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(American Journal of Botany. 2009;96:612-619.) doi: 10.3732/ajb.0800166 © 2009 Botanical Society of America, Inc.

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Should structure–function relations be considered separately for homobaric vs. heterobaric leaves?¹

² Laboratory of Plant Physiology, Department of Agricultural Biotechnology, Agricultural University of Athens, Iera Odos 75, 118 55, Athens, Greece ³ Chair of Tree Physiology, Albert Ludwig University of Freiburg, Georges-Köhler-Allee, Gebäude 053/054, 79110 Freiburg i. Br., Germany

ABSTRACT

Tree and shrub species can be differentiated into two major groups based on their substantially different leaf anatomy: heterobaric and homobaric. In contrast to homobaric leaves, heterobaric leaves have bundle sheath extensions (BSEs) that create transparent regions on their lamina. Recent studies have shown that BSEs transfer visible light to internal mesophyll layers, thus affecting the photosynthetic performance of heterobaric leaves. Whether the two leaf types also differ in other functional and structural traits has not been addressed, nor have any structure–function relations. Here, we measured key anatomical and physiological parameters and tested their relationships in 30 species with different leaf types. Heterobaric leaves were thinner with lower leaf mass per area, had higher nitrogen concentration per mass, were ¹³C-enriched, and achieved comparable photosynthetic capacity per area but had higher photosynthetic capacity per mass compared to homobaric leaves. Relations between leaf construction cost, nitrogen concentration, and photosynthesis followed the general pattern of the "leaf economic spectrum," but differed between homobaric and heterobaric leaves. We suggest that the mechanisms controlling these relations differ between the two leaf types, presumably due to their distinct anatomy.

Key Words: bundle sheath extensions • heterobaric leaves • homobaric leaves • leaf anatomy • nitrogen concentration • photosynthetic capacity • ¹³C

Received for publication 12 May 2008. Accepted for publication 21 October 2008.

FOOTNOTES

¹ The authors thank Dr. T. Konstantinidis for help with plant species identification and Dr. G. Liakopoulos for assistance with TLA calculations. Dr. T. Awada, University of Nebraska, is also acknowledged for helpful criticism of the manuscript. V.L. thanks the Foundation for National Scholarships, Greece, for financial support during postdoctoral studies.

⁴ Author for correspondence (e-mail: karab{at}aua.gr), phone/fax: +30 210 5294286

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