PARENT SESSION
Poster Session #37: Plant Ecology: Populations.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC
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Ramet Density effect on sexual and clonal reproduction of Schoenoplectus americanus (i.e. Scirpus olneyi ).
Makihiko, IKEGAMI*,1,2, WHIGHAM, Dennis1,2, WERGER, Marinus1,2, 1 Smithsonian Environmental Research Center (SERC), Edgewater, MD2 Department of Plant Ecology, Utrecht University, Utrecht, The Netherlands
ABSTRACT- We studied the relationships between ramet density and sexual and clonal reproduction of Schoenoplectus americanus (i.e. Scirpus olneyi), an emergent macrophyte in brackish marshes in eastern North America. This species spreads by sexual reproduction and clonal propagation, however, field populations mostly consist of asexual ramets that form dense mono-specific patches. Within dense patches, spreading by clonal growth may not be evolutionarily beneficial because few open spaces are available for new ramets. On the other hand, spreading by seeds may be beneficial, since seeds can disperse to open areas or areas where ramet density is low. From an evolutionary perspective, plants may shift their reproductive strategy from clonal to sexual reproduction as ramet density increases. We tested this hypothesis by sampling S. americanus growing at different densities. We established 16 plots along three 50m transects in each of three salt marshes. At 3m intervals, we counted the number of flowering and non-flowering shoots in 50 ×50cm plots. We excavated below ground rhizomes to measure rhizome length and weight. Rhizomes were placed into two categories based on length. The ratio of flowering shoots to all shoots and the ratio of short-rhizomes to all rhizomes increased as ramet density increased. Results suggest that S. americanus produces seeds and shorter rhizomes at high densities thus increasing the potential for sexual reproduction. At lower densities, vegetative spreading is more important than sexual reproduction.
KEY WORDS: Schoenoplectus or Scirpus , clonal plant, density effect, reproduction