Leaf-scale quantification of the effect of photosynthetic gas exchange on Δ17O of atmospheric CO2
- 1Utrecht University, Institute for Marine and Atmospheric Research Utrecht (IMAU), Physics and Astronomy, Utrecht, Netherlands (email@example.com, firstname.lastname@example.org )
- 2University of Utrecht, Institute of Environmental Biology, Utrecht, The Netherlands (T.L.Pons@uu.nl)
- 3Department of Meteorology and Air Quality, Wageningen University, The Netherlands (email@example.com, Wouter.Peters@wur.nl)
- 4Centre for Isotope Research, University of Groningen, The Netherlands (Wouter.Peters@wur.nl)
Understanding the processes affecting the triple oxygen isotope composition of atmospheric CO2 during photosynthesis can help to constrain the interaction and fluxes between the atmosphere and the biosphere. We conducted leaf cuvette experiments under controlled conditions, using sunflower (Helianthus annuus), an annual C3 species with high photosynthetic capacity and stomatal conductance for CO2, an evergreen C3 species, ivy (Hedera hybernica) with lower values for these traits, and a C4 species maize (Zea mays) that has a high photosynthetic capacity and low stomatal conductance. The experiments were conducted at different light intensities and using CO2 with different 17O- excess. Our results demonstrate that two key factors determine the effect of photosynthetic gas exchange on Δ17O of atmospheric CO2: The relative difference in Δ17O of the CO2 entering the leaf and Δ17O of leaf water, and the back-diffusion flux from the leaf to the atmosphere, which can be quantified by the cm/ca ratio. At low cm/ca the discrimination is governed by diffusion into the leaf, and at high cm/ca by back-diffusion of CO2 that has equilibrated with the leaf water. Plants with a higher cm/ca ratio modify the Δ17O of atmospheric CO2 more strongly than plants with lower cm/ca.
Based on the leaf cuvette experiments using both C4 and C3 plants, the global discrimination in 17O-excess of atmospheric CO2 due to assimilation is estimated to be -0.6±0.2‰. The main uncertainty in the global estimation is due to the uncertainty in the cm/ca ratio.
How to cite: Adnew, G., Pons, T., Koren, G., Peters, W., and Röckmann, T.: Leaf-scale quantification of the effect of photosynthetic gas exchange on Δ17O of atmospheric CO2 , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3064, https://doi.org/10.5194/egusphere-egu2020-3064, 2020
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