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First published online March 20, 2009; doi:10.3732/ajb.0800149 American Journal of Botany 96: 786-792 (2009) © 2009 Botanical Society of America, Inc.

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Inflorescences contribute more than rosettes to lifetime carbon gain in Arabidopsis thaliana (Brassicaceae)¹

Department of Biological Sciences, University of Pittsburgh, 162B Crawford Hall, 4249 Fifth Avenue, Pittsburgh, Pennsylvania 15260

ABSTRACT

A metamorphosis from rosette to inflorescence in many annuals shifts photosynthetic tissue from a two-dimensional array in the soil boundary layer during cool months to a three-dimensional structure in the troposphere as spring progresses. We propose that this shift allows escape from both self-shading and an increasingly stressful boundary layer microclimate, permitting continued increases in growth. As a first step in exploring this hypothesis, we compared the lifetime C gain, water loss, and instantaneous water use efficiency (WUE) of five Arabidopsis thaliana genotypes by measuring gas exchange across the life cycle. On average, the inflorescence contributed 55% (± 5% SE) of lifetime C gain, but only 25% of lifetime water loss. Mean inflorescence WUE was nearly fourfold that of the rosette. The inflorescence continued to fix C after rosette senescence. The percentage inflorescence: total C gain varied among genotypes, from 36% to 93%. Genotypes differed in WUE for both structures. We suggest that local climates may have selected for divergence in these traits. For many annuals and winter annuals, understanding C and water budgets and their evolution must include measures of both rosette and inflorescence gas exchange.

Key Words: Arabidopsis thaliana • carbon gain • inflorescence • infrared gas analysis • IRGA • ontogenetic switch • water use efficiency • whole-plant cuvette

Received for publication 28 April 2008. Accepted for publication 23 December 2008.

FOOTNOTES

¹ This was an undergraduate independent research project for E. Early, J. Winkler, and B. Ingland. A. Boulé, P. Brautigam, and K. Pruss provided crucial technical support. The authors are grateful to the PEeR discussion group at the University of Pittsburgh and two anonymous reviewers for invaluable criticism and advice. S. Kalisz was hugely helpful with editing suggestions. National Science Foundation grant DEB-0130347 to S.J.T. provided funding.

³ Author for correspondence (e-mail: tonsor{at}pitt.edu)

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