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First published online September 17, 2009; doi:10.3732/ajb.0800327 American Journal of Botany 96: 1808-1813 (2009) © 2009 Botanical Society of America, Inc.

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Variation in flowering size and age of a facultative biennial, Aster kantoensis (Compositae), in response to nutrient availability¹

² Department of Biological Sciences, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-Osawa 1-1, Hachioji, Tokyo, 192-0397, Japan ³ Institute for Environmental Sciences, 1-7, Rokkasho, Aomori, 039-3212, Japan

ABSTRACT

Although the flowering of facultative biennials is size-dependent, flowering size varies markedly within a single population as well as among populations. In this study, 15 half-sib families of the facultative biennial Aster kantoensis were grown from seeds at three nutrient levels (low, medium, and high). A significant nutrient x family interaction effect was found for bolting size, and among-family variation in bolting size increased with decreasing nutrient level. Growth from bolting to flowering tended to be greatest at the high nutrient level. Such responses of bolting size and growth from bolting to flowering resulted in an increase in flowering size at the high nutrient level and a significant variation in its reaction norm among families. For flowering age, there was a significant interaction of nutrient x family, and its among-family variation increased with decreasing nutrient levels, as was the case with bolting size. These results indicate that genetic variation in phenotypic plasticity of bolting size with nutrient availability was one cause of the variation in flowering size and age in the A. kantoensis population on the floodplain with the spatially heterogeneous nutrient availability. Moreover, responses of growth from bolting to flowering to nutrient availability could enhance the variation in flowering size.

Key Words: Aster kantoensis • Compositae • life history variation • phenotypic plasticity • short monocarpic perennial • threshold size for flowering

Received for publication 25 September 2008. Accepted for publication 19 May 2009.

FOOTNOTES

¹ The authors thank S. Nishitani, J. Suzuki, and H. Kudoh for helpful comments on an earlier version of the manuscript and M. Méndez and an anonymous reviewer for careful reading and comments that improved the manuscript. They are grateful to E. Sugiyama and T. Yasuki for management of the greenhouse at Tokyo Metropolitan University.

⁴ Author for correspondence (e-mail: kachi-naoki{at}ed.tmu.ac.jp)

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