Hagi BucknWise at 23:28, 11 May 2026

2026-05-11T23:28:53Z

← Older revision		Revision as of 16:28, 11 May 2026
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	{{DISPLAYTITLE:Bulk uptake <sup>15</sup>N<sub>2</sub>}}		{{DISPLAYTITLE:Bulk uptake <sup>15</sup>N<sub>2</sub>}}
	{{BreadcrumbsNFixation}}		{{BreadcrumbsNFixation}}

			{{BreadcrumbsPrimaryProduction}}

			* [[Page authors\|Page authors]]: [[PRIMO]]
			* [[Responsible curator\|Responsible curator]]: [[User:Hagi BucknWise\|Hagen Buck-Wiese]]
			----

			__TOC__
			<div class="model-box">
			{\| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;"
			! N<sub>2</sub> fixation (bulk <sup>15</sup>N<sub>2</sub>)
			\|-
			\| '''Approach:''' <sup>15</sup>N<sub>2</sub> stable isotope tracer uptake
			\|-
			\| '''Context:''' incubation, ''in situ''
			\|-
			\| '''Spatial scale:''' point sample
			\|-
			\| '''Temporal scale:''' hours to one day
			\|-
			\| '''Units:''' nmol N L<sup>-1</sup> d<sup>-1</sup>; µmol N m<sup>-2</sup> d<sup>-1</sup> (depth-integrated)
			\|-
			\| '''Community captured:''' bulk, size-fractionated
			\|-
			\| '''Co-measurements:''' background δ<sup>15</sup>N (PON), <sup>15</sup>N<sub>2</sub> enrichment of dissolved phase; can couple with <sup>13</sup>CO<sub>2</sub> uptake
			\|}
			</div>
			<div style="clear:both"></div>

			== Method Overview ==

			<sup>15</sup>N<sub>2</sub> gas is dissolved into seawater and added to incubation bottles, labelling the dissolved N<sub>2</sub> pool. Diazotrophic microorganisms fix the labelled N<sub>2</sub>, incorporating <sup>15</sup>N into their biomass. After incubation, the particulate fraction is collected on pre-combusted GF/F filters; the <sup>15</sup>N enrichment in particulate nitrogen (PN) is measured by EA-IRMS. The N<sub>2</sub> fixation rate is calculated from the <sup>15</sup>N excess in PN relative to the <sup>15</sup>N enrichment of the dissolved N<sub>2</sub> pool, measured by MIMS or GC-IRMS<ref name="Montoya1996">Montoya, J. P., Voss, M., Kähler, P., & Capone, D. G. (1996). A simple, high-precision, high-sensitivity tracer assay for N<sub>2</sub> fixation. ''Applied and Environmental Microbiology'', 62(3), 986–993. https://doi.org/10.1128/aem.62.3.986-993.1996</ref>.

			Two labelling approaches are used: (1) direct injection of <sup>15</sup>N<sub>2</sub> gas bubbles followed by vigorous shaking and equilibration; and (2) the dissolution method, in which pre-dissolved <sup>15</sup>N<sub>2</sub>-enriched water is injected, achieving more homogeneous labelling. The method can be coupled with <sup>13</sup>CO<sub>2</sub> uptake in the same incubation to simultaneously measure N<sub>2</sub> fixation and carbon fixation by diazotrophs.

			=== Scale of measurement ===

			Each incubation provides a point measurement. Depth-integrated fixation rates are obtained by incubating bottles collected from multiple depths and integrating over the euphotic zone. Incubation duration is typically hours to one day.

			=== Data generated ===

			N<sub>2</sub> fixation rates in nmol N L<sup>-1</sup> d<sup>-1</sup> or µmol N m<sup>-2</sup> d<sup>-1</sup> (depth-integrated). Rates can be size-fractionated (e.g., 0.2–10 µm versus > 10 µm) to attribute fixation to different diazotroph size classes (unicellular vs. filamentous). Fixed nitrogen can also be tracked into the dissolved organic nitrogen (DON) pool.

