EGU23-15628, updated on 26 Feb 2023
EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Simultaneous O2 and CO2 Flux Measurements with Custom-made Branch Chambers for Fagus sylvatica

Alexander Knohl1,2, Anne Klosterhalfen1, Jan Muhr1,3, Emanuel Blei1, Mattia Bonazza1, Dietmar Fellert1, Andrew Manning4, Christian Markwitz1, Penelope A. Pickers4, Frank Tiedemann1, Edgar Tunsch1, and Yuan Yan1
Alexander Knohl et al.
  • 1Bioclimatology, University of Göttingen, 37077 Göttingen, Germany
  • 2Centre of Biodiversity and Sustainable Land Use (CBL), University of Göttingen, 37073 Göttingen, Germany
  • 3Laboratory for Radioisotopes, Forest Botany and Tree Physiology, University of Göttingen, 37077 Göttingen, Germany
  • 4Centre for Ocean and Atmospheric Sciences, School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, United Kingdom

The O2:CO2 exchange ratio of plants is an only recently explored new plant trait and provides novel insights into the carbon cycle. Measurements of O2 fluxes at field sites are, however, scarce due to a number of technical challenges. This work presents unique field measurements of O2 and CO2 mole fractions and exchange fluxes of tree branches using a custom-made fully automated chamber system for quasi-continuous, high-precision measurements between Fagus sylvatica leaves and the atmosphere. Data from the vegetation period of 2021 in a temperate beech forest in Germany are shown.

Four steady-state, open-throughflow branch chambers were part of a larger chamber measurement set-up that also included four stem and eight soil chambers that were connected via a custom-built valve switching system to a modified FC-2 Differential Oxygen Analyzer (Oxzilla, Sable Systems International), and an LI-820 analyzer (LI-COR Biogeosciences GmbH). Precision was 1.3 ppm for O2 and 0.3 ppm for CO2. Both analyzers were located in an air-conditioned hut. O2 and CO2 mole fractions were measured continuously and logged in 10-sec intervals. Chambers were measured sequentially with typical observation times of 20-45 min per chamber, i.e. long enough for the mole fractions to reach steady state and allowing for at least two full measurement cycles of all sixteen chambers per day. For data processing, a quality check routine was developed for the branch chamber measurements, where spikes and non-steady-state conditions were excluded, and finally leaf exchange fluxes were quantified.

Diel, diurnal, and day-to-day variabilities were related to environmental and meteorological conditions. Further, the O2:CO2 exchange ratio on leaf-level was investigated for day- and nighttime. We could observe that the O2:CO2 exchange ratio varied stronger during nighttime than daytime and was affected mostly by the flux magnitude, the photosynthetically active radiation, and vapor pressure deficit. The exchange ratio was usually between 0.9 and 1.0 μmol μmol-1.

Finally, we evaluated simulated photosynthetical O2 and CO2 fluxes of an extended version of the one-dimensional, multi-layer atmosphere-biosphere gas exchange model CANVEG based on the obtained measurements.

How to cite: Knohl, A., Klosterhalfen, A., Muhr, J., Blei, E., Bonazza, M., Fellert, D., Manning, A., Markwitz, C., Pickers, P. A., Tiedemann, F., Tunsch, E., and Yan, Y.: Simultaneous O2 and CO2 Flux Measurements with Custom-made Branch Chambers for Fagus sylvatica, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15628,, 2023.