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1. Global oceanic diazotroph database version 2 and elevated estimate of global oceanic N2 fixation

Author

Shao, Zhibo, Xu, Yangchun, Wang, Hua, Luo, Weicheng, Wang, Lice, Huang, Yuhong, Agawin, Nona Sheila R, Ahmed, Ayaz, Benavides, Mar, Bentzon-Tilia, Mikkel, Berman-Frank, Ilana, Berthelot, Hugo, Biegala, Isabelle C, Bif, Mariana B, Bode, Antonio, Bonnet, Sophie, Bronk, Deborah A, Brown, Mark V, Campbell, Lisa, Capone, Douglas G, Carpenter, Edward J, Cassar, Nicolas, Chang, Bonnie X, Chappell, Dreux, Chen, Yuh-ling Lee, Church, Matthew J, Cornejo-Castillo, Francisco M, Detoni, Amália Maria Sacilotto, Doney, Scott C, Dupouy, Cecile, Estrada, Marta, Fernandez, Camila, Fernández-Castro, Bieito, Fonseca-Batista, Debany, Foster, Rachel A, Furuya, Ken, Garcia, Nicole, Goto, Kanji, Gago, Jesús, Gradoville, Mary R, Hamersley, M Robert, Henke, Britt A, Hörstmann, Cora, Jayakumar, Amal, Jiang, Zhibing, Kao, Shuh-Ji, Karl, David M, Kittu, Leila R, Knapp, Angela N, Kumar, Sanjeev, LaRoche, Julie, Liu, Hongbin, Liu, Jiaxing, Lory, Caroline, Löscher, Carolin R, Marañón, Emilio, Messer, Lauren F, Mills, Matthew M, Mohr, Wiebke, Moisander, Pia H, Mahaffey, Claire, Moore, Robert, Mouriño-Carballido, Beatriz, Mulholland, Margaret R, Nakaoka, Shin-ichiro, Needoba, Joseph A, Raes, Eric J, Rahav, Eyal, Ramírez-Cárdenas, Teodoro, Reeder, Christian Furbo, Riemann, Lasse, Riou, Virginie, Robidart, Julie C, Sarma, Vedula VSS, Sato, Takuya, Saxena, Himanshu, Selden, Corday, Seymour, Justin R, Shi, Dalin, Shiozaki, Takuhei, Singh, Arvind, Sipler, Rachel E, Sun, Jun, Suzuki, Koji, Takahashi, Kazutaka, Tan, Yehui, Tang, Weiyi, Tremblay, Jean-Éric, Turk-Kubo, Kendra, Wen, Zuozhu, White, Angelicque E, Wilson, Samuel T, Yoshida, Takashi, Zehr, Jonathan P, Zhang, Run, Zhang, Yao, and Luo, Ya-Wei

Subjects
Life Below Water, Atmospheric Sciences, Geochemistry, Physical Geography and Environmental Geoscience
Abstract

Abstract. Marine diazotrophs convert dinitrogen (N2) gas intobioavailable nitrogen (N), supporting life in the global ocean. In 2012, thefirst version of the global oceanic diazotroph database (version 1) waspublished. Here, we present an updated version of the database (version 2),significantly increasing the number of in situ diazotrophic measurements from13 565 to 55 286. Data points for N2 fixation rates, diazotrophic cellabundance, and nifH gene copy abundance have increased by 184 %, 86 %, and809 %, respectively. Version 2 includes two new data sheets for the nifH genecopy abundance of non-cyanobacterial diazotrophs and cell-specific N2fixation rates. The measurements of N2 fixation rates approximatelyfollow a log-normal distribution in both version 1 and version 2. However,version 2 considerably extends both the left and right tails of thedistribution. Consequently, when estimating global oceanic N2 fixationrates using the geometric means of different ocean basins, version 1 andversion 2 yield similar rates (43–57 versus 45–63 Tg N yr−1; rangesbased on one geometric standard error). In contrast, when using arithmeticmeans, version 2 suggests a significantly higher rate of 223±30 Tg N yr−1 (mean ± standard error; same hereafter) compared to version 1(74±7 Tg N yr−1). Specifically, substantial rate increases areestimated for the South Pacific Ocean (88±23 versus 20±2 Tg N yr−1), primarily driven by measurements in the southwestern subtropics,and for the North Atlantic Ocean (40±9 versus 10±2 Tg N yr−1). Moreover, version 2 estimates the N2 fixation rate in theIndian Ocean to be 35±14 Tg N yr−1, which could not be estimatedusing version 1 due to limited data availability. Furthermore, a comparisonof N2 fixation rates obtained through different measurement methods atthe same months, locations, and depths reveals that the conventional15N2 bubble method yields lower rates in 69 % cases compared tothe new 15N2 dissolution method. This updated version of thedatabase can facilitate future studies in marine ecology andbiogeochemistry. The database is stored at the Figshare repository(https://doi.org/10.6084/m9.figshare.21677687; Shao etal., 2022).

