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JXB Advance Access published online on June 1, 2009
Journal of Experimental Botany, doi:10.1093/jxb/erp149
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© 2009 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

Canopy CO2 exchange of two neotropical tree species exhibiting constitutive and facultative CAM photosynthesis, Clusia rosea and Clusia cylindrica

Klaus Winter1,*, Milton Garcia1 and Joseph A. M. Holtum2

1Smithsonian Tropical Research Institute, PO Box 0843-03092, Balboa, Ancon, Republic of Panama
2School of Marine and Tropical Biology, James Cook University, Townsville, Queensland 4811, Australia

* To whom correspondence should be addressed. E-mail: winterk{at}si.edu

Photon flux density (PFD) and water availability, the daily and seasonal factors that vary most in tropical environments, were examined to see how they influenced expression of crassulacean acid metabolism (CAM) in 3-year-old Clusia shrubs native to Panama. Instead of the commonly used single-leaf approach, diel CO2 exchange was measured for whole individual canopies of plants in large soil containers inside a naturally illuminated 8.8 m3 chamber. In well-watered C. rosea, a mainly constitutive CAM species, nocturnally fixed CO2 contributed about 50% to 24 h carbon gain on sunny days but the contribution decreased to zero following overcast days. Nonetheless, CO2 fixation in the light responded in such a way that 24 h carbon gain was largely conserved across the range of daily PFDs. The response of C. rosea to drought was similarly buffered. A facultative component of CAM expression led to reversible increases in nocturnal carbon gain that offset drought-induced reductions of CO2 fixation in the light. Clusia cylindrica was a C3 plant when well-watered but exhibited CAM when subjected to water stress. The induction of CAM was fully reversible upon rewatering. C. cylindrica joins C. pratensis as the most unambiguous facultative CAM species reported in the genus Clusia.

Key words: Clusia cylindrica, Clusia rosea, CO2 exchange, constitutive CAM, crassulacean acid metabolism, facultative CAM, photosynthetic pathway, tree canopy, whole-plant physiology

Received 6 March 2009; Revised 7 April 2009 Accepted 16 April 2009


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