Light distribution in leaf chambers and its consequences for photosynthesis measurements |
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Authors: | S W Hogewoning G Trouwborst J Harbinson W Van Ieperen |
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Institution: | (1) Department of Botany, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI 53706, USA;(2) Department of Biochemistry and Molecular Biology, Michigan State University, 410 Biochemistry Building, East Lansing, MI 48824-1319, USA; |
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Abstract: | The impact of a heterogeneous distribution of actinic light within a leaf chamber for photosynthetic measurements by gas exchange
on the photosynthesis-irradiance relationship was investigated. High-resolution light distributions were measured over the
area of a commercially available clamp-on leaf chamber equipped with build-in red and blue LEDs, as well as over the area
of a custom-made leaf chamber with external light source, using a low-cost digital camera and freely available software. The
impact of the measured heterogeneity on the photosynthesis-irradiance response curve was calculated for two realistic scenarios.
When the average light intensity over the leaf chamber area was estimated accurately, heterogeneity had minor effects on the
photosynthesis-irradiance response curve. However, when the irradiance was measured in the chamber centre, which is common
practice, and assumed to be homogeneous, for both leaf chambers the photosynthesis-irradiance response curve was subject to
considerable error and led to serious underestimation of the light-limited quantum yield of photosynthesis. Additionally,
mixed light sources with different heterogeneity patterns per light source, such as in the clamp-on leaf chamber, potentially
increase errors due to heterogeneous physiological responses to light spectrum. High-resolution quantification of the leaf-chamber
light distribution enables calculation of the correct average light intensity and already resolves the most pressing problems
associated with heterogeneity. To exclude any light-distribution related errors in gas-exchange measurements a leaf chamber
and actinic irradiance source design with a homogeneous light distribution is an absolute requirement. |
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