Published
2023

3. Gammaproteobacterial diazotrophs and nifH gene expression in surface waters of the South Pacific Ocean

Author

Moisander, Pia H, Serros, Tracy, Paerl, Ryan W, Beinart, Roxanne A, and Zehr, Jonathan P

Subjects
Genetics, Life Below Water, Cyanobacteria, Gammaproteobacteria, Gene Dosage, Gene Expression, Nitrogen Fixation, Oxidoreductases, Pacific Ocean, Phylogeny, Seawater, Temperature, Water Microbiology, Crocosphaera, diel cycle, nifH, nitrogen cycle, transcription, UCYN-A, Environmental Sciences, Biological Sciences, Technology, Microbiology
Abstract

In addition to the cyanobacterial N2-fixers (diazotrophs), there is a high nifH gene diversity of non-cyanobacterial groups present in marine environments, yet quantitative information about these groups is scarce. N2 fixation potential (nifH gene expression), diversity and distributions of the uncultivated diazotroph phylotype γ-24774A11, a putative gammaproteobacterium, were investigated in the western South Pacific Ocean. γ-24774A11 gene copies correlated positively with diazotrophic cyanobacteria, temperature, dissolved organic carbon and ambient O2 saturation, and negatively with depth, chlorophyll a and nutrients, suggesting that carbon supply, access to light or inhibitory effects of DIN may control γ-24774A11 abundances. Maximum nifH gene-copy abundance was 2 × 10(4) l(-1), two orders of magnitude less than that for diazotrophic cyanobacteria, while the median γ-24774A11 abundance, 8 × 10(2) l(-1), was greater than that for the UCYN-A cyanobacteria, suggesting a more homogeneous distribution in surface waters. The abundance of nifH transcripts by γ-24774A11 was greater during the night than during the day, and the transcripts generally ranged from 0-7%, but were up to 26% of all nifH transcripts at each station. The ubiquitous presence and low variability of γ-24774A11 abundances across tropical and subtropical oceans, combined with the consistent nifH expression reported in this study, suggest that γ-24774A11 could be one of the most important heterotrophic (or photoheterotrophic) diazotrophs and may need to be considered in future N budget estimates and models.

