title: (13) CO2 /(12) CO2 exchange fluxes in a clamp-on leaf cuvette: disentangling artefacts and flux components.
abstract: Leaks and isotopic disequilibria represent potential errors and artefacts during combined measurements of gas exchange and carbon isotope discrimination (Δ). This paper presents new protocols to quantify, minimize, and correct such phenomena. We performed experiments with gradients of CO2 concentration (up to ±250 μmol mol(-1) ) and δ(13) CCO2 (34‰), between a clamp-on leaf cuvette (LI-6400) and surrounding air, to assess (1) leak coefficients for CO2 , (12) CO2 , and (13) CO2 with the empty cuvette and with intact leaves of Holcus lanatus (C3 ) or Sorghum bicolor (C4 ) in the cuvette; and (2) isotopic disequilibria between net photosynthesis and dark respiration in light. Leak coefficients were virtually identical for (12) CO2 and (13) CO2 , but ∼8 times higher with leaves in the cuvette. Leaks generated errors on Δ up to 6‰ for H. lanatus and 2‰ for S. bicolor in full light; isotopic disequilibria produced similar variation of Δ. Leak errors in Δ in darkness were much larger due to small biological : leak flux ratios. Leak artefacts were fully corrected with leak coefficients determined on the same leaves as Δ measurements. Analysis of isotopic disequilibria enabled partitioning of net photosynthesis and dark respiration, and indicated inhibitions of dark respiration in full light (H. lanatus: 14%, S. bicolor: 58%).
authors.affiliation: Lehrstuhl für Grünlandlehre, Technische Universität München, 85354, Freising, Germany.
authors.forename: Xiao Ying
authors.identifier: http://orcid.org/0000-0002-4983-5645
authors.initials: XY
authors.lastname: Gong
authors.affiliation: Lehrstuhl für Grünlandlehre, Technische Universität München, 85354, Freising, Germany.
authors.forename: Rudi
authors.initials: R
authors.lastname: Schäufele
authors.affiliation: Lehrstuhl für Grünlandlehre, Technische Universität München, 85354, Freising, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Feneis
authors.affiliation: Lehrstuhl für Grünlandlehre, Technische Universität München, 85354, Freising, Germany.
authors.forename: Hans
authors.initials: H
authors.lastname: Schnyder
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D019069:Cell Respiration; D031752:Holcus / Q000378:metabolism*; D013058:Mass Spectrometry; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism; D045868:Sorghum / Q000378:metabolism*
chemical_list: D002245:Carbon Dioxide
keywords: CO2 transfer conductance; Li-Cor LI-6400; bundle sheath leakiness; diffusive leak; isotope ratio mass spectrometry; isotopic disequilibrium; labelling; mesophyll conductance; photosynthesis; respiration