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Two-Source δ 18 O Method to Validate the CO 18 O-Photosynthetic Discrimination Model: Implications for Mesophyll Conductance.
- Source :
-
Plant physiology [Plant Physiol] 2019 Nov; Vol. 181 (3), pp. 1175-1190. Date of Electronic Publication: 2019 Sep 13. - Publication Year :
- 2019
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Abstract
- Theoretical models of photosynthetic isotopic discrimination of CO <subscript>2</subscript> ( <superscript>13</superscript> C and <superscript>18</superscript> O) are commonly used to estimate mesophyll conductance ( g <subscript>m</subscript> ). This requires making simplifying assumptions and assigning parameter values so that g <subscript>m</subscript> can be solved for as the residual term. Uncertainties in g <subscript>m</subscript> estimation occur due to measurement noise and assumptions not holding, including parameter uncertainty and model parametrization. Uncertainties in the <superscript>13</superscript> C model have been explored previously, but there has been little testing undertaken to determine the reliability of g <subscript>m</subscript> estimates from the <superscript>18</superscript> O model ( g <subscript>m18</subscript> ). In this study, we exploited the action of carbonic anhydrase in equilibrating CO <subscript>2</subscript> with leaf water and manipulated the observed photosynthetic discrimination (Δ <superscript>18</superscript> O) by changing the oxygen isotopic composition of the source gas CO <subscript>2</subscript> and water vapor. We developed a two-source δ <superscript>18</superscript> O method, whereby two measurements of Δ <superscript>18</superscript> O were obtained for a leaf with its gas-exchange characteristics otherwise unchanged. Measurements were performed in broad bean ( Vicia faba ) and Algerian oak ( Quercus canariensis ) in response to light and vapor pressure deficit. Despite manipulating the Δ <superscript>18</superscript> O by over 100‰, in most cases we observed consistency in the calculated g <subscript>m18</subscript> , providing confidence in the measurements and model theory. Where there were differences in g <subscript>m18</subscript> estimates between source-gas measurements, we explored uncertainty associated with two model assumptions (the isotopic composition of water at the sites of CO <subscript>2</subscript> -water exchange, and the humidity of the leaf internal airspace) and found evidence for both. Finally, we provide experimental guidelines to minimize the sensitivity of g <subscript>m18</subscript> estimates to measurement errors. The two-source δ <superscript>18</superscript> O method offers a flexible tool for model parameterization and provides an opportunity to refine our understanding of leaf water and CO <subscript>2</subscript> fluxes.<br /> (© 2019 American Society of Plant Biologists. All Rights Reserved.)
Details
- Language :
- English
- ISSN :
- 1532-2548
- Volume :
- 181
- Issue :
- 3
- Database :
- MEDLINE
- Journal :
- Plant physiology
- Publication Type :
- Academic Journal
- Accession number :
- 31519787
- Full Text :
- https://doi.org/10.1104/pp.19.00633