Published
2014

10. Supplement of Global oceanic diazotroph database version 2 and elevated estimate of global oceanic N2 fixation

Author

Ya-Wei Luo [ywluo@xmu.edu.cn], Shao, Zhibo, Xu, Yangchun, Wuang, Hua, Luo, Weicheng, Wuang, Lice, Huang, Yuhong, Agawin, Nona S. R., Ahmed, Ayad, Benavides, Mar, Bentzon-Tilia, Mikkel, Berman-Frank, Ilana, Berthelot, Hugo, Biegala, Isabelle C., Vif, Mariana B., Bode, Antonio, Bonnet, Sophie, Bronk, Deborah A., Brown, Mark V., Campbell, Lisa, Capone, Douglas G., Carpenter, Edward J., Cassar, Nicolas, Chang, Bonnie X., Chappell, Dreux, Lee Chen, Yuh-ling, Church, Matthew J., Cornejo-Castillo, Francisco M., Sacilotto Detoni, Amália Maria, Doney, Scott C., Dupouy, Cecile, Estrada, Marta, Fernández, Camila, Fernández-Castro, Bieito, Fonseca-Batista, Debany, Foster, Rachel A., Furuya, Ken, García, Nicole, Goto, Kanji, Gago, Jesús, Gradoville, Mary R., Hamersley, M. Robert, Henke, Britt A., Hörstmann, Cora, Jayakumar, Amal, Jiang, Zhibing, Kao, Shu-Ji, Karl, David M., Kittu, Leila R., Knapp, Angela N., Kumar, Sanjeeb, LaRoche, Julie, Liu, Hongbin, Liu, Jiaxing, Lory, Caroline, Löscher, Carolin R., Marañón, Emilio, Messer, Lauren F., Mills, Matthew M., Mohr, Miebke, Moisander, Pia H., Mahaffey, Claire, Moore, Robert, Mouriño-Carballido, Beatriz, Mulholland, Margaret R., Nakaoka, Shin-Ichiro, Needoba, Joseph A., Raes, Eric J., Rahav, Eyal, Ramírez-Cárdenas, Teodoro, Furbo Reeder, Christian, Riemann, Lasse, Riou, Virginie, Robidart, Julie C., Sarma, Vedula V. S. S., Sato, Takuya, Saxena, Himanshu, Selden, Corday, Seymour, Justin R., Shi, Dalin, Shiozaki, Takuhei, Singh, Arvind, Sipler, Rachel E., Sun, Jun, Suzuki, Koji, Takahashi, Kazutaka, Tan, Yehui, Tang, Weiyi, Tremblay, Jean-Éric, Turk-Kubo, Kendra, Wen, Zuozhu, White, Angelicque E., Wilson, Samuel T., Yoshida, Takashi, Zehr, Jonathan P., Zhang, Run, Zhang, Yao, Luo, Ya-Wei, Ya-Wei Luo [ywluo@xmu.edu.cn], Shao, Zhibo, Xu, Yangchun, Wuang, Hua, Luo, Weicheng, Wuang, Lice, Huang, Yuhong, Agawin, Nona S. R., Ahmed, Ayad, Benavides, Mar, Bentzon-Tilia, Mikkel, Berman-Frank, Ilana, Berthelot, Hugo, Biegala, Isabelle C., Vif, Mariana B., Bode, Antonio, Bonnet, Sophie, Bronk, Deborah A., Brown, Mark V., Campbell, Lisa, Capone, Douglas G., Carpenter, Edward J., Cassar, Nicolas, Chang, Bonnie X., Chappell, Dreux, Lee Chen, Yuh-ling, Church, Matthew J., Cornejo-Castillo, Francisco M., Sacilotto Detoni, Amália Maria, Doney, Scott C., Dupouy, Cecile, Estrada, Marta, Fernández, Camila, Fernández-Castro, Bieito, Fonseca-Batista, Debany, Foster, Rachel A., Furuya, Ken, García, Nicole, Goto, Kanji, Gago, Jesús, Gradoville, Mary R., Hamersley, M. Robert, Henke, Britt A., Hörstmann, Cora, Jayakumar, Amal, Jiang, Zhibing, Kao, Shu-Ji, Karl, David M., Kittu, Leila R., Knapp, Angela N., Kumar, Sanjeeb, LaRoche, Julie, Liu, Hongbin, Liu, Jiaxing, Lory, Caroline, Löscher, Carolin R., Marañón, Emilio, Messer, Lauren F., Mills, Matthew M., Mohr, Miebke, Moisander, Pia H., Mahaffey, Claire, Moore, Robert, Mouriño-Carballido, Beatriz, Mulholland, Margaret R., Nakaoka, Shin-Ichiro, Needoba, Joseph A., Raes, Eric J., Rahav, Eyal, Ramírez-Cárdenas, Teodoro, Furbo Reeder, Christian, Riemann, Lasse, Riou, Virginie, Robidart, Julie C., Sarma, Vedula V. S. S., Sato, Takuya, Saxena, Himanshu, Selden, Corday, Seymour, Justin R., Shi, Dalin, Shiozaki, Takuhei, Singh, Arvind, Sipler, Rachel E., Sun, Jun, Suzuki, Koji, Takahashi, Kazutaka, Tan, Yehui, Tang, Weiyi, Tremblay, Jean-Éric, Turk-Kubo, Kendra, Wen, Zuozhu, White, Angelicque E., Wilson, Samuel T., Yoshida, Takashi, Zehr, Jonathan P., Zhang, Run, Zhang, Yao, and Luo, Ya-Wei

