Sensitivity of Trichodesmium erythraeum and Crocosphaera watsonii abundance and N&lt;sub&gt;2 fixation rates to varying NO&lt;sub&gt;3&lt;sup&gt;− and PO&lt;sub&gt;4&lt;sup&gt;3− concentrations in batch cultures

Knapp, Angela N.; Dekaezemacker, Julien; Bonnet, Sophie; Sohm, Jill A.; Capone, Douglas G.

doi:10.3354/ame01577

Cited by 59 publications

(71 citation statements)

References 82 publications

(121 reference statements)

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“…In particular, N 2 fixation has been described as a very "patchy" process in the ocean (Bombar et al, 2015). Many factors control the distribution and activity of diazotrophs such as temperature Moisander et al, 2010;Raveh et al, 2015;Staal et al, 2003), nutrient availability (mainly phosphate and iron) (e.g., Mills et al, 2004), pCO 2 (e.g., Levitan et al, 2007), ambient concentrations of fixed N (NO − 3 and NH + 4 ) (e.g., Knapp et al, 2012), and physical forcing (e.g., Fong et al, 2008). Most studies dedicated to understanding the controls on marine N 2 fixation have been undertaken along large oceanic transects; these are particularly valuable and have recently led to the compilation of a global ocean database of diazotrophy (Luo et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Dynamics of N<sub>2</sub> fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)

et al. 2016

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Abstract. N 2 fixation rates were measured daily in large (∼ 50 m 3 ) mesocosms deployed in the tropical southwest Pacific coastal ocean (New Caledonia) to investigate the temporal variability in N 2 fixation rates in relation with environmental parameters and study the fate of diazotrophderived nitrogen (DDN) in a low-nutrient, low-chlorophyll ecosystem. The mesocosms were fertilized with ∼ 0.8 µM dissolved inorganic phosphorus (DIP) to stimulate diazotrophy. Bulk N 2 fixation rates were replicable between the three mesocosms, averaged 18.5 ± 1.1 nmol N L −1 d −1 over the 23 days, and increased by a factor of 2 during the second half of the experiment (days 15 to 23) to reach 27.3 ± 1.0 nmol N L −1 d −1 . These later rates measured after the DIP fertilization are higher than the upper range reported for the global ocean. During the 23 days of the experiment, N 2 fixation rates were positively correlated with seawater temperature, primary production, bacterial production, standing stocks of particulate organic carbon (POC), nitrogen (PON) and phosphorus (POP), and alkaline phosphatase activity, and negatively correlated with DIP concentrations, DIP turnover time, nitrate, and dissolved organic nitrogen and phosphorus concentrations. The fate of DDN was investigated during a bloom of the unicellular diazotroph UCYN-C that occurred during the second half of the experiment. Quantification of diazotrophs in the sediment traps indicates that ∼ 10 % of UCYN-C from the water column was exported daily to the traps, representing as much as 22.4 ± 5.5 % of the total POC exported at the height of the UCYN-C bloom. This export was mainly due to the aggregation of small (5.7 ± 0.8 µm) UCYN-C cells into large (100-500 µm) aggregates. During the same time period, a DDN transfer experiment based on high-resolution nanometerscale secondary ion mass spectrometry (nanoSIMS) coupled with 15 N 2 isotopic labeling revealed that 16 ± 6 % of the DDN was released to the dissolved pool and 21 ± 4 % was transferred to non-diazotrophic plankton, mainly picoplankton (18 ± 4 %) followed by diatoms (3 ± 2 %). This is consistent with the observed dramatic increase in picoplankton and diatom abundances, primary production, bacterial production, and standing stocks of POC, PON, and POP in the

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Section: Introductionmentioning

confidence: 99%

Dynamics of N<sub>2</sub> fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)

et al. 2016

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“…Recent laboratory experiments have qualified nitrogen inhibition by showing that DNF can occur when diazotrophs are acclimated to chronic high DIN concentrations, although at a lower rate than at low DIN concentration (Knapp, 2012;Knapp et al, 2012). DIN inhibition may be offset by phosphorus supply in iron-replete conditions as observed in laboratory experiments and field studies (Fernandez et al, 2011(Fernandez et al, , 2015.…”

