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(American Journal of Botany. 2008;95:1366-1374.) doi: 10.3732/ajb.0800019 © 2008 Botanical Society of America, Inc.

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Do bryophyte shoot systems function like vascular plant leaves or canopies? Functional trait relationships in Sphagnum mosses (Sphagnaceae)¹

³ Department of Biological Sciences, Union College, Schenectady, New York 12308 USA ⁴ Department of Biology, University of New Mexico, Albuquerque, New Mexico 87131 USA

ABSTRACT

Vascular plant leaf traits that influence photosynthetic function form the basis of mechanistic models of carbon exchange. Given their unique tissue organization, bryophytes may not express similar patterns. We investigated relationships among tissue, shoot, and canopy traits, and their associations with photosynthetic characteristics in 10 Sphagnum species. Trait relationships were organized around a primary dimension accounting for 43% of variation in 12 traits. There was no significant relationship between nitrogen content of shoot systems and maximum photosynthesis expressed on mass (A_mass) or area (A_area) bases due to nitrogen sequestration and storage within the canopy interior. This pattern differs from the distribution of nitrogen in vascular plant canopies. Thus, nitrogen and its relationship to carbon uptake in Sphagnum shoots does not conform to patterns of either vascular plant leaves or canopies. Species that concentrate biomass and nitrogen in the capitulum have enhanced rates of A_mass and A_area. Consequently, A_area was positively associated with N_area of the capitulum only. Overall, water content and carotenoid concentration were the strongest predictors of both A_mass and A_area and these were expressed as inverse relationships. The relationships of plant traits in Sphagnum defines a principal trade-off between species that tolerate environmental stress and those that maximize carbon assimilation.

Key Words: bryophyte • carbon isotope fractionation • carotenoid • nitrogen concentration • peatmoss • photoinhibition • plant functional type

Received for publication 16 January 2008. Accepted for publication 11 September 2008.

FOOTNOTES

¹ The authors thank B. Shaw, J. Shaw, R. Andrus, L. Smith, G. Smith, and T. Fitzgerald for assistance identifying collecting localities or for access to collection sites. L. Giles, L. Fleishman, and J. Kelbeck provided help with laboratory equipment or analyses. The manuscript was improved by comments from three anonymous reviewers. Financial support was received from Union College’s Internal Education Foundation and Faculty Research Fund Grants and from the University of New Mexico.

² Author for correspondence (e-mail: rices{at}union.edu)

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