Published
2023

11. Global oceanic diazotroph database version 2 and elevated estimate of global oceanic N2 fixation

Author

National Natural Science Foundation of China, Agencia Estatal de Investigación (España), Shao, Zhibo, Xu, Yangchun, Wuang, Hua, Luo, Weicheng, Wuang, Lice, Huang, Yuhong, Agawin, Nona S. R., Ahmed, Ayad, Benavides, Mar, Bentzon-Tilia, Mikkel, Berman-Frank, Ilana, Berthelot, Hugo, Biegala, Isabelle C., Vif, Mariana B., Bode, Antonio, Bonnet, Sophie, Bronk, Deborah A., Brown, Mark V., Campbell, Lisa, Capone, Douglas G., Carpenter, Edward J., Cassar, Nicolas, Chang, Bonnie X., Chappell, Dreux, Lee Chen, Yuh-ling, Church, Matthew J., Cornejo-Castillo, Francisco M., Sacilotto Detoni, Amália Maria, Doney, Scott C., Dupouy, Cecile, Estrada, Marta, Fernández, Camila, Fernández-Castro, Bieito, Fonseca-Batista, Debany, Foster, Rachel A., Furuya, Ken, García, Nicole, Goto, Kanji, Gago, Jesús, Gradoville, Mary R., Hamersley, M. Robert, Henke, Britt A., Hörstmann, Cora, Jayakumar, Amal, Jiang, Zhibing, Kao, Shu-Ji, Karl, David M., Kittu, Leila R., Knapp, Angela N., Kumar, Sanjeeb, LaRoche, Julie, Liu, Hongbin, Liu, Jiaxing, Lory, Caroline, Löscher, Carolin R., Marañón, Emilio, Messer, Lauren F., Mills, Matthew M., Mohr, Miebke, Moisander, Pia H., Mahaffey, Claire, Moore, Robert, Mouriño-Carballido, Beatriz, Mulholland, Margaret R., Nakaoka, Shin-Ichiro, Needoba, Joseph A., Raes, Eric J., Rahav, Eyal, Ramírez-Cárdenas, Teodoro, Furbo Reeder, Christian, Riemann, Lasse, Riou, Virginie, Robidart, Julie C., Sarma, Vedula V. S. S., Sato, Takuya, Saxena, Himanshu, Selden, Corday, Seymour, Justin R., Shi, Dalin, Shiozaki, Takuhei, Singh, Arvind, Sipler, Rachel E., Sun, Jun, Suzuki, Koji, Takahashi, Kazutaka, Tan, Yehui, Tang, Weiyi, Tremblay, Jean-Éric, Turk-Kubo, Kendra, Wen, Zuozhu, White, Angelicque E., Wilson, Samuel T., Yoshida, Takashi, Zehr, Jonathan P., Zhang, Run, Zhang, Yao, Luo, Ya-Wei, National Natural Science Foundation of China, Agencia Estatal de Investigación (España), Shao, Zhibo, Xu, Yangchun, Wuang, Hua, Luo, Weicheng, Wuang, Lice, Huang, Yuhong, Agawin, Nona S. R., Ahmed, Ayad, Benavides, Mar, Bentzon-Tilia, Mikkel, Berman-Frank, Ilana, Berthelot, Hugo, Biegala, Isabelle C., Vif, Mariana B., Bode, Antonio, Bonnet, Sophie, Bronk, Deborah A., Brown, Mark V., Campbell, Lisa, Capone, Douglas G., Carpenter, Edward J., Cassar, Nicolas, Chang, Bonnie X., Chappell, Dreux, Lee Chen, Yuh-ling, Church, Matthew J., Cornejo-Castillo, Francisco M., Sacilotto Detoni, Amália Maria, Doney, Scott C., Dupouy, Cecile, Estrada, Marta, Fernández, Camila, Fernández-Castro, Bieito, Fonseca-Batista, Debany, Foster, Rachel A., Furuya, Ken, García, Nicole, Goto, Kanji, Gago, Jesús, Gradoville, Mary R., Hamersley, M. Robert, Henke, Britt A., Hörstmann, Cora, Jayakumar, Amal, Jiang, Zhibing, Kao, Shu-Ji, Karl, David M., Kittu, Leila R., Knapp, Angela N., Kumar, Sanjeeb, LaRoche, Julie, Liu, Hongbin, Liu, Jiaxing, Lory, Caroline, Löscher, Carolin R., Marañón, Emilio, Messer, Lauren F., Mills, Matthew M., Mohr, Miebke, Moisander, Pia H., Mahaffey, Claire, Moore, Robert, Mouriño-Carballido, Beatriz, Mulholland, Margaret R., Nakaoka, Shin-Ichiro, Needoba, Joseph A., Raes, Eric J., Rahav, Eyal, Ramírez-Cárdenas, Teodoro, Furbo Reeder, Christian, Riemann, Lasse, Riou, Virginie, Robidart, Julie C., Sarma, Vedula V. S. S., Sato, Takuya, Saxena, Himanshu, Selden, Corday, Seymour, Justin R., Shi, Dalin, Shiozaki, Takuhei, Singh, Arvind, Sipler, Rachel E., Sun, Jun, Suzuki, Koji, Takahashi, Kazutaka, Tan, Yehui, Tang, Weiyi, Tremblay, Jean-Éric, Turk-Kubo, Kendra, Wen, Zuozhu, White, Angelicque E., Wilson, Samuel T., Yoshida, Takashi, Zehr, Jonathan P., Zhang, Run, Zhang, Yao, and Luo, Ya-Wei

