Phragmites australis (Common Reed) Invasion in the Rhode River Subestuary of the Chesapeake Bay: Disentangling the Effects of Foliar Nutrients, Genetic Diversity, Patch Size, and Seed Viability

Abstract

The invasion and expansion of the introduced haplotype of Phragmites australis across North America is of growing concern. Previous studies in the Chesapeake Bay region found that Phragmites was more abundant, had higher foliar nitrogen, and produced more viable seeds in brackish wetland subestuaries with more anthropogenic development of the watershed. Here, we focus on a different scale and address issues related to the invasion of Phragmites within a single subestuary, the Rhode River. We evaluated patterns in seed viability, foliar nutrient concentrations, patch size, and genetic variation in ten Phragmites patches in wetlands that occur in the side of the subestuary that is surrounded by forest and 10 patches in wetlands that are in the side of the subestuary that has extensive anthropogenic development. Seed viability varied from 0-60% among the 20 patches but did not differ significantly between patches on the developed vs. forested sides of the Rhode River. Foliar nutrients also did not differ between patches on the two sides of the Rhode River. Seed viability, however, was negatively related to foliar nutrients. Most Phragmites patches consisted of >1 genotype. Larger patches had multiple genotypes, and patches with more genotypes produced more viable seeds. Our study indicates that the Rhode River subestuary behaves as one system with no differences in the measured Phragmites variables between the forested vs. developed sides of the watershed. Our findings also suggest a cyclical process by which Phragmites can spread: larger patches contain more genetic diversity, which increases the chances for cross-fertