Watkins, Jr., James E. , Churchill, Amber , Holbrook, Noel .
A Site for Sori: Consequences for Fertile/Sterile Leaf Dimorphism in Ferns.
Plants allocate resources to maximize fitness, yet reproduction can result in physiological costs. Contrary to seed plants, which often partition fertile structures into costly flowers or fruits, ferns produce fertile structures on the lamina, or leaf surface. The leaf functions in both carbon fixation and reproduction and this may produce trade-offs between maximizing carbon gain and increasing fitness. Due to the pressures on leaf for maximizing fitness, fern species have evolved varying levels of fertile/sterile leaf dimorphism: from complete to monomorphic. To determine ecophysiological consequences of fertile/sterile leaf dimorphism three species were examined: the dimorphic sensitive fern Onoclea sensibilis, the hemidimorphic Christmas fern Polystichum acrostichoides and monomorphic marginal woodfern Dryopteris marginalis. We compared light response curves, water potential and aspects of hydraulic conductivity between fertile and sterile fronds. These data were combined with morphological measurements to understand how fertile and sterile leaves differ. Along our gradient of dimorphism we found that as the level of dimorphism increased the percent of fertile fronds produced decreased. A similar observation was made for fertile frond length which decreased with increasing dimorphism. We also found that there was no difference in xylem vulnerability between fertile and sterile fronds; however, the most dimorphic species exhibited the highest mid-day water potential and the monomorphic species the lowest. In fertile fronds, maximum photosynthetic rates decreased and respiration rates increased with a greater dimorphism. These results reveal that there are important tradeoffs to complete leaf dimorphism at both physiological and morphological levels. While dimorphic species have similarly safe fertile and sterile xylem, fertile fronds maintain water potentials below that, which would result in significant cavitation. Dimorphic species produce well protected, yet fewer, fertile fronds with high respiratory cost that may influence species success. The costs of such structures may account for the rarity of complete dimorphism in ferns.
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1 - Colgate University, Biological Sciences, 13 Oak Drive, Hamilton, New York, 13346, USA
2 - StoneHill College, Biology, 320 Washington St., Easton, MA, 02357, USA
3 - Harvard University, Department of Organismic and Evolutionary Biology, 16 Divinity Ave, Cambridge, MA, 02138, USA
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 28th, 2008
Time: 2:15 PM