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JXB Advance Access published online on July 4, 2006
Journal of Experimental Botany, doi:10.1093/jxb/erl003
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© 2006 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Received January 26, 2006
Accepted March 28, 2006

RESEARCH PAPER

Air pressure in clamp-on leaf chambers: a neglected issue in gas exchange measurements

Siegfried Jahnke 1 * and Roland Pieruschka 2

1 Forschungszentrum Jülich GmbH, Institut für Chemie und Dynamik der Geosphäre, ICG-III: Phytosphäre, D-52425 Jülich, Germany; Universität Duisburg-Essen, FB Biologie und Geographie, Institut für Biologie, D-45117 Essen, Germany
2 Forschungszentrum Jülich GmbH, Institut für Chemie und Dynamik der Geosphäre, ICG-III: Phytosphäre, D-52425 Jülich, Germany

* To whom correspondence should be addressed.
Siegfried Jahnke, E-mail: s.jahnke{at}fz-juelich.de


  Abstract

Air pressure in leaf chambers is thought to affect gas exchange measurements through changes in partial pressure of the air components. However, other effects may come into play when homobaric leaves are measured in which internal lateral gas flow may occur. When there was no pressure difference between the leaf chamber and ambient air ({Delta}P=0), it was found in previous work that lateral CO2 diffusion could affect measurements performed with clamp-on leaf chambers. On the other hand, overpressure ({Delta}P>0) in leaf chambers has been reported to minimize artefacts possibly caused by leaks in chamber sealing. In the present work, net CO2 exchange rates (NCER) were measured under different {Delta}P values (0.0-3.0 kPa) on heterobaric and homobaric leaves. In heterobaric leaves which have internal barriers for lateral gas movement, changes in {Delta}P had no significant effect on NCER. For homobaric leaves, effects of {Delta}P>0 on measured NCER were significant, obviously due to lateral gas flux inside the leaf mesophyll. The magnitude of the effect was largely defined by stomatal conductance; when stomata were widely open, the impact of {Delta}P on measured NCER was up to 7 µmol CO2 m-2 s-1 kPa-1. Since many other factors are also involved, neither {Delta}P=0 nor {Delta}P>0 was found to be the ‘one-size fits all’ solution to avoid erroneous effects of lateral gas transport on measurements with clamp-on leaf chambers.

Keywords: Air pressure; clamp-on leaf chamber; gas exchange measurement; homobaric leaves; respiration; photosynthesis; transpiration.
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