First published online July 3, 2008; 10.1104/pp.108.123521
Plant Physiology 148:642-659 (2008)
© 2008 American Society of Plant Biologists
OPEN ACCESS ARTICLE
WHOLE PLANT AND ECOPHYSIOLOGY
Conifers, Angiosperm Trees, and Lianas: Growth, Whole-Plant Water and Nitrogen Use Efficiency, and Stable Isotope Composition ( 13C and 18O) of Seedlings Grown in a Tropical Environment1,[W],[OA]
Lucas A. Cernusak2,*,
Klaus Winter,
Jorge Aranda and
Benjamin L. Turner
Smithsonian Tropical Research Institute, Balboa, Ancon, Republic of Panama
Seedlings of several species of gymnosperm trees, angiosperm trees, and angiosperm lianas were grown under tropical field conditions in the Republic of Panama; physiological processes controlling plant C and water fluxes were assessed across this functionally diverse range of species. Relative growth rate, r, was primarily controlled by the ratio of leaf area to plant mass, of which specific leaf area was a key component. Instantaneous photosynthesis, when expressed on a leaf-mass basis, explained 69% of variation in r (P < 0.0001, n = 94). Mean r of angiosperms was significantly higher than that of the gymnosperms; within angiosperms, mean r of lianas was higher than that of trees. Whole-plant nitrogen use efficiency was also significantly higher in angiosperm than in gymnosperm species, and was primarily controlled by the rate of photosynthesis for a given amount of leaf nitrogen. Whole-plant water use efficiency, TEc, varied significantly among species, and was primarily controlled by ci/ca, the ratio of intercellular to ambient CO2 partial pressures during photosynthesis. Instantaneous measurements of ci/ca explained 51% of variation in TEc (P < 0.0001, n = 94). Whole-plant 13C discrimination also varied significantly as a function of ci/ca (R2 = 0.57, P < 0.0001, n = 94), and was, accordingly, a good predictor of TEc. The 18O enrichment of stem dry matter was primarily controlled by the predicted 18O enrichment of evaporative sites within leaves (R2 = 0.61, P < 0.0001, n = 94), with some residual variation explained by mean transpiration rate. Measurements of carbon and oxygen stable isotope ratios could provide a useful means of parameterizing physiological models of tropical forest trees.
1 This work was supported by the Smithsonian Tropical Research Institute. L.A.C. was supported by a postdoctoral fellowship from the Smithsonian Institution and a Tupper Research Fellowship from the Smithsonian Tropical Research Institute.
2 Present address: School of Environmental and Life Sciences, Charles Darwin University, Darwin, Northern Territory 0909, Australia.
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Lucas A. Cernusak (lucas.cernusak{at}cdu.edu.au).
[W] The online version of this article contains Web-only data.
[OA] Open Access article can be viewed online without a subscription.
www.plantphysiol.org/cgi/doi/10.1104/pp.108.123521
* Corresponding author; e-mail lucas.cernusak{at}cdu.edu.au.
Received May 26, 2008;
accepted June 23, 2008;
published July 3, 2008.
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