Abstract

Marine diazotrophs convert dinitrogen (N2) gas into bioavailable nitrogen (N), supporting life in the global ocean. In 2012, the first version of the global oceanic diazotroph database (version 1) was published. Here, we present an updated version of the database (version 2), significantly increasing the number of in situ diazotrophic measurements from 13 565 to 55 286. Data points for N2 fixation rates, diazotrophic cell abundance, and nifH gene copy abundance have increased by 184 %, 86 %, and 809 %, respectively. Version 2 includes two new data sheets for the nifH gene copy abundance of non-cyanobacterial diazotrophs and cell-specific N2 fixation rates. The measurements of N2 fixation rates approximately follow a log-normal distribution in both version 1 and version 2. However, version 2 considerably extends both the left and right tails of the distribution. Consequently, when estimating global oceanic N2 fixation rates using the geometric means of different ocean basins, version 1 and version 2 yield similar rates (43–57 versus 45–63 Tg N yr−1 ; ranges based on one geometric standard error). In contrast, when using arithmetic means, version 2 suggests a significantly higher rate of 223±30 Tg N yr−1(mean ± standard error; same hereafter) compared to version 1 (74 ± 7 Tg N yr−1). Specifically, substantial rate increases are estimated for the South Pacific Ocean (88±23 versus 20±2 Tg N yr−1), primarily driven by measurements in the southwestern subtropics, and for the North Atlantic Ocean (40 ± 9 versus 10 ±2 Tg N yr−1). Moreover, version 2 estimates the N2 fixation rate in the Indian Ocean to be 35 ± 14 Tg N yr−1,which could not be estimated using version 1 due to limited data availability. Furthermore, a comparison of N2 fixation rates obtained through different measurement methods at the same months, locations, and depths reveals that the conventional 15N2 bubble method yields lower rates in 69 % cases compared to the new 15N2 dissolution method. This updated ve

Published
2023

14. Constraining uncertainties of diazotroph biogeography from nifH gene abundance

Author

Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Meiler, Simona, Britten, Gregory L, Dutkiewicz, Stephanie, Gradoville, Mary Rose, Moisander, Pia H, Jahn, Oliver, Follows, Michael J, Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences, Meiler, Simona, Britten, Gregory L, Dutkiewicz, Stephanie, Gradoville, Mary Rose, Moisander, Pia H, Jahn, Oliver, and Follows, Michael J

Published
2022

30. Dissolved organic matter stimulates N₂ fixation and nifH gene expression in Trichodesmium

Author

Benavides, Mar, Duhamel, Solange, Van Wambeke, France, Shoemaker, Katyanne M., Moisander, Pia H., Salamon, Ellen, Riemann, Lasse, and Bonnet, Sophie

Subjects
Trichodesmium, Marine plankton, Marine microbiology, Biogeochemistry, Nitrogen--Fixation
Abstract

Mixotrophy, the combination of heterotrophic and autotrophic nutrition modes, is emerging as the rule rather than the exception in marine photosynthetic plankton. Trichodesmium, a prominent diazotroph ubiquitous in the (sub)tropical oceans, is generally considered to obtain energy via autotrophy. While the ability of Trichodesmium to use dissolved organic phosphorus when deprived of inorganic phosphorus sources is well known, the extent to which this important cyanobacterium may benefit from other dissolved organic matter (DOM) sources is unknown. Here we provide evidence of carbon-, nitrogen- and phosphorus-rich DOM molecules enhancing N₂ fixation rates and nifH gene expression in natural Trichodesmium colonies collected at two stations in the western tropical South Pacific. Sampling at a third station located in the oligotrophic South Pacific Gyre revealed no Trichodesmium but showed presence of UCYN-B, although no nifH expression was detected. Our results suggest that Trichodesmium may behave mixotrophically in response to certain environmental conditions, providing them with metabolic plasticity and adding up to the view that mixotrophy is widespread among marine microbes.

