Isotopic disequilibrium of the retro-diffusive CO2 efflux affects photosynthetic C18OO discrimination and the estimation of mesophyll conductance
2025
Huang, Sui Min | Ogée, Jérôme | Gong, Xiao Ying | Ma, Wei Ting | Li, Lei | Wang, Xuming | Schnyder, Hans | Schäufele, Rudi | Fujian Normal University [Fujian] | Interactions Sol Plante Atmosphère (UMR ISPA) ; Ecole Nationale Supérieure des Sciences Agronomiques de Bordeaux-Aquitaine (Bordeaux Sciences Agro)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE) | La Géometrie au Service du Numérique (GEOMERIX) ; Laboratoire d'informatique de l'École polytechnique [Palaiseau] (LIX) ; École polytechnique (X) ; Institut Polytechnique de Paris (IP Paris)-Institut Polytechnique de Paris (IP Paris)-Centre National de la Recherche Scientifique (CNRS)-École polytechnique (X) ; Institut Polytechnique de Paris (IP Paris)-Institut Polytechnique de Paris (IP Paris)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre Inria de l'Institut Polytechnique de Paris ; Centre Inria de Saclay ; Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria)-Centre Inria de Saclay ; Institut National de Recherche en Informatique et en Automatique (Inria)-Institut National de Recherche en Informatique et en Automatique (Inria) | Technische Universität Munchen - Technical University Munich - Université Technique de Munich (TUM)
International audience
Mostrar más [+] Menos [-]Inglés. Photosynthetic (COO)-O-18 fractionation (Delta O-18) has been used to estimate mesophyll conductance (g(m)) in C-3 and C-4 species. However, this requires knowledge of the degree of isotopic equilibration (theta(r)) between leaf water and the CO2 molecules penetrating the leaf interior and re-escaping without being assimilated (F-retro). Here, we re-examine the theory of Delta O-18-g(m) estimation and its sensitivity to changes in the O-18 composition (delta O-18) of CO2 on young and old leaves of six C-3 species. Our results showed that, when full isotopic equilibrium was assumed, g(m) values were sensitive to the delta O-18 of the CO2 sources. Utilizing a new isotopic mass balance model that distinguishes metabolic (R-t) and purely diffusive (F-retro) CO2 fluxes, we found that the gross H2O-equilibrated efflux (theta F-r(retro)+R-t) represented 157 +/- 12 % (mean +/- SE) of net CO2 assimilation, and was positively correlated to stomatal conductance, implying a limitation imposed by stomata. Furthermore, leaf water was not completely in equilibrium with F-retro (theta(r)<1) or the CO2 pool at the site of hydration (theta<1), which led to errors in estimated g(m). Our results have broad implications for the interpretation of Delta O-18 in terms of mesophyll conductance, and highlight the necessity of considering the isotopic disequilibrium of the retro-diffusive CO2 efflux.
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