EGU2020-11242, updated on 22 Jan 2021
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Towards a better understanding of soil- and tree stem-atmosphere exchanges of greenhouse gases, i.e. CO2, CH4, N2O, in a tropical rainforest

Laëtitia Brechet1,2, Warren Daniel1,2, Clément Stahl2, Benoît Burban2, Jean-Yves Goret2, Roberto L. Salomόn3, and Ivan A. Janssens2
Laëtitia Brechet et al.
  • 1Centre of Excellence PLECO (Plants and Ecosystems), Department of Biology, University of Antwerp, Belgium
  • 2INRAE, UMR EcoFoG, CNRS, Cirad, AgroParisTech, Université des Antilles, Université de Guyane, French Guiana
  • 3Laboratory of Plant Ecology, Department of Applied Ecology and Environmental Biology, Ghent University, Belgium

The importance of greenhouse gas (GHG) emissions in global climate change is undisputed, but our understanding of the daily and seasonal variations of the GHG fluxes is far from complete and detailed flux estimates are unequally distributed among ecosystems worldwide. Carbon dioxide (77%; CO2), methane (14%; CH4) and nitrous oxide (8%; N2O) are the three main GHGs that trap infrared radiations and contribute to climate change. While CO2 has been largely studied, a considerable effort is still required to quantify the magnitude and drivers of CH4 and N2O, which have radiative effects 25 and 298 times greater than CO2, respectively. Tropical forests play a pivotal role in global carbon (C) balance and climate change mitigation, accounting for 68% of global C stock and representing up to 30% of total forest soil C sink. In the tropics, soils are main contributors to the ecosystem GHG fluxes. In fact, tropical forest soils are the largest natural source of soil CO2 and N2O and are overwhelmingly reported as important sink of CH4. More recently, studies reported that tree stems can also emit CO2, CH4 and N2O and act, via passive transport through the soil xylem stream, as a pathway for these gas emissions to the atmosphere.

Although accurate estimates of GHG sources and sinks are of great importance for reducing the uncertainties of C cycle - climate feed-backs, we are only just beginning to understand the role of tropical tree stems as producers and / or conduits of soil-produced GHG.

I present first results of soil and tree stem GHG fluxes estimated over a six-month period, including a dry and a wet season, of continuous high frequency measurements with automated GHG flux systems in a tropical rainforest, in French Guiana. We adapted and extended an existing soil GHG flux system, combining a commercial automated soil CO2 flux chamber system (LI-8100A) and CH4 and N2O analyser (Picarro G2308), to include tree stem chambers. Different closure times were applied to ensure reliable flux estimates, especially for low CH4 and N2O fluxes. I show that the new automated system operated successfully, allowing for robust long-term measurements to examine temporal variations and ultimately calculate budgets of CO2, CH4 and N2O fluxes at soil and tree stem levels. Our results indicated that soils and tree stems acted exclusively as source for CO2, whereas soils and tree stems exhibited distinct patterns for both CH4 and N2O, which highlights the importance of partitioning GHG fluxes to better determine environmental controls regulating ecosystem GHG exchanges.

How to cite: Brechet, L., Daniel, W., Stahl, C., Burban, B., Goret, J.-Y., Salomόn, R. L., and Janssens, I. A.: Towards a better understanding of soil- and tree stem-atmosphere exchanges of greenhouse gases, i.e. CO2, CH4, N2O, in a tropical rainforest, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11242,, 2020


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  • CC1: Comment on EGU2020-11242, Josep Barba, 07 May 2020

    Dear Laetitia,

    Many thanks for your presentation. Such an amazing study with interesting results coming from continuous measurements.

    I'd like to make a couple of comments:

    1) Have you run any temporal-series analysis to see if CH4 stem fluxes present diurnal cycles? That would bring some light on the origin of CH4 (i.g. diurnal cycles might be more related to water transport, and thus, soil origin, whereas non-diurnal cycles might suggest internal stem production)

    2) There is an open debate on which criterion we may use for QA/QC control on fluxes. However, if we are the Minimum Detectable Fluxes as a threshold for CH4 and N2O fluxes, we might be discarding all fluxes close to 0, inducing a bias in the data that might be relevant for cummulative flux calculations. You have one figure showing Soil N2O fluxes, and the area around 0 fluxes is clearly underpopulated. This might be the cause.

    Congrats for the nice study.

    Best regards,


    • AC1: Reply to CC1, Laëtitia Brechet, 07 May 2020

      Dear Josep,

      Thank you very much for your positive and constructive comments.

      1) This is a very good point and we have not yet fully explored the temporal variations in stem CH4 fluxes. Some interesting patterns emerged but further analyses are necessary to determine the origin of CH4 fluxes of our tropical tree. We also would like to perform some microbial analyses on the woody tissues.

      2) I agree, QA/QC control on CH4 and N2O fluxes are still debated. I have applied the MDF method on CH4 and N2O fluxes for this presentation but this is still exploratory data analysis. Also, measurements time for CH4 and N2O flux calculations is important to consider as can be different between soil and tree stem because of the lower fluxes in the stem compared with the soil. This is also something to test.

      I would be pleased to further discuss these aspects of the data analysis with you.

      Kind regards,


  • CC2: Comment on EGU2020-11242, Josep Barba, 08 May 2020

    We have defined (despite still under discussion) a QA/QC protocol. Feel free to reach me out if you want to discuss it. j.barbaferrer at

    • AC2: Reply to CC2, Laëtitia Brechet, 08 May 2020

      Thank you Josep; we will discuss about it by email.

  • CC3: Comment on EGU2020-11242, Nicholas Nickerson, 08 May 2020

    Great study and congratualations on getting such a nice continuous data set. Curious what you think the carious prodiction mecahnisms (or consumption) are for the gases. For example it looks like CH4 is being uptaken into the soil so presumably the postive flux from the tree is not soil related (unless its coming from a deep source of CH4 I suppose). 

    Another question is how much do you expect the xylem uptake of CO2 from the soil is affecting the overall soil flux measured? How do we decouple the two and is there some possibliltiy to use other gases or isotopes to seperate it further?

    • AC3: Reply to CC3, Laëtitia Brechet, 08 May 2020

      Dear Nicholas,

      Thank you very much for your nice comments.

      We only presented results for two soil chambers in this short video but there are more running in our field site (see Courtois et al. 2019), displaying large spatial and temporal variations in soil GHG fluxes. I would not affirm yet that our site act as sink of CH4, although it would work with the measured CH4 emissions in the tree stem. Longer period of measurements will certainly help understanding the origins of CH4 stem fluxes.

      Regarding your second point, we used CO2 probes to quantify the CO2 concentrations inside the tree stem, including xylem uptake of CO2 from the soil but more analyses have to be done on these data. I would be very interested in using isotope technique to disentangle sources of CO2, CH4 and N2O fluxes between and within ecosystem compartments of our tropical forest. This is something to develop.

      Kind regards,


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