Published
2020
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31. High N2 Fixation in and Near the Gulf Stream Consistent with a Circulation Control on Diazotrophy

Author

Palter, Jaime B., Ames, Elana J, Benavides, Mar, Goncalves Neto, Afonso, Granger, Julie, Moisander, Pia H, Watkins-Brandt, Katie S, White, Angelicque E, Palter, Jaime B., Ames, Elana J, Benavides, Mar, Goncalves Neto, Afonso, Granger, Julie, Moisander, Pia H, Watkins-Brandt, Katie S, and White, Angelicque E

Abstract

The stoichiometry of physical nutrient supply may provide a constraint on the spatial distribution and rate of marine nitrogen (N2) fixation. Yet agreement between the N2 fixation rates inferred from nutrient supply and those directly measured has been lacking. The relative transport of phosphate and nitrate across the Gulf Stream suggests that 3–6 Tg N year−1 must be fixed to maintain steady nutrient stoichiometry in the North Atlantic subtropical gyre. Here we show direct measurements of N2 fixation consistent with these estimates, suggesting elevated N2 fixation in and near the Gulf Stream. At some locations across the Gulf Stream, we measured diazotroph abundances and N2 fixation rates that are 1–3 orders of magnitude greater than previously measured in the central North Atlantic subtropical gyre. In combination, rate measurements and gene abundances suggest that biogeochemical budgets can be a robust predictive tool for N2 fixation hot spots in the global ocean.

Published
2020

36. A critical review of the 15 N 2 tracer method to measure diazotrophic production in pelagic ecosystems

Author

White, Angelicque E., primary, Granger, Julie, additional, Selden, Corday, additional, Gradoville, Mary R., additional, Potts, Lindsey, additional, Bourbonnais, Annie, additional, Fulweiler, Robinson W., additional, Knapp, Angela N., additional, Mohr, Wiebke, additional, Moisander, Pia H., additional, Tobias, Craig R., additional, Caffin, Mathieu, additional, Wilson, Samuel T., additional, Benavides, Mar, additional, Bonnet, Sophie, additional, Mulholland, Margaret R., additional, and Chang, Bonnie X., additional

Published
2020
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40. Pelagic N2 fixation dominated by sediment diazotrophic communities in a shallow temperate estuary.

Author

Hallstrøm, Søren, Benavides, Mar, Salamon, Ellen R., Evans, Clayton W., Potts, Lindsey J., Granger, Julie, Tobias, Craig R., Moisander, Pia H., and Riemann, Lasse

Subjects
NITROGEN fixation, SEA level, ESTUARINE sediments, ESTUARY management, NUTRIENT cycles, ESTUARIES
Abstract

Estuaries receive substantial anthropogenic nitrogen loading and are mainly considered net nitrogen sinks. While several studies have identified diverse diazotrophic communities in estuarine sediments, the role of pelagic diazotrophs in these systems is not well understood. We investigated the links between diazotrophic community composition, nitrogenase (nifH) gene expression, N2 fixation, and environmental conditions in Narragansett Bay (USA). Pelagic N2 fixation rates ranged between 0.02 and 9.41 nmol N L−1 d−1 and correlated significantly with fluctuations in diazotroph community composition. These fluctuations were also correlated with temperature, salinity, and mean sea level. The dominant sequences in our pelagic samples were related to sequences previously detected in the bay's sediments and were dominated by nifH gene Clusters I and III. We interpret this as a coupling between sediment and pelagic diazotroph communities and speculate that resuspension plays an important role for pelagic N2 fixation in shallow estuarine environments such as Narragansett Bay. For instance, the finding of active sulfate reducers in the oxygenated water illustrates that the sediment‐pelagic coupling can impact nutrient cycling in shallow environments. The pelagic N2 fixation measured during our study period showed only a minor contribution (< 1%) to the total estimated nitrogen load to Narragansett Bay. However, with intensifying nitrogen management in estuaries, the need to constrain the rates of pelagic N2 fixation in these systems will be essential for estimating nitrogen fluxes within the bay and to the adjacent coastal ecosystems. [ABSTRACT FROM AUTHOR]

Published
2022
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44. Constraining uncertainties of diazotroph biogeography from nifHgene abundance

Author

Meiler, Simona, Britten, Gregory L., Dutkiewicz, Stephanie, Gradoville, Mary Rose, Moisander, Pia H., Jahn, Oliver, and Follows, Michael J.

