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First published online July 20, 2009; doi:10.3732/ajb.0800420 American Journal of Botany 96: 1454-1461 (2009) © 2009 Botanical Society of America, Inc. |
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Ecology |
2 Departamento de Biología Vegetal I, Universidad Complutense de Madrid. José Antonio Novais 2 28040 Madrid, Spain 3 Centro de Ciencias Medioambientales, CSIC, Serrano 115 Dpdo. 28006 Madrid, Spain 4 Department of Biology, Duke University, Box 90338 Durham, North Carolina 27708 USA
ABSTRACT
Woody plants, as sessile and long-lived organisms, are expected to have effective mechanisms for dealing with recurrent environmental stresses. In the present study, we hypothesized that phenotypic plasticity (the ability to express alternative phenotypes) and integration (covariation among functionally related traits) are elicited in plants under stressful wind speed conditions. We investigated the within-crown variation of nine vegetative traits of a tree species (Olea europaea subsp. guanchica) in six populations that represented a gradient of wind speed exposures. Wind-exposed twigs in outer-canopy layers had smaller leaves; thinner, lighter, and shorter internodes; and a larger internode cross-sectional area to leaf area ratio. Comparison between field and greenhouse trials revealed that field differences among populations were mediated by phenotypic plasticity. Outer-canopy twigs expressed plastic responses in populations exposed to high wind speeds, whereas inner-canopy twigs displayed high phenotypic convergence among populations. In addition, phenotypic integration increased with wind exposure (outer canopy > inner canopy > greenhouse) and was consequently affected by canopy openness. We conclude that exposure to wind above a certain speed threshold in this woody species elicits a plastic response that is associated with increased integration among traits and involves mechanical and hydraulic rearrangements in more exposed parts of the trees.
Key Words: Canary Islands • canopy openness • environmental stress • internode size • intracanopy plasticity • Olea europaea • Oleaceae
Received for publication 15 December 2008. Accepted for publication 15 April 2009.
FOOTNOTES
1 This research was funded by the Spanish Ministerio de Educación y Ciencia (project CGL2005-03062/BOS: Procesos y mecanismos evolutivos en Olea europaea L.), by the Comunidad de Madrid (project REMEDINAL, S-0505/AMB/0335) and by an FPU grant to C.G.-V. (AP-2004-3448). The authors are thankful for facilities provided by the "Cabildo de Tenerife" at La Tahonilla nursery. S. Pérez García (Canarian Institute of Technology, ITC) provided valuable wind data. They acknowledge the contribution of M.E. Pérez-Corona in an early phase of the study, the help of M. Méndez, E. Torres, S. Valea and G. M. García Ríos during field work and Mr. Cormac de Brun for revision of the English. They are indebted to R. Domínguez, M. I. Blanch Matute, and A. Justo for their unselfish involvement in the project. They sincerely thank B. Pratt and two anonymous reviewers for their constructive comments on the manuscript.
5 Author for correspondence (e-mail: cgarciav{at}bio.ucm.es); phone: 0034913945058; fax: 0034913945034
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