02 Mar 2023
 | 02 Mar 2023
Status: this preprint is currently under review for the journal BG.

A Modeling Approach to Investigate Drivers, Variability and Uncertainties in O2 Fluxes and the O2 : CO2 Exchange Ratios in a Temperate Forest

Yuan Yan, Anne Klosterhalfen, Fernando Moyano, Matthias Cuntz, Andrew C. Manning, and Alexander Knohl

Abstract. The O2 : CO2 exchange ratio (ER) between terrestrial ecosystems and the atmosphere is a key parameter for partitioning global ocean and land carbon fluxes. The long-term terrestrial ER is considered to be close to 1.10 moles of O2 consumed per mole of CO2 produced. Due to the technical challenge in measuring directly the ER of entire terrestrial ecosystems (EReco), little is known about the variations in ER at the hourly and seasonal scales as well as how different components contribute to EReco. In this modeling study, we explore the variability and drivers of EReco and evaluate the hypothetical uncertainty in determining ecosystem O2 fluxes based on current instrument precision. We adapted the one-dimensional, multi-layer atmosphere-biosphere gas exchange model, CANVEG, to simulate hourly EReco from modeled O2 and CO2 fluxes in a temperate beech forest in Germany.

We found that the annual mean EReco ranged from 1.06 to 1.12 mol mol-1 within the five years’ study period. Hourly EReco showed strong variations over diel and seasonal cycles and within the vertical canopy profile. Determination of ER from O2 and CO2 mole fractions in air above and within the canopy (ERconc) varied between 1.115 and 1.15 mol mol-1. CANVEG simulations also indicated that ecosystem O2 fluxes could be derived using the flux-gradient method in combination with measurements of vertical scalar gradients and CO2, sensible heat or latent heat fluxes obtained with the eddy covariance technique. Owing to measurement uncertainties, however, the uncertainty in estimated O2 fluxes derived with the flux-gradient approach could be as high as 15 μmol m-2 s-1, which represented the 90 % quantile of the uncertainty in hourly data with a high-accuracy instrument. We also demonstrated that O2 fluxes can be used to partition net CO2 exchange fluxes into their component fluxes of photosynthesis and respiration, if EReco is known. The uncertainty of the partitioned gross assimilation ranged from 1.43 to 4.88 μmol m-2 s-1 assuming a measurement uncertainty of 0.1 or 2.5 μmol m-2 s-1 for net ecosystem CO2 exchange and from 0.1 to 15 μmol m-2 s-1 for net ecosystem O2 exchange, respectively. Our analysis suggests that O2 measurements at ecosystem scale have the potential for partitioning net CO2 fluxes into their component fluxes, but further improvement in instrument precision is needed.

Yuan Yan et al.

Status: open (until 13 Apr 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2023-30', Anonymous Referee #1, 07 Mar 2023 reply
    • AC1: 'Reply on RC1', Yuan Yan, 22 Mar 2023 reply
  • CC1: 'Comment on bg-2023-30', Andrew Kowalski, 13 Mar 2023 reply

Yuan Yan et al.

Yuan Yan et al.


Total article views: 186 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
144 32 10 186 3 5
  • HTML: 144
  • PDF: 32
  • XML: 10
  • Total: 186
  • BibTeX: 3
  • EndNote: 5
Views and downloads (calculated since 02 Mar 2023)
Cumulative views and downloads (calculated since 02 Mar 2023)

Viewed (geographical distribution)

Total article views: 210 (including HTML, PDF, and XML) Thereof 210 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 24 Mar 2023
Short summary
A higher understanding of O2 fluxes, their exchange ratios with CO2 and their interrelations with environmental conditions would provide further insights in biogeochemical ecosystem processes. We, therefore, used the multi-layer canopy model, CANVEG, to simulate and analyze the flux exchange for our forest study site for 2012–2016. Based on these simulations, we further tested successfully the application of various micrometeorological methods and the prospects of real O2 flux measurements.