Articles | Volume 23, issue 14
https://doi.org/10.5194/bg-23-5163-2026
https://doi.org/10.5194/bg-23-5163-2026
Research article
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28 Jul 2026
Research article | Highlight paper |  | 28 Jul 2026

CO2 and H2O isotope exchange and flux partitioning in Amazonia

Robbert P. J. Moonen, Getachew A. Adnew, Jordi Vilà-Guerau de Arellano, David J. Bonell Fontas, and Thomas Röckmann

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Cited articles

Adnew, G. A., Pons, T. L., Koren, G., Peters, W., and Röckmann, T.: Leaf-scale quantification of the effect of photosynthetic gas exchange on Δ17O of atmospheric CO2, Biogeosciences, 17, 3903–3922, https://doi.org/10.5194/bg-17-3903-2020, 2020. a, b, c
Adnew, G. A., Hofmann, M. E., Pons, T. L., Koren, G., Ziegler, M., Lourens, L. J., and Röckmann, T.: Leaf scale quantification of the effect of photosynthetic gas exchange on Δ47 of CO2, Sci. Rep., 11, https://doi.org/10.1038/s41598-021-93092-0, 2021. a
Artaxo, P.: Amazon deforestation implications in local/regional climate change, P. Natl. Acad. Sci. USA, 120, https://doi.org/10.1073/pnas.2317456120, 2023. a
Baldocchi, D. D.: Measuring fluxes of trace gases and energy between ecosystems and the atmosphere – the state and future of the eddy covariance method, Glob. Change Biol., 20, 3600–3609, https://doi.org/10.1111/gcb.12649, 2014. a, b
Barbour, M. M. and Farquhar, G. D.: Do pathways of water movement and leaf anatomical dimensions allow development of gradients in H218O between veins and the sites of evaporation within leaves?, Plant Cell Environ., 27, 107–121, https://doi.org/10.1046/j.0016-8025.2003.01132.x, 2004. a, b
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Editorial statement
The study presents the first simultaneous in-situ eddy covariance measurements of CO₂ and H₂O isotopologue fluxes above an Amazonian rainforest canopy. Using δ¹⁸O as a shared tracer, the authors reconstruct a coherent isotopic cascade linking soil, xylem, leaf, canopy, and atmosphere for both water and carbon dioxide, and demonstrate that the two isotopic states are physically consistent at the leaf evaporative sites where they intersect. This allows the elusive gross components of net exchange to be resolved: transpiration accounts for 95.5% of evapotranspiration, while photosynthesis (144% of NEE) and soil respiration (-44%) are separated. As the Amazon shifts from carbon sink toward source, such methods offer a valuable route to disentangle carbon–water coupling.
Short summary
We used high-frequency H₂O and CO₂ isotope measurements taken in the Amazon Tall Tower Observatory (ATTO) to separate water vapour and carbon dioxide fluxes into their component processes. During midday, ~95 % of evapotranspiration came from plant transpiration. Isotopes also revealed the balance between photosynthesis and respiration, showing strong sensitivity to leaf CO₂ ratios. These results improve understanding of Amazon ecosystem function.
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