title: Spatial distribution of leaf nitrogen and photosynthetic capacity within the foliage of individual trees: disentangling the effects of local light quality, leaf irradiance, and transpiration.
abstract: There is presently no consensus about the factor(s) driving photosynthetic acclimation and the intra-canopy distribution of leaf characteristics under natural conditions. The impact was tested of local (i) light quality (red/far red ratio), (ii) leaf irradiance (PPFD(i)), and (iii) transpiration rate (E) on total non-structural carbohydrates per leaf area (TNC(a)), TNC-free leaf mass-to-area ratio (LMA), total leaf nitrogen per leaf area (N(a)), photosynthetic capacity (maximum carboxylation rate and light-saturated electron transport rate), and leaf N partitioning between carboxylation and bioenergetics within the foliage of young walnut trees grown outdoors. Light environment (quantity and quality) was controlled by placing individual branches under neutral or green screens during spring growth, and air vapour pressure deficit (VPD) was prescribed and leaf transpiration and photosynthesis measured at branch level by a branch bag technique. Under similar levels of leaf irradiance, low air vapour pressure deficit decreased transpiration rate but did not influence leaf characteristics. Close linear relationships were detected between leaf irradiance and leaf N(a), LMA or photosynthetic capacity, and low R/FR ratio decreased leaf N(a), LMA and photosynthetic capacity. Irradiance and R/FR also influenced the partitioning of leaf nitrogen into carboxylation and electron light transport. Thus, local light level and quality are the major factors driving photosynthetic acclimation and intra-canopy distribution of leaf characteristics, whereas local transpiration rate is of less importance.
authors.affiliation: UMR-PIAF Integrated Tree Physiology, INRA-University Blaise Pascal, 234 avenue du Brézet, F-63039 Clermont-Ferrand Cedex 02, France. frak@clermont.inra.fr
authors.forename: Ela
authors.initials: E
authors.lastname: Frak
authors.forename: Xavier
authors.initials: X
authors.lastname: Le Roux
authors.forename: Peter
authors.initials: P
authors.lastname: Millard
authors.forename: Boris
authors.initials: B
authors.lastname: Adam
authors.forename: Erwin
authors.initials: E
authors.lastname: Dreyer
authors.forename: Cynthia
authors.initials: C
authors.lastname: Escuit
authors.forename: Hervé
authors.initials: H
authors.lastname: Sinoquet
authors.forename: Marc
authors.initials: M
authors.lastname: Vandame
authors.forename: Claude
authors.initials: C
authors.lastname: Varlet-Grancher
mesh_terms: D000064:Acclimatization / Q000502:physiology / Q000528:radiation effects; D001692:Biological Transport / Q000502:physiology / Q000528:radiation effects; D050260:Carbohydrate Metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D008027:Light; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D018515:Plant Leaves / Q000502:physiology* / Q000528:radiation effects; D018547:Plant Stems / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology* / Q000528:radiation effects; D014197:Trees / Q000502:physiology* / Q000528:radiation effects; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water; D002245:Carbon Dioxide; D009584:Nitrogen