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Journal of Experimental Botany 2007 58(15-16):4293-4306; doi:10.1093/jxb/erm313
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© 2007 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

Temperature dependency of bark photosynthesis in beech (Fagus sylvatica L.) and birch (Betula pendula Roth.) trees

Christiane Wittmann and Hardy Pfanz*

Institute of Applied Botany, University of Duisburg-Essen, D-45117 Essen, Germany

* To whom correspondence should be addressed. E-mail: hardy.pfanz{at}uni-essen.de

Temperature dependencies of stem dark respiration (Rd) and light-driven bark photosynthesis (Amax) of two temperate tree species (Fagus sylvatica and Betula pendula) were investigated to estimate their probable influence on stem carbon balance. Stem Rd was found to increase exponentially with increasing temperatures, whereas Amax levelled off or decreased at the highest temperatures chosen (35–40 °C). Accordingly, a linear relationship between respiratory and assimilatory metabolism was only found at moderate temperatures (10–30 °C) and the relationship between stem Rd and Amax clearly departed from linearity at chilling (5 °C) and at high temperatures (35–40 °C). As a result, the proportional internal C-refixation rate also decreased non-linearly with increasing temperature. Temperature response of photosystem II (PSII) photochemistry was also assessed. Bark photochemical yield ({Delta}F/Fm') followed the same temperature pattern as bark CO2 assimilation. Maximum quantum yield of PSII (Fv/Fm) decreased drastically at freezing temperatures (–5 °C), while from 30 to 40 °C only a marginal decrease in Fv/Fm was found. In in situ measurements during winter months, bark photosynthesis was found to be strongly reduced. Low temperature stress induced an active down-regulation of PSII efficiency as well as damage to PSII due to photoinhibition. All in all, the benefit of bark photosynthesis was negatively affected by low (<5 °C) as well as high temperatures (>30 °C). As the carbon balance of tree stems is defined by the difference between photosynthethic carbon gain and respiratory carbon loss, this might have important implications for accurate modelling of stem carbon balance.

Key words: Beech, birch, CO2 exchange, fluorescence, stem photosynthesis, stem respiration, temperature response

Received 13 June 2007; Revised 25 October 2007 Accepted 29 October 2007


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