			=== Units & currency ===

			Units are nmol N L<sup>-1</sup> d<sup>-1</sup> or µmol N m<sup>-2</sup> d<sup>-1</sup>. The currency is nitrogen.

			=== Sample size ===

			Typical samples are 1–5 L in volume per incubation.

			=== Repositories & databases ===

			== Limitations ==

			The <sup>15</sup>N<sub>2</sub> enrichment of the dissolved pool must be measured accurately; under-estimation of the <sup>15</sup>N<sub>2</sub> enrichment (e.g., due to incomplete equilibration of bubbles) leads to overestimation of fixation rates. Bubble injection produces heterogeneous enrichment across replicate bottles; the dissolution method mitigates this. Diazotroph community composition affects the timing of fixation: Crocosphaera fixes N<sub>2</sub> primarily at night, UCYN-A primarily during the day. Bottle effects apply.

			== Example Applications & Protocols ==

			=== Classic examples ===
			* Montoya et al. (1996) ''A simple, high-precision, high-sensitivity tracer assay for N<sub>2</sub> fixation'' <ref name="Montoya1996" />
			* Wilson et al. (2012) ''Comparative assessment of nitrogen fixation methodologies, conducted in the oligotrophic North Pacific Ocean'' <ref name="Wilson2012">Wilson, S. T., Böttjer, D., Church, M. J., & Karl, D. M. (2012). Comparative assessment of nitrogen fixation methodologies, conducted in the oligotrophic North Pacific Ocean. ''Applied and Environmental Microbiology'', 78(18), 6516–6523. https://doi.org/10.1128/AEM.01146-12</ref>
			* Großkopf et al. (2012) ''Doubling of marine dinitrogen-fixation rates based on direct measurements'' <ref name="Großkopf2012">Großkopf, T., Mohr, W., Baustian, T., Schunck, H., Gill, D., Kuypers, M. M. M., Lavik, G., Schmitz, R. A., Wallace, D. W. R., & LaRoche, J. (2012). Doubling of marine dinitrogen-fixation rates based on direct measurements. ''Nature'', 488(7411), 361–364. https://doi.org/10.1038/nature11338</ref>

			=== Recent applications ===
			* Tschitschko et al. (2024) ''Rhizobia–diatom symbiosis fixes missing nitrogen in the ocean'' <ref name="Tschitschko2024">Tschitschko, B., Landa, M., Cheung, S., Zheng, H., Williams, C. M., Vergin, K., Giovannoni, S. J., Rocap, G., & Lindell, D. (2024). Rhizobia–diatom symbiosis fixes missing nitrogen in the ocean. ''Nature'', 630, 899–904. https://doi.org/10.1038/s41586-024-07495-w</ref>

			=== Common calculations/conversions ===
			* N<sub>2</sub> fixation rate (nmol N L<sup>-1</sup> d<sup>-1</sup>) = [(<sup>15</sup>N<sub>PN,final</sub> − <sup>15</sup>N<sub>PN,initial</sub>) / (<sup>15</sup>N<sub>N2,dissolved</sub> − <sup>15</sup>N<sub>natural</sub>)] × [PN] / incubation time.
			* Depth-integrated rate (µmol N m<sup>-2</sup> d<sup>-1</sup>) = ∫ rate(z) dz over the euphotic zone.

			== References ==

			[[Category:Main Pages\|Model types]]

Kate Evans at 19:34, 11 February 2026

2026-02-11T19:34:02Z

← Older revision		Revision as of 12:34, 11 February 2026
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			{{BreadcrumbsNFixation}}

Kate Evans at 20:56, 2 February 2026

2026-02-02T20:56:56Z

← Older revision		Revision as of 13:56, 2 February 2026
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	~~testing~~		{{DISPLAYTITLE:Bulk uptake <sup>15</sup>N<sub>2</sub>}}

Kate Evans: Created page with "testing"

2026-02-02T20:55:18Z

Created page with "testing"

New page

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Bulk uptake 15N2 - Revision history

Hagi BucknWise at 23:28, 11 May 2026

Kate Evans at 19:34, 11 February 2026

Kate Evans at 20:56, 2 February 2026

Kate Evans: Created page with "testing"