AOBPreview originally published online on December 12, 2002
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Annals of Botany 91: 353-359, 2003
© 2003 Annals of Botany Company
Photosynthetic Induction and Leaf Carbon Gain in the Tropical Understorey Epiphyte, Aspasia principissa
1 Botanisches Institut der Universität Basel, Schönbeinstrasse 6, CH-4056 Basel, Switzerland, 2 Smithsonian Tropical Research Institute, Apdo 2072, Balboa, Panama and 3 Lehrstuhl für Botanik II der Universität Würzburg, D-97082 Würzburg, Germany
* For correspondence at: Botanisches Institut der Universität Basel, Schönbeinstrasse 6, CH-4056, Basel, Switzerland. Fax +41 61 267 35 04, e-mail gerhard.zotz{at}unibas.ch
Received: 2 August 2002; Returned for revision: 27 September 2002; Accepted: 25 October 2002 Published electronically: 12 December 2002
Gas exchange of the understorey epiphyte Aspasia principissa was studied in fluctuating light conditions both in the laboratory and in the field, testing the hypothesis that vascular epiphytes differ from most terrestrial understorey plants in showing a higher priority for water conservation. Consequently, a slow response of stomatal conductance to sudden increases in incident photon flux density (PFD) was expected, as was a fast loss of induction after such a light fleck. Results were only partly consistent with these expectations. Full induction of photosynthesis was indeed very slow and was not reached before, respectively, 40 and 60 min of saturating PFD in the field and the laboratory. In contrast, kinetics of induction loss were comparable with those of most terrestrial species studied to date. The overall impact of light flecks on in situ carbon gain again fulfilled expectations, being rather limited: the observed carbon gain was only approx. 66 % of the potential carbon gain estimated from a square-wave response model. It is concluded that in the drought-prone epiphytic habitat of a moist lowland forest, water conservation takes priority over carbon gain, which severely limits the use of light flecks for CO2 fixation in vascular epiphytes.
Key words: Aspasia principissa, Barro Colorado Island, epiphytes, induction, leaf carbon balance, light flecks, Orchidaceae, photosynthesis.
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