JXB Advance Access originally published online on July 4, 2006
Journal of Experimental Botany 2006 57(11):2553-2561; 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.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Air pressure in clamp-on leaf chambers: a neglected issue in gas exchange measurements
1Forschungszentrum Jülich GmbH, Institut für Chemie und Dynamik der Geosphäre, ICG-III: Phytosphäre, D-52425 Jülich, Germany
2Universität Duisburg-Essen, FB Biologie und Geographie, Institut für Biologie, D-45117 Essen, Germany
*To whom correspondence should be addressed. E-mail: s.jahnke{at}fz-juelich.de
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 (
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 (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 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 P had no significant effect on NCER. For homobaric leaves, effects of 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 P on measured NCER was up to 7 µmol CO2 m–2 s–1 kPa–1. Since many other factors are also involved, neither P=0 nor 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.
Key words: Air pressure, clamp-on leaf chamber, gas exchange measurement, homobaric leaves, respiration, photosynthesis, transpiration
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