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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Nitrifier dark CO₂ fixation (inhibitor + tracer) |- | '''Approach:''' dark ¹⁴C or ¹³C uptake with nitrification inhibitors |- | '''Context:''' incubation, lab |- | '''..."

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Created page with "{{BreadcrumbsNutrients}} * Page authors: PRIMO * Responsible curator: Hagen Buck-Wiese ---- __TOC__ <div class="model-box"> {| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Nitrifier dark CO2 fixation (inhibitor + tracer) |- | '''Approach:''' dark 14C or 13C uptake with nitrification inhibitors |- | '''Context:''' incubation, lab |- | '''..."

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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;"
! Nitrifier dark CO2 fixation (inhibitor + tracer)
|-
| '''Approach:''' dark 14C or 13C uptake with nitrification inhibitors
|-
| '''Context:''' incubation, lab
|-
| '''Spatial scale:''' point sample
|-
| '''Temporal scale:''' hours to days
|-
| '''Units:''' nmol C L-1 d-1; mol C cell-1 d-1
|-
| '''Community captured:''' bulk, size-fractionated, single cell
|-
| '''Co-measurements:''' cell numbers, community composition
|}
</div>
<div style="clear:both"></div>

== Method Overview ==

The chemoautotrophic CO2 fixation attributable specifically to nitrifiers is estimated by comparing dark 14C or 13C-bicarbonate incorporation in paired incubations: one with nitrification inhibitors (ATU, octyne) and one without. The difference in dark carbon fixation between control and inhibited bottles is attributed to nitrifier chemoautotrophic production. This approach is based on the principle that nitrifying bacteria and archaea derive energy from NH4+ or NO2- oxidation and fix CO2 as their sole carbon source<ref name="Ward2011">Ward, B. B. (2011). Measurement and distribution of nitrification rates in the oceans. ''Methods in Enzymology'', 486, 307–323. https://doi.org/10.1016/B978-0-12-381294-0.00013-4</ref>.

=== Scale of measurement ===

Point sample; dark incubations of hours to days. Requires strict exclusion of light to prevent phytoplankton photosynthetic CO2 fixation from contaminating the signal.

=== Data generated ===

Nitrifier-specific dark carbon fixation rates in nmol C L-1 d-1; convertible to nitrification rates using the theoretical yield of 1 mol CO2 fixed per ~7 mol NH4+ oxidized (AOA; ratio differs for AOB).

=== Units & currency ===

Units are mol C L-1 d-1 or mol C cell-1 d-1. The currency is carbon.

=== Sample size ===

Typical samples are ~1 L in volume.

=== Repositories & databases ===

== Limitations ==

The method assumes that nitrification is the primary driver of dark CO2 fixation in the water column. Recent evidence suggests this assumption is increasingly questionable in some environments where other chemoautotrophs (sulphur oxidisers, hydrogen oxidisers) contribute substantially. Long incubations in the dark can alter community composition. The conversion factor between CO2 fixation and N oxidation varies among nitrifier lineages and must be determined empirically.

== Example Applications & Protocols ==

=== Classic examples ===
* Ward (2011) ''Measurement and distribution of nitrification rates in the oceans'' <ref name="Ward2011" />

=== Recent applications ===
*

=== Common calculations/conversions ===
* Nitrification rate from dark C fixation: assuming 1 mol CO2 fixed per 7 mol NH4+ oxidised, nitrification rate (nmol N L-1 d-1) = dark C fixation (nmol C L-1 d-1) × 7.

== References ==

[[Category:Main Pages|Model types]]

Inhibitors with 14 or 13CO2 uptake - Revision history