Adjustments in epidermal UV-transmittance of leaves in sun-shade transitions

Authors

  • Paul W. Barnes,

    Corresponding author
    • Department of Biological Sciences, Loyola University New Orleans, New Orleans, LA, USA
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  • Anna R. Kersting,

    1. Lehrstuhl für experimentelle Ökologie und Ökosystembiologie, Universität Bielefeld, Universitätsstrasse 25, Bielefeld, Germany
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    • Present address: Bioinformatics, Heinrich-Heine Universität Düsseldorf, Universitätsstrasse 1, 40225 Düsseldorf, Germany

  • Stephan D. Flint,

    1. Department of Wildland Resources, Utah State University, Logan, UT, USA
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    • Present address: Department of Forest, Rangeland and Fire Sciences, UIPO 441135, University of Idaho, Moscow, ID 83844-1135 USA

  • Wolfram Beyschlag,

    1. Lehrstuhl für experimentelle Ökologie und Ökosystembiologie, Universität Bielefeld, Universitätsstrasse 25, Bielefeld, Germany
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  • Ronald J. Ryel

    1. Department of Wildland Resources, Utah State University, Logan, UT, USA
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Correspondence

Corresponding author,

e-mail: pwbarnes@loyno.edu

Abstract

Epidermal UV transmittance (TUV) and UV-absorbing compounds were measured in sun and shade leaves of Populus tremuloides and Vicia faba exposed to contrasting light environments under field conditions to evaluate UV acclimation potentials and regulatory roles of photosynthetically active radiation (PAR) and UV in UV-shielding. Within a natural canopy of Ptremuloides, TUV ranged from 4 to 98% and showed a strong nonlinear relationship with mid-day horizontal fluxes of PAR [photon flux density (PFD) = 6–1830 µmol m−2 s−1]; similar patterns were found for V. faba leaves that developed under a comparable PFD range. A series of field transfer experiments using neutral-density shade cloth and UV blocking/transmitting films indicated that PAR influenced TUV during leaf development to a greater degree than UV, and shade leaves of both species increased their UV-shielding when exposed to full sun; however, this required the presence of UV, with both UV-A and UV-B required for full acclimation. TUV of sun leaves of both species was largely unresponsive to shade either with or without UV. In most, but not all cases, changes in TUV were associated with alterations in the concentration of whole-leaf UV-absorbing compounds. These results suggest that, (1) moderate-to-high levels of PAR alone during leaf development can induce substantial UV-protection in field-grown plants, (2) mature shade leaves have the potential to adjust their UV-shielding which may reduce the detrimental effects of UV that could occur following sudden exposures to high light and (3) under field conditions, PAR and UV play different roles in regulating UV-shielding during and after leaf development.

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