Abstract

Marine diazotrophs fix dinitrogen gas into bioavailable nitrogen that drives the ocean nitrogen cycle; yet, efforts to infer global diazotroph distributions have been limited by a sparsity of observations. In situ measurements of nifHgene abundance (essential for nitrogen fixation) are increasingly being used to inform the biogeography of diazotrophs. However, comparing such gene abundances spatially, temporally and between diazotroph species remains difficult. We synthesize existing data on gene‐to‐cell and cell‐to‐biomass conversions for four major diazotroph groups to convert nifHgene counts to abundance‐ and biomass‐based biogeographic “currencies.” Results suggest up to two orders of magnitude uncertainty converting from nifHgene abundance to cell abundance, and up to four orders of magnitude uncertainty from nifHgene abundance to biomass. Uncertainty arises due to large taxonomic variation in cell size and presumed polyploidy, that is, variability in the number of genomes per cell. Such uncertainties hinder comparing biogeographies of different species. Additionally, numerical models need biogeographies for validation, typically in the currency of carbon biomass. Here, we show that conversion uncertainty from nifHgene abundance to biomass overwhelms biomass variability simulated in such models. These results demonstrate a basic currency problem in converting gene abundance observations to biogeographically meaningful quantities for synthesizing studies and modeling approaches. Such issues may also have relevance to other genes and organisms beyond diazotrophs. To avoid biases in interpreting gene counts as a measure of abundance, we suggest converting gene counts to a binary presence/non‐detect metric to map broad biogeographical distributions more robustly.

Published
2022
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46. Aphotic N2 fixation along an oligotrophic to ultraoligotrophic transect in the western tropical South Pacific Ocean

Author

Benavides, Mar, Shoemaker, Katyanne, Moisander, Pia H., Niggemann, Jutta, Dittmar, Thorsten, Duhamel, Solange, Grosso, Olivier, Pujo-Pay, Mireille, Helias Nunige, Sandra, Fumenia, Alain, Bonnet, Sophie, Institut méditerranéen d'océanologie (MIO), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Toulon (UTLN), University of Copenhagen = Københavns Universitet (KU), Lamont-Doherty Earth Observatory (LDEO), Columbia University [New York], Laboratoire d'Océanographie Microbienne (LOMIC), Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Observatoire océanologique de Banyuls (OOB), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut méditerranéen d'océanologie ( MIO ), Centre National de la Recherche Scientifique ( CNRS ) -Université de Toulon ( UTLN ) -Aix Marseille Université ( AMU ) -Institut de Recherche pour le Développement ( IRD ), University of Copenhagen ( KU ), Lamont-Doherty Earth Observatory ( LDEO ), Laboratoire d'Océanographie Microbienne ( LOMIC ), Université Pierre et Marie Curie - Paris 6 ( UPMC ) -Centre National de la Recherche Scientifique ( CNRS ), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Toulon (UTLN)-Centre National de la Recherche Scientifique (CNRS), University of Copenhagen = Københavns Universitet (UCPH), Observatoire océanologique de Banyuls (OOB), and Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[ SDU.STU.OC ] Sciences of the Universe [physics]/Earth Sciences/Oceanography, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography
Abstract

The western tropical South Pacific (WTSP) Ocean has been recognized as a global hot spot of dinitrogen (N2) fixation. Here, as in other marine environments across the oceans, N2 fixation studies have focused on the sunlit layer. However, studies have confirmed the importance of aphotic N2 fixation activity, although until now only one had been performed in the WTSP. In order to increase our knowledge of aphotic N2 fixation in the WTSP, we measured N2 fixation rates and identified diazotrophic phylotypes in the mesopelagic layer along a transect spanning from New Caledonia to French Polynesia. Because non-cyanobacterial diazotrophs presumably need external dissolved organic matter (DOM) sources for their nutrition, we also identified DOM compounds using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) with the aim of searching for relationships between the composition of DOM and non-cyanobacterial N2 fixation in the aphotic ocean. N2 fixation rates were low (average 0.63 ± 0.07 nmol N L−1 d−1) but consistently detected across all depths and stations, representing ∼ 6–88 % of photic N2 fixation. N2 fixation rates were not significantly correlated with DOM compounds. The analysis of nifH gene amplicons revealed a wide diversity of non-cyanobacterial diazotrophs, mostly matching clusters 1 and 3. Interestingly, a distinct phylotype from the major nifH subcluster 1G dominated at 650 dbar, coinciding with the oxygenated Subantarctic Mode Water (SAMW). This consistent pattern suggests that the distribution of aphotic diazotroph communities is to some extent controlled by water mass structure. While the data available are still too scarce to elucidate the distribution and controls of mesopelagic non-cyanobacterial diazotrophs in the WTSP, their prevalence in the mesopelagic layer and the consistent detection of active N2 fixation activity at all depths sampled during our study suggest that aphotic N2 fixation may contribute significantly to fixed nitrogen inputs in this area and/or areas downstream of water mass circulation.

