Kettenring, Karin , Mccormick, Melissa , Whigham, Dennis .
A feedback mechanism for the spread of the invasive plant Phragmites australis – increased local genetic diversity and cross pollination can drive viable seed production.
Phragmites australis is rapidly invading wetlands across North America but little is known about how this plant spreads and what can explain its often exponential expansion. We have documented high levels of genetic diversity within and among Phragmites patches in subestuaries of the Chesapeake Bay, indicating the importance of sexual spread. We also found highly variable seed viability, but that seed viability was highest in wetlands with developed watersheds, where plants are known to have higher foliar nitrogen levels, than those in forested watersheds. We hypothesized that nutrient availability may be important in Phragmites viable seed production. However, because of the high variation in seed viability, other factors such as cross pollination may be important. Here we report the results of a common garden study where we evaluated the importance of nutrients and cross-pollination on viable seed production. Over 2 years we grew plants from genetically distinct populations from 4 subestuaries of the Chesapeake Bay. Plants were subjected to elevated or ambient nitrogen and phosphorous levels. In year 2 flowering commenced and plants were either self- or cross-pollinated. We dissected seeds from each inflorescence to determine percent seed viability. We found a weak negative effect of elevated nutrients on seed viability; however these same plants also produced more inflorescences per plant so the net effect is higher viable seed production per plant. We also found a strong positive influence of cross-pollination on seed viability; cross-pollinated plants produced 10x as many seeds. We suggest that this positive effect of cross-pollination on viable seed production provides a mechanism to explain the often exponential increase of Phragmites in the Chesapeake Bay. As local levels of genetic diversity accumulate with individuals establishing via seed, the potential for cross-pollination and viable seed production can increase, causing a feedback mechanism for rapid spread by seed.
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1 - Utah State University, Ecology Center and Department of Watershed Sciences, 5210 Old Main Hill, Logan, UT, 84322, USA
2 - Smithsonian Environmental Research Center, P.O. Box 28, 647 Contees Wharf Rd., Edgewater, MD, 21037, USA
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Wasatch B/Cliff Lodge - Level C
Date: Monday, July 27th, 2009
Time: 8:30 AM