Lateral diffusion of CO2 from shaded to illuminated leaf parts affects photosynthesis inside homobaric leaves

Authors

  • Roland Pieruschka,

    1. Forschungszentrum Jülich GmbH, Institut für Chemie und Dynamik der Geosphäre (ICG), Institut III: Phytosphäre, 52425 Jülich, Germany;
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  • Ulrich Schurr,

    1. Forschungszentrum Jülich GmbH, Institut für Chemie und Dynamik der Geosphäre (ICG), Institut III: Phytosphäre, 52425 Jülich, Germany;
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  • Manfred Jensen,

    1. Universität Duisburg-Essen, FB Biologie und Geographie, Institut für Biologie, Allgemeine Botanik, 45117 Essen, Germany
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  • Wilfried F. Wolff,

    1. Forschungszentrum Jülich GmbH, Institut für Chemie und Dynamik der Geosphäre (ICG), Institut III: Phytosphäre, 52425 Jülich, Germany;
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  • Siegfried Jahnke

    1. Forschungszentrum Jülich GmbH, Institut für Chemie und Dynamik der Geosphäre (ICG), Institut III: Phytosphäre, 52425 Jülich, Germany;
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Author for correspondence: Siegfried Jahnke Tel: +49 2461618681 Fax: +49 2461612492 Email: s.jahnke@fz-juelich.de

Summary

  • • Gas exchange is generally regarded to occur between the leaf interior and ambient air, i.e. in vertical (anticlinal) directions of leaf blades. However, inside homobaric leaves, gas movement occurs also in lateral directions. The aim of the present study was to ascertain whether lateral CO2 diffusion affects leaf photosynthesis when illuminated leaves are partially shaded.
  • • Measurements using gas exchange and chlorophyll fluorescence imaging techniques were performed on homobaric leaves of Vicia faba and Nicotiana tabacum or on heterobaric leaves of Glycine max and Phaseolus vulgaris.
  • • For homobaric leaves, gas exchange inside a clamp-on leaf chamber was affected by shading the leaf outside the chamber. The quantum yield of photosystem II (ΦPSII) was highest directly adjacent to a light/shade border (LSB). ΦPSII decreased in the illuminated leaf parts with distance from the LSB, while the opposite was observed for nonphotochemical quenching. These effects became most pronounced at low stomatal conductance. They were not observed in heterobaric leaves.
  • • The results suggest that plants with homobaric leaves can benefit from lateral CO2 flux, in particular when stomata are closed (e.g. under drought stress). This may enhance photosynthetic, instead of nonphotochemical, processes near LSBs in such leaves and reduce the photoinhibitory effects of excess light.

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