title: Diurnal pattern of stomatal conductance in the large-leaved temperate liana Aristolochia macrophylla depends on spatial position within the leaf lamina.
abstract: OBJECTIVE
  The large distance between peripheral leaf regions and the petiole in large leaves is expected to cause stronger negative water potentials at the leaf apex and marginal zones compared with more central or basal leaf regions. Leaf zone-specific differences in water supply and/or gas exchange may therefore be anticipated. In this study, an investigation was made to see whether zonal differences in gas exchange regulation can be detected in large leaves.
  
  
  METHODS
  The diurnal course of stomatal conductance, gs, was monitored at defined lamina zones during two consecutive vegetation periods in the liana Aristolochia macrophylla that has large leaves. Local climate and stem water potential were also monitored to include parameters involved in stomatal response. Additionally, leaf zonal vein densities were measured to assess possible trends in local hydraulic supply.
  
  
  RESULTS
  It was found that the diurnal pattern of gs depends on the position within a leaf in A. macrophylla. The highest values during the early morning were shown by the apical region, with subsequent decline later in the morning and a further gradual decline towards the evening. The diurnal pattern of gs at the marginal regions was similar to that of the leaf tip but showed a time lag of about 1 h. At the leaf base, the diurnal pattern of gs was similar to that of the margins but with lower maximum gs. At the the leaf centre regions, gs tended to show quite constant moderate values during most of the day. Densities of minor veins were lower at the margin and tip compared with the centre and base.
  
  
  CONCLUSIONS
  Gas exchange regulation appears to be zone specific in A. macrophylla leaves. It is suggested that the spatial-diurnal pattern of gs expressed by A. macrophylla leaves represents a strategy to prevent leaf zonal water stress and subsequent vein embolism.
authors.affiliation: Department of Geosciences, University of Tübingen, Sigwartstr. 10, D-72076 Tübingen, Germany.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Miranda
authors.forename: Martin
authors.initials: M
authors.lastname: Ebner
authors.forename: Christopher
authors.initials: C
authors.lastname: Traiser
authors.forename: Anita
authors.initials: A
authors.lastname: Roth-Nebelsick
mesh_terms: D030022:Aristolochia / Q000254:growth & development / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D002980:Climate; D017753:Ecosystem; D009995:Osmosis; D017785:Photons; D010788:Photosynthesis; D018547:Plant Stems / Q000502:physiology; D054046:Plant Stomata / Q000502:physiology*; D058526:Plant Vascular Bundle / Q000502:physiology; D055548:Vapor Pressure; D014867:Water
chemical_list: D014867:Water