Preprints
https://doi.org/10.5194/bg-2022-32
https://doi.org/10.5194/bg-2022-32
 
04 Feb 2022
04 Feb 2022
Status: this preprint was under review for the journal BG. A revision for further review has not been submitted.

Intercomparison of methods to estimate GPP based on CO2 and COS flux measurements

Kukka-Maaria Kohonen1, Roderick Dewar1,2, Gianluca Tramontana3,4, Aleksanteri Mauranen1, Pasi Kolari1, Linda M. J. Kooijmans5, Dario Papale6,7, Timo Vesala1,8,9, and Ivan Mammarella1 Kukka-Maaria Kohonen et al.
  • 1Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, Finland
  • 2Plant Sciences Division, Research School of Biology, The Australian National University, Canberra, ACT 2601, Australia
  • 3Image Processing Laboratory (IPL), Parc Científic Universitat de València, Universitat de València, Paterna, Spain
  • 4Terrasystem s.r.l, Viterbo, Italy
  • 5Meteorology and Air Quality, Wageningen University and Research, Wageningen, The Netherlands
  • 6DIBAF, Department for Innovation in Biological, Agro-food and Forestry Systems, University of Tuscia, Viterbo, Italy
  • 7IAFES, Euro-Mediterranean Center on Climate Change (CMCC), Viterbo, Italy
  • 8Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Helsinki, Finland
  • 9Yugra State University, 628012, Khanty-Mansiysk, Russia

Abstract. Knowing the components of ecosystem scale carbon exchange is crucial in order to develop better models and future predictions of the terrestrial carbon cycle. However, there are several uncertainties and unknowns related to current photosynthesis estimates. In this study, we test the use of four different methods for quantifying photosynthesis at the ecosystem scale, of which two are based on carbon dioxide (CO2) and two on carbonyl sulfide (COS) flux measurements. The CO2-based methods use traditional flux partitioning and artificial neural networks to separate the net CO2 flux into respiration and photosynthesis. The COS-based methods make use of a unique five year COS flux data set at a boreal forest and include two different approaches to determine the leaf scale uptake ratio of COS and CO2 (LRU), of which one (LRUCAP) was developed in this study. LRUCAP was based on stomatal conductance theories, while the other was based on an empirical relation to measured radiation (LRUPAR).

We found that for the measurement period 2013–2017 the artificial neural networks method gave a GPP estimate very close to that of traditional flux partitioning at all time scales. COS-based methods gave on average higher GPP estimates than the CO2-based estimates on daily (23 and 7 % higher, if using LRUPAR or LRUCAP in GPP calculation, respectively) and monthly scales (20 and 3 % higher), as well as a higher cumulative sum over three months in all years (on average 25 and 3 % higher). LRUCAP was higher than measured LRU at high radiation leading to an underestimated GPP during midday. However, in general it compared better with the CO2-based methods than LRUPAR -based GPP calculations. The applicability of LRUCAP at other measurement sites is potentially better than that of LRUPAR since its parameters are based on literature values and simple meteorological measurements, while the radiation relation in LRUPAR might be site-specific. This, however, requires further testing at other measurement sites.

Kukka-Maaria Kohonen et al.

Status: closed (peer review stopped)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-32', Anonymous Referee #1, 01 Mar 2022
    • AC1: 'Reply on RC1', Kukka-Maaria Kohonen, 15 Apr 2022
  • RC2: 'Comment on Kohonen et al. (2022). Biogeosciences Discussions, bg-2022-32.', Anonymous Referee #2, 12 Mar 2022
    • AC2: 'Reply on RC2', Kukka-Maaria Kohonen, 15 Apr 2022

Status: closed (peer review stopped)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-32', Anonymous Referee #1, 01 Mar 2022
    • AC1: 'Reply on RC1', Kukka-Maaria Kohonen, 15 Apr 2022
  • RC2: 'Comment on Kohonen et al. (2022). Biogeosciences Discussions, bg-2022-32.', Anonymous Referee #2, 12 Mar 2022
    • AC2: 'Reply on RC2', Kukka-Maaria Kohonen, 15 Apr 2022

Kukka-Maaria Kohonen et al.

Kukka-Maaria Kohonen et al.

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Short summary
Four different methods for quantifying photosynthesis (GPP) at ecosystem scale were tested, of which two are based on carbon dioxide (CO2) and two on carbonyl sulfide (COS) flux measurements. CO2-based methods are traditional partitioning and a new method using machine learning. We introduce a novel method for calculating GPP from COS fluxes, with potentially better applicability than the former methods. Both COS-based methods gave on average higher GPP estimates than the CO2-based estimates.
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