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The Influence of Epidermal Windows on the Light Environment Within the Leaves of Six Succulents
Egbert, Kathryn J. Martin, Craig E. Vogelmann, Thomas C.
Egbert, Kathryn J.
Martin, Craig E.
Vogelmann, Thomas C.
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Abstract
An omni-directional fibre optic microprobe was used
to measure the quantity and quality of light within the
leaves of six succulents having epidermal windows,
three species having a subterranean growth habit
(Haworthia truncata, Lithops olivacea, and Opthalmophyllum
longum) and three growing above ground
(Peperomia dolabriformis, P. graveolens, and the
sprawling vine Senecio rowleyanus). Although light
levels at most locations inside the leaves of all species
were high, near those incident on the window surfaces,
light levels inside the leaves of the two species of
Peperomia often greatly exceeded incident light levels,
indicating considerable light scattering and focusing
by the leaf tissue. The spectral quality of light inside
the leaves of all taxa reflected the absorption properties
of chlorophyll, with most of the photons in the
green wavelengths. Light quality and quantity inside
the leaves did not correlate with the growth habit of the
plants, the size of the window (as a proportion of the
total leaf area), or location inside the leaf, although
light levels generally declined and wavelengths increased
deeper in the leaves. Application of reflective
tape to the windows reduced internal light levels in
L. olivacea and S. rowleyanus, although reductions
were not always statistically significant. Although light
levels throughout the leaves of P. graveolens were
substantially and significantly reduced as a result of
the application of reflective tape to its windows, the
light levels even at the basal chlorenchyma on the
abaxial side of the leaf remained high. In all species
investigated, the levels of near-infrared radiation inside
the leaves were surprisingly high, yet also declined
deeper inside the succulent leaves. This nearinfrared
radiation may add to the heat load of these
* To whom correspondence should be addressed. E-mail: ecophys@ku.edu
plants. Furthermore, application of reflective tape to
the windows also reduced the amount of near-infrared
radiation inside the leaves of the three succulents
examined. These results led to a novel, testable
hypothesis that may help to explain previous findings
that application of reflective tape to the windows of the
leaves of these succulents did not effect a reduction in
photosynthetic activity.
Description
This is the publisher's official version. It is also available electronically from: http://dx.doi.org/10.1093/jxb/ern105.
Date
2008
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Oxford University Press
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Keywords
Chlorenchyma, Haworthia truncata, hydenchyma, infrared radiation, internal light environment, leaf windows, light focusing and scattering, Lithops olivacea, omni-directional fibre optic microprobe, Peperomia dolabriformis, Peperomia graveolens, Opthalmophyllum longum, photon flux density, Senecio rowleyanus, succulents, visible radiation
Citation
Egbert, K.J., C. E. Martin, and T.C. Vogelmann. 2008. The influence of epidermal
windows on the light environment within the leaves of six succulents. J. Exp. Bot. 59:1863-1873. http://dx.doi.org/10.1093/jxb/ern105