corpus
- Diazotroph community structure and the role of nitrogen fixation in the nitrogen cycle in the Chukchi Sea (western Arctic Ocean) (2018, background): “…fixation, which is the reduction of atmospheric N2 to ammonia by diazotrophic microbes, is a major source of oceanic-fixed nitrogen, which supports new production (Karl et al. 1997; Shiozaki et al. 2009, 2017) and is eventually lost from marine ecosystems through denitrification (Gruber 2008).”