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{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;" ! Denitrification enzyme activity (acetylene block) |- | '''Approach:''' acetylene inhibition of N₂O reductase; GC measurement of N₂O accumulation |- | '''Context:''' incubation, l..."

2026-05-12T22:56:51Z

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;" ! Denitrification enzyme activity (acetylene block) |- | '''Approach:''' acetylene inhibition of N2O reductase; GC measurement of N2O accumulation |- | '''Context:''' incubation, l..."

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{{BreadcrumbsNutrients}}

* [[Page authors|Page authors]]: [[PRIMO]]
* [[Responsible curator|Responsible curator]]: [[User:Hagi BucknWise|Hagen Buck-Wiese]]
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<div class="model-box">
{| class="model-ib" style="float:right; margin-left:1em; margin-bottom:1em;"
! Denitrification enzyme activity (acetylene block)
|-
| '''Approach:''' acetylene inhibition of N2O reductase; GC measurement of N2O accumulation
|-
| '''Context:''' incubation, lab
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| '''Spatial scale:''' point sample
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| '''Temporal scale:''' minutes to hours
|-
| '''Units:''' nmol N2O-N L-1 h-1
|-
| '''Community captured:''' bulk
|-
| '''Co-measurements:''' nitrate, oxygen, acetylene
|}
</div>
<div style="clear:both"></div>

== Method Overview ==

Acetylene (C2H2) at ~10 kPa partial pressure blocks the final step of denitrification, the reduction of N2O to N2 by N2O reductase (nosZ). In acetylene-amended, anoxic incubations supplied with saturating nitrate, denitrifiers reduce NO3- → NO2- → NO → N2O, but cannot proceed further to N2. The accumulating N2O is measured by gas chromatography (GC-FID or GC-ECD) and the rate of N2O accumulation provides an estimate of denitrification enzyme activity (DEA)<ref name="Balderston1976">Balderston, W. L., Sherr, B., & Payne, W. J. (1976). Blockage by acetylene of nitrous oxide reduction in Pseudomonas perfectomarinus. ''Applied and Environmental Microbiology'', 31(4), 504–508. https://doi.org/10.1128/aem.31.4.504-508.1976</ref>. Because nitrate is provided at saturating concentrations, the assay measures potential (Vmax) rather than ''in situ'' denitrification activity.

=== Scale of measurement ===

Point sample; short incubations (minutes to hours) under anoxic conditions with nitrate and acetylene amendments.

=== Data generated ===

N2O-N accumulation rates (nmol N2O-N L-1 h-1), which provide a proxy for potential denitrification enzyme activity. These rates overestimate ''in situ'' denitrification because they are measured at saturating nitrate and anoxia.

=== Units & currency ===

Units are nmol N2O-N L-1 h-1. The currency is N2O (nitrogen equivalent).

=== Sample size ===

Samples are typically 250 mL to 1 L in volume.

=== Repositories & databases ===

== Limitations ==

Acetylene assumes complete blockage of N2O reductase, but incomplete inhibition can occur, particularly at low acetylene concentrations. Acetylene also inhibits nitrification (AMO) and can scavenge nitric oxide (NO), creating additional artifacts. The theoretical assumptions of complete anoxia and saturating nitrate may not reflect ''in situ'' conditions. The method measures potential activity, not actual ''in situ'' denitrification rates.

== Example Applications & Protocols ==

=== Classic examples ===
* Balderston et al. (1976) ''Blockage by acetylene of nitrous oxide reduction in Pseudomonas perfectomarinus'' <ref name="Balderston1976" />

=== Recent applications ===
* Groffman et al. (2006) ''Methods for measuring denitrification: diverse approaches to a difficult problem'' <ref name="Groffman2006">Groffman, P. M., Altabet, M. A., Böhlke, J. K., Butterbach-Bahl, K., David, M. B., Firestone, M. K., Giblin, A. E., Kana, T. M., Nielsen, L. P., & Voytek, M. A. (2006). Methods for measuring denitrification: diverse approaches to a difficult problem. ''Ecological Applications'', 16(6), 2091–2122. https://doi.org/10.1890/1051-0761(2006)016[2091:MFMDDA]2.0.CO;2</ref>

=== Common calculations/conversions ===
* DEA (nmol N L-1 h-1) = Δ[N2O] / time; assuming equimolar conversion from NO3- via N2O.

== References ==

[[Category:Main Pages|Model types]]

Acetylene-block proxy for denitrifcation enzyme activity - Revision history