Published
2018
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49. Pelagic N2fixation dominated by sediment diazotrophic communities in a shallow temperate estuary

Author

Hallstrøm, Søren, Benavides, Mar, Salamon, Ellen R., Evans, Clayton W., Potts, Lindsey J., Granger, Julie, Tobias, Craig R., Moisander, Pia H., and Riemann, Lasse

Abstract

Estuaries receive substantial anthropogenic nitrogen loading and are mainly considered net nitrogen sinks. While several studies have identified diverse diazotrophic communities in estuarine sediments, the role of pelagic diazotrophs in these systems is not well understood. We investigated the links between diazotrophic community composition, nitrogenase (nifH) gene expression, N2fixation, and environmental conditions in Narragansett Bay (USA). Pelagic N2fixation rates ranged between 0.02 and 9.41 nmol N L−1d−1and correlated significantly with fluctuations in diazotroph community composition. These fluctuations were also correlated with temperature, salinity, and mean sea level. The dominant sequences in our pelagic samples were related to sequences previously detected in the bay's sediments and were dominated by nifHgene Clusters I and III. We interpret this as a coupling between sediment and pelagic diazotroph communities and speculate that resuspension plays an important role for pelagic N2fixation in shallow estuarine environments such as Narragansett Bay. For instance, the finding of active sulfate reducers in the oxygenated water illustrates that the sediment‐pelagic coupling can impact nutrient cycling in shallow environments. The pelagic N2fixation measured during our study period showed only a minor contribution (< 1%) to the total estimated nitrogen load to Narragansett Bay. However, with intensifying nitrogen management in estuaries, the need to constrain the rates of pelagic N2fixation in these systems will be essential for estimating nitrogen fluxes within the bay and to the adjacent coastal ecosystems.

Published
2022
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50. High N 2 Fixation in and Near the Gulf Stream Consistent with a Circulation Control on Diazotrophy.

Author

Palter, Jaime B., Ames, Elana J., Benavides, Mar, Gonçalves Neto, Afonso, Granger, Julie, Moisander, Pia H., Watkins‐Brandt, Katie S., and White, Angelicque E.

Subjects
GULF Stream, NITROGEN fixation, FISHERIES, MARINE productivity, GREENHOUSE effect, OCEAN circulation
Abstract

The stoichiometry of physical nutrient supply may provide a constraint on the spatial distribution and rate of marine nitrogen (N2) fixation. Yet agreement between the N2 fixation rates inferred from nutrient supply and those directly measured has been lacking. The relative transport of phosphate and nitrate across the Gulf Stream suggests that 3–6 Tg N year−1 must be fixed to maintain steady nutrient stoichiometry in the North Atlantic subtropical gyre. Here we show direct measurements of N2 fixation consistent with these estimates, suggesting elevated N2 fixation in and near the Gulf Stream. At some locations across the Gulf Stream, we measured diazotroph abundances and N2 fixation rates that are 1–3 orders of magnitude greater than previously measured in the central North Atlantic subtropical gyre. In combination, rate measurements and gene abundances suggest that biogeochemical budgets can be a robust predictive tool for N2 fixation hot spots in the global ocean. Plain Language Summary: Marine photosynthetic organisms face a unique challenge: They are confined to the ocean's near‐surface layer where there is sufficient light for photosynthesis, yet the nutrients needed for growth are rapidly stripped from these layers. In response to this nutrient scarcity, some microorganisms, called diazotrophs, evolved the ability to tap into alternative resources: They convert the nitrogen gas that comprises a majority of the atmosphere and is abundantly dissolved in seawater into ammonium needed for growth. Diazotrophs regulate the rate of new nitrogen input to the ocean, which influences the productivity of marine fisheries, as well as how carbon dioxide is partitioned between the atmosphere (where it contributes to the greenhouse effect) and the ocean (where it does not). Therefore, understanding the controls on diazotrophy is a key oceanographic objective. It was previously hypothesized that the Gulf Stream region could be a hot spot of nitrogen fixation. In this work, we tested this hypothesis by measuring nitrogen fixation rates and diazotroph abundances across the Gulf Stream. We found robust diazotrophy, far exceeding that previously measured in the subtropical North Atlantic. Understanding the linkages between ocean circulation and N2 fixation helps us assess the vulnerability or stability of ocean biology and chemistry to future change. Key Points: The stoichiometry of nutrient supply predicts high N2 fixation rates in/near Gulf StreamMeasured N2 fixation rates in surface waters match expectations from a P* budget (order 10 nmol N L−1 day−1)Molecular analyses and microscopy confirm robust diazotrophy, with gradients possibly caused by convergent flow [ABSTRACT FROM AUTHOR]

Published
2020
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