EGU25-21743, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-21743
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Stable isotopic characterization of CH4 emissions from tree stems in a central Amazon region 
Shujiro Komiya1, Santiago Botia1, Hella van Asperen1, Viviana Horna1, Hellen F. V. Cunha2, Jochen Schongart2, Maria Teresa Fernandez Piedade2, Florian Wittmann3, Daniel Magnabosco Marra1,4, Carina van der Veen5, Thomas Rockmann5, Susan Trumbore1, and Sam P. Jones1
Shujiro Komiya et al.
  • 1Max Planck Institute for Biogeochemistry, Jena, Germany (skomiya@bgc-jena.mpg.de)
  • 2Instituto Nacional de Pesquisas da Amazonia, INPA, Manaus, Brazil
  • 3Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 4Institute for Forest Protection, Julius Kühn Institute, Braunschweig, Germany
  • 5Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, The Netherlands

The vegetation and soils of the Amazon contain substantial amounts of carbon, with a portion of this carbon decomposing into methane (CH4) under anaerobic conditions. A significant quantity of the resultant CH4 is released into the atmosphere through tree stems. Given large variations in landscape and vegetation across the Amazon region, there remains a gap in our understanding of the distribution and influence of CH4 cycling processes (e.g., production, oxidation and transport) in the soil/water-trees-atmosphere continuum of Amazonian forest ecosystems. Natural abundance stable isotopes are powerful tracers of these processes but their application in the Amazon has so far been limited.

In this study, we report the results of carbon and hydrogen isotopic compositions of CH4 in gas samples obtained from different sources (e.g., stem chambers, stem boreholes, bubbles, soil gases, etc.) collected during three intensive field campaigns (two dry seasons: August 2022, September 2023, one wet season: March-April 2023). These campaigns were conducted in two different forest ecosystems (Igapo: seasonally flooded blackwater forest, Baixio: upland swamp valley forest) around the Amazon Tall Tower Observatory (ATTO) site, located in the intact central Amazon region. We conducted stem chamber sampling on 6-7 tree species at each forest site and collected stem borehole gas samples from CH4 hotspot trees and palms (Igapo: Macrolobium acaciifolium and Pouteria elegans, Baixio: Mauritia flexuosa). We estimated the source isotopic signatures of stem CH4 emission using the Keeling plot method. In addition, based on the three different campaigns, we investigated seasonal and inter-site variations in stem CH4 isotopic composition and also dual isotope relationships (δ13C-CH4 vs. δ2H-CH4, δ13C-CH4 vs. δ13C-CO2) to trace CH4 cycling processes in the soil/water-tree-atmosphere continuum.

The carbon isotopic signatures (δ13C-CH4) of stem CH4 emissions at the Baixio site ranged from -90 ‰ to -45 ‰, whereas the Igapo site displayed a range between -70 ‰ and -20 ‰. The δ13C-CH4 values of stem CH4 emissions from CH4 hotspot trees at the Igapo site were approximately 5-10 ‰ lighter than those of stem-borehole and bubble samples. This isotopic difference was mostly consistent across three term campaigns, indicating that diffusive isotopic fractionation by stem CH4 emissions of these tree species remains constant across seasons. In contrast, the isotopic differences in δ13C-CH4 between stem CH4 emissions and stem-borehole samples from CH4 hotspot trees at the Baixio site were approximately 20 ‰, which is approximately two times higher than at the Igapo site. The dual isotope relationships indicate that methane of the stem interior is predominantly derived from acetate fermentation in the Baixio site, whereas CH4 oxidation generates stable carbon isotopic signatures of the stem interior in the Igapo site. This study provides valuable insights into CH4 processes within the soil/water-tree-atmosphere continuum in the central Amazon rainforest, which would contribute to improving our process understanding and thus prediction of Amazonian CH4 budgets.

 

How to cite: Komiya, S., Botia, S., van Asperen, H., Horna, V., Cunha, H. F. V., Schongart, J., Piedade, M. T. F., Wittmann, F., Marra, D. M., van der Veen, C., Rockmann, T., Trumbore, S., and Jones, S. P.: Stable isotopic characterization of CH4 emissions from tree stems in a central Amazon region , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21743, https://doi.org/10.5194/egusphere-egu25-21743, 2025.