JXB Advance Access published online on October 29, 2003
Journal of Experimental Botany, doi:10.1093/jxb/erg309
© 2003 by Oxford University Press
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1 Departments of Crop Sciences and of Plant Biology, University of Illinois, Urbana-Champaign, 379 Edward R. Madigan Laboratory, 1201 W. Gregory Drive, Urbana, IL 61801, USA
* To whom correspondence should be addressed. E-mail: stevel{at}life.uiuc.edu.
The initial stimulation of photosynthesis observed on elevation of [CO2] in grasslands has been predicted to be a transient phenomenon constrained by the loss of photosynthetic capacity due to other limitations, notably nutrients and sinks for carbohydrates. Legumes might be expected partially to escape these feedbacks through symbiotic N2 fixation. The Free-Air Carbon dioxide Enrichment (FACE) experiment at Eschikon, Switzerland, has been the longest running investigation of the effects of open-air elevation of [CO2] on vegetation. The prediction of a long-term loss of photosynthetic capacity was tested by analysing photosynthesis in Trifolium repens L. (cv. Milkanova) in the spring and autumn of the eighth, ninth and tenth years of treatment. A high and low N treatment also allowed a test of the significance of exogenous N-supply in maintaining a stimulation of photosynthetic capacity in the long-term. Prior work in this Free Air CO2 Enrichment (FACE) experiment has revealed that elevated [CO2] increased both vegetative and reproductive growth of T. repens independent of N treatment. It is shown here that the photosynthetic response of T. repens was also independent of N fertilization under both current ambient and elevated (600 µmol mol-1) [CO2]. There was a strong effect of season on photosynthesis, with light-saturated rates (Asat) 37% higher in spring than in autumn. Higher Asat in the spring was supported by higher maximum Rubisco carboxylation rates (Vc,max) and maximum rates of electron transport (Jmax) contributing to RuBP regeneration. Elevated [CO2] increased Asat by 37% when averaged across all measurement periods and both N fertilization levels, and decreased stomatal conductance by 25%. In spring, there was no effect of elevated [CO2] on photosynthetic capacity of leaves, but in autumn both Vc,max and Jmax were reduced by approximately 20% in elevated [CO2]. The results show that acclimation of photosynthetic capacity can occur in a nitrogen-fixing species, in the field where there are no artificial restrictions on sink capacity. However, even with acclimation there was a highly significant increase in photosynthesis at elevated [CO2].
© 2003 Society for Experimental Biology
RESEARCH PAPER
Variation in acclimation of photosynthesis in Trifolium repens after eight years of exposure to Free Air CO2 Enrichment (FACE)
2 Departments of Crop Sciences and of Plant Biology, University of Illinois, Urbana-Champaign, 379 Edward R. Madigan Laboratory, 1201 W. Gregory Drive, Urbana, IL 61801, USA; Department of Environmental Sciences, Brookhaven National Laboratory, Upton, NY 11973-5000, USA
3 Institute of Plant Sciences, Swiss Federal Institute of Technology, 8092 Zürich, Switerland
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