Section: Is the Distribution Of Dnf Gaussian?mentioning

confidence: 97%

“…DIN inhibition may be offset by phosphorus supply in iron-replete conditions as observed in laboratory experiments and field studies (Fernandez et al, 2011(Fernandez et al, , 2015. Knapp et al (2012) suggest that enhanced abundance of diazotrophs in P-and Fe-rich waters offsets reduced DNF due to nitrogen inhibition, resulting in DNF rates similar to low DIN conditions. In CESM, however, iron deficiency limits DNF in the southeastern tropical Pacific so that spatial coupling between DNF and denitrification is weak (Moore et al, 2007).…”

Section: Is the Distribution Of Dnf Gaussian?mentioning

confidence: 99%

“…The diversity of parameterizations in the CMIP5 models makes this data set potentially useful for understanding these processes as new observations emerge, although model error in processes such as ventilation and denitrification may limit their usefulness in some cases. Recent laboratory experiments have qualified nitrogen inhibition by showing that DNF can occur when diazotrophs are acclimated to chronic high DIN concentrations, although at a lower rate than at low DIN concentration (Knapp, 2012;Knapp et al, 2012). DIN inhibition may be offset by phosphorus supply in iron-replete conditions as observed in laboratory experiments and field studies (Fernandez et al, 2011(Fernandez et al, , 2015.…”

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Ocean dinitrogen fixation and its potential effects on ocean primary production in Earth system model simulations of anthropogenic warming

Riche

Christian

2018

Elementa: Science of the Anthropocene

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Dinitrogen fixation (DNF) provides a large fraction of the 'new' nitrogen supporting upper ocean productivity, and is associated with environmental conditions likely to show substantial change under anthropogenic warming. For example, surface warming induces stronger stratification, weaker nutrient supply and more rapid nutrient depletion. Using six Earth System Models, we have examined spatial patterns and trends of DNF in the CMIP5 historical and RCP 8.5 experiments. Four models (CanESM2, CESM1-BGC, IPSL-CM5R-LR, and UVicESCM) show high DNF rates in warm, stratified waters mostly associated with the western parts of the ocean basins, while GFDL-ESM2M and MPI-ESM-LR show elevated rates near the eastern boundaries because of coupling of DNF and denitrification. Despite a growing body of data, the spatial pattern of DNF is still insufficiently resolved by available observations, and none of the models agrees well with the observations. Modelled and observed rates are mostly in the same general range except for UVicESCM, and frequency distributions are similar, but spatial pattern correlations are weak and in most cases not statistically significant. Only a few models show strong trends in DNF and primary production in a warming climate, and the signs of the trends are inconsistent. Observations of primary production at the benchmark subtropical station ALOHA (22.75°N, 158°W) and proxies for historical DNF from the same region appear to corroborate trends in CanESM2 that are not present in other models. However, the CanESM DNF parameterization does not include any limitation by P or Fe, so modelled future trends may not materialize due to nutrient limitation. Analysis of available models and observations suggests that our understanding of environmental controls on ocean DNF remains limited and future trends are highly uncertain. Long-term global simulations of DNF will only be meaningful if we maintain long-term observations and extend coverage to undersampled regions.Keywords: ocean dinitrogen fixation; Earth system modelling; anthropogenic climate change Riche and Christian: Ocean dinitrogen fixation and its potential effects on ocean primary production in Earth system model simulations of anthropogenic warming Art. 16, page 2 of 18 of phosphorus or iron are available, with opposing effects on primary production (Karl et al., 1995(Karl et al., , 1997Karl, 1999). As diazotrophic phytoplankton thrive in warm, stratified waters (Sohm et al., 2011), investigating the potentially enhanced role of diazotrophs in tropical and subtropical ocean ecosystems in a warming climate is important. Proxy δ 15N measurements of the DNF contribution to the N inventory in the subtropical Pacific suggest that the recent apparent enhancement discussed by Karl (1999) is a long-term trend throughout the 20 th century, possibly associated with anthropogenic warming (Sherwood et al., 2014).We have examined trends in DNF in a variety of Earth System Models associated with the CMIP5 project (Taylor et al., 2012) to determine which if any sh...

