title: The light response of mesophyll conductance is controlled by structure across leaf profiles.
abstract: Mesophyll conductance to CO2(gm) may respond to light either through regulated dynamic mechanisms or due to anatomical and structural factors. At low light, some layers of cells in the leaf cross-section approach photocompensation and contribute minimally to bulk leaf photosynthesis and little to whole leaf gm(gm,leaf). Thus, the bulk gm,leafwill appear to respond to light despite being based upon cells having an anatomically fixed mesophyll conductance. Such behaviour was observed in species with contrasting leaf structure using the variable J or stable isotope method of measuring gm,leaf. A species with bifacial structure, Arbutus × 'Marina', and an isobilateral species, Triticum durum L., had contrasting responses of gm,leafupon varying adaxial or abaxial illumination. Anatomical observations, when coupled with the proposed model of gm,leafto photosynthetic photon flux density (PPFD) response, successfully represented the observed gas exchange data. The theoretical and observed evidence that gm,leafapparently responds to light has large implications for how gm,leafvalues are interpreted, particularly limitation analyses, and indicates the importance of measuring gmunder full light saturation. Responses of gm,leafto the environment should be treated as an emergent property of a distributed 3D structure, and not solely a leaf area-based phenomenon.
authors.affiliation: Department of Plant Sciences, University of California, Davis, 95616, USA.
authors.forename: Guillaume
authors.identifier: http://orcid.org/0000-0002-2591-0524
authors.initials: G
authors.lastname: Théroux-Rancourt
authors.affiliation: Department of Plant Sciences, University of California, Davis, 95616, USA.
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Gilbert
mesh_terms: D003198:Computer Simulation; D029791:Ericaceae / Q000033:anatomy & histology* / Q000502:physiology / Q000528:radiation effects; D008027:Light; D058503:Mesophyll Cells / Q000502:physiology* / Q000528:radiation effects*; D008954:Models, Biological; D017785:Photons; D010788:Photosynthesis / Q000528:radiation effects; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000502:physiology / Q000528:radiation effects*; D015203:Reproducibility of Results; D014908:Triticum / Q000033:anatomy & histology* / Q000502:physiology / Q000528:radiation effects
keywords: Arbutus; Triticum; internal conductance; leaf anatomy; photosynthesis