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Annals of Botany 90: 437±443, 2002 doi:10.1093/mcf208, available online at www.aob.oupjournals.org

A Simulation Study on the Importance of Size-related Changes in Leaf Morphology and Physiology for Carbon Gain in an Epiphytic Bromeliad
G E R H A R D ZO T Z 1 , 2 , * , P E T E R R E I C H L I N G 3 and F E R N A N D O V A L L A D A R E S 4 of Botany, University of Basel, Switzerland,2Smithsonian Tropical Research Institute, Balboa, Panama, 3Lehrstuhl fur Botanik II der Universitat Wurzburg, Wurzburg, Germany and 4Centro de Ciencias Medioambientales, È È È È CSIC, Serrano 115, E-28006 Madrid, Spain
1Institute

Received: 15 March 2002 Returned for revision: 3 June 2002 Accepted: 18 June 2002 Published electronically: 4 September 2002

This study addresses the question of howsize-related changes in leaf morphology and physiology in¯uence light absorption and carbon gain of the epiphytic bromeliad Vriesea sanguinolenta. A geometrically based computer model, Y-plant, was used for the three-dimensional reconstruction of entire plants and for calculation of whole plant light interception and carbon gain. Plants of different sizes were reconstructed, and morphological andphysiological attributes of young and old leaves, and small and large plants were combined to examine the individual effects of each factor on light absorption and carbon gain of the plant. The in¯uence of phyllotaxis on light absorption was also explored. Departure of measured divergence angles between successive leaves from the ideal 137´5° slightly decreased light absorption. The only morphologicalparameter that consistently changed with plant size was leaf shape: larger plants produced more slender foliage, which substantially reduced selfshading. Nevertheless, self-shading increased with plant size. While the maximum rate of net CO2 uptake of leaves increased linearly with plant size by a factor of two from the smallest to the largest individual, the potential plant carbon gain (based ontotal foliage area) showed a curvilinear relationship, but with similar numerical variation. We conclude that leaf physiology has a greater impact on plant carbon gain than leaf and plant morphology in this epiphytic bromeliad. ã 2002 Annals of Botany Company
Key words: Crown architecture, ecophysiology, epiphytes, light capture, modelling, photosynthesis, plant size, scaling, Vrieseasanguinolenta.

INTRODUCTION The effective display of leaves in a canopy is crucial for plant functioning because it determines the ef®ciency of the photosynthetic conversion of available light to assimilate and thus in¯uences the potential growth of plants. Ecophysiological studies on plant responses to the light environment have typically focused on individual organs, primarily leaves (Boardman, 1977;Evans et al., 1988; Lambers et al., 1998), while the functional implications of light-induced changes in plant morphology for whole plant performance have received much less attention (Givnish, 1988; Pearcy and Yang, 1996; Valladares and Pearcy, 1998). Strong selection pressure is presumed to reduce mutual shading among leaves of the same plant and this presumption has motivated a number of studieson crown architecture and adaptations that may reduce self-shading (Niklas, 1988, 1992; Yamada et al., 2000; Valladares et al., 2002). To minimize self-shading during growth, plants may change leaf orientation, petiole length and angle, and leaf deployment and turnover (Pearcy and Yang, 1998; Yamada et al., 2000). However, no architectural solution prevents self-shading completely, especially whenleaf area increases as a result of plant growth.
È * For correspondence. Botanisches Institut der Universitat Basel, È Schonbeinstrasse 6, CH-4056 Basel, Switzerland. Fax +41 (0) 61 267 35 04, e-mail Gerhard.zotz@unibas.ch

Architectural changes during growth, which may also be related to other limitations such as mechanical stresses or the translocation of water and nutrients (Niklas and...