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Interacting effects of elevated CO2 and weather variability on photosynthesis of mature boreal Norway spruce agree with biochemical model predictions

Journal article
Authors Johan Uddling
Göran Wallin
Published in Tree Physiology
Volume 32
Issue 12
Pages 1509-1521
ISSN 0829-318X
Publication year 2012
Published at Department of Biological and Environmental Sciences
Pages 1509-1521
Language en
Keywords carbon dioxide, photosynthesis, Picea abies, respiration, stomatal conductance, whole-tree chambers
Subject categories Other Earth and Related Environmental Sciences, Botany, Terrestrial ecology


According to well-known biochemical and biophysical mechanisms, the stimulation of C3 photosynthesis by elevated atmospheric CO2 concentration ([CO2]) is strongly modified by changes in temperature and radiation. In order to investigate if a static parameterisation of the commonly used Farquhar et al. model of photosynthesis (i.e. without CO2-induced seasonal or thermal acclimation of photosynthetic capacity) can accurately predict these interactions in mature boreal Norway spruce (Picea abies (L.) Karst.) during the frost-free part of the growing season, shoot gas exchange was continuously measured on trees during their second/third year of exposure to ambient or doubled [CO2] inside whole-tree chambers. The relative CO2-induced enhancement of net photosynthesis (An) at a given temperature remained stable over the study period, but increased strongly with temperature and radiation, in agreement with predictions by the model. Light-saturated An (+67% at 20 C), dark respiration (+36%) and intercellular to ambient [CO2] ratio (ci/ca; +27%) were significantly increased by CO2 treatment. Stomatal conductance (gs) was not significantly affected. Our results demonstrate that the Farquhar et al. model of photosynthesis has the capability to predict interactions between [CO2] and seasonal weather variability on An in Norway spruce during the non-frost growing season without accounting for CO2-induced seasonal and/or thermal photosynthetic acclimation. However, stomatal model assumptions of reduced gs and constant ci/ca under rising atmospheric [CO2] did not hold.

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