, Volume 168, Issue 2, pp 335–342 | Cite as

N2 fixation estimates in real-time by cavity ring-down laser absorption spectroscopy

  • Nicolas Cassar
  • Jean-Philippe Bellenger
  • Robert B. Jackson
  • Jonathan Karr
  • Bruce A. Barnett
Physiological ecology - Original Paper


The most common currency for estimating N2 fixation is acetylene reduction to ethylene. Real-time estimates of nitrogen fixation are needed to close the global nitrogen budget and these remain a critical gap in both laboratory and field experiments. We present a new method for continuous real-time measurements of ethylene production: Acetylene Reduction Assays by Cavity ring-down laser Absorption Spectroscopy (ARACAS). In ARACAS, air in the headspace of an incubation chamber is circulated with a diaphragm pump through a cavity ring-down ethylene spectrometer and back to the incubation chamber. This paper describes the new approach and its benefits compared to the conventional detection of ethylene by flame ionization detector gas chromatography. First, the detection of acetylene reduction to ethylene is non-intrusive and chemically non-destructive, allowing for real-time measurements of nitrogenase activity. Second, the measurements are made instantaneously and continuously at ppb levels, allowing for observation of real-time kinetics on time intervals as short as a few seconds. Third, the instrument can be automated for long time periods of measurement. Finally, the technique will be widely accessible by the research community as it can be readily adapted to most existing acetylene reduction protocols and is based on a modestly priced, commercially available instrument. We illustrate its use for measuring N2 fixation using two species, the diazotrophic bacterium Azotobacter vinelandii and the lichen Peltigera praetextata. We also discuss potential limitations of the approach, primarily the implications of leaks in the analyzer, as well as future improvements.


Acetylene reduction Cavity ring-down spectroscopy N2 fixation Method development ARACAS 



We would like to thank François Lutzoni (Duke) and Brendan Hodkinson (Duke) for collection and identification of the lichen sample, and Aaron Van Pelt (Picarro) for helpful discussions. This work was supported by the National Science Foundation (DEB Ecosystems #1050227) (N.C. and R.B.J.) and the Canadian Research Chair in Terrestrial Biogeochemistry (J.P.B.). We acknowledge additional support from the Office of the Provost, Department of Biology, and Center on Global Change at Duke University.

Supplementary material

442_2011_2105_MOESM1_ESM.doc (150 kb)
Supplementary material 1 (DOC 150 kb)


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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Nicolas Cassar
    • 1
  • Jean-Philippe Bellenger
    • 2
  • Robert B. Jackson
    • 1
    • 3
  • Jonathan Karr
    • 1
  • Bruce A. Barnett
    • 1
  1. 1.Division of Earth and Ocean Sciences, Nicholas School of the EnvironmentDuke UniversityDurhamUSA
  2. 2.Département de ChimieUniversité de SherbrookeSherbrookeCanada
  3. 3.Center on Global Change and Biology DepartmentDuke UniversityDurhamUSA

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