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“…However, there is growing evidence that N 2 fixation occurs under N-rich conditions (Fernandez et al, 2011;Knapp, 2012;Knapp et al, 2012;Dekaezemacker et al, 2013;Meyer et al, 2016) and even within upwelling regions of the Benguela and equatorial Atlantic (Sohm et al, 2011;Subramaniam et al, 2013). An explanation based on the genetic regulation of certain diazotrophs has just been provided by Bombar et al (2016).…”

Section: Non-redfield Nutrient Assimilationmentioning

confidence: 99%

Mechanisms of P* Reduction in the Eastern Tropical South Pacific

et al. 2017

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Water masses influenced by oxygen minimum zones (OMZ) feature low inorganic nitrogen (N) to phosphorus (P) ratios. The surplus of P over N is thought to favor non-Redfield primary production by bloom-forming phytoplankton species. Additionally, excess phosphate (P * ) is thought to provide a niche for nitrogen fixing organisms. In order to assess the effect of low inorganic nutrient ratios on the stoichiometry and composition of primary producers, biogeochemical measurements were carried out in 2012 during a research cruise in the eastern tropical South Pacific (ETSP). Based on pigment analyses, a succession of different phytoplankton functional groups was observed along onshore-offshore transects with diatoms dominating the productive upwelling region, and prymnesiophytes, cryptophytes, and Synechococcus prevailing in the oligotrophic open ocean. Although inorganic nutrient supply ratios were below Redfield proportions throughout the sampling area, the stoichiometry of particulate organic nitrogen to phosphorus (PON:POP) generally exceeded ratios of 16:1. Despite PON:POP ≥ 16, high P * -values in the surface layer (0-50 m) above the shelf rapidly decreased as water masses were advected offshore. There are three mechanisms which can explain these observations: (1) non-Redfield primary production, where the excess phosphorus in the biomass is directly released as dissolved organic phosphorus (DOP), (2) non-Redfield primary production, which is masked by a particulate organic matter pool mainly consisting of P-depleted detrital biomass, and/or (3) Redfield primary production combined with dinitrogen (N 2 ) fixation. Our observations suggest that the three processes occur simultaneously in the study area; quantifying the relative importance of each of these mechanisms needs further investigation. Therefore, it remains uncertain whether the ETSP is a net sink for bioavailable N or whether the N-deficit in this area is replenished locally.

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Sensitivity of Trichodesmium erythraeum and Crocosphaera watsonii abundance and N<sub>2 fixation rates to varying NO<sub>3<sup>− and PO<sub>4<sup>3− concentrations in batch cultures

Cited by 59 publications

References 82 publications

Dynamics of N<sub>2</sub> fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)

Dynamics of N<sub>2</sub> fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)

Ocean dinitrogen fixation and its potential effects on ocean primary production in Earth system model simulations of anthropogenic warming

Mechanisms of P* Reduction in the Eastern Tropical South Pacific

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Sensitivity of Trichodesmium erythraeum and Crocosphaera watsonii abundance and N<sub>2 fixation rates to varying NO<sub>3<sup>− and PO<sub>4<sup>3− concentrations in batch cultures

Cited by 59 publications

References 82 publications

Dynamics of N&lt;sub&gt;2&lt;/sub&gt; fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)

Dynamics of N&lt;sub&gt;2&lt;/sub&gt; fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)

Ocean dinitrogen fixation and its potential effects on ocean primary production in Earth system model simulations of anthropogenic warming

Mechanisms of P* Reduction in the Eastern Tropical South Pacific

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Dynamics of N<sub>2</sub> fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)

Dynamics of N<sub>2</sub> fixation and fate of diazotroph-derived nitrogen in a low-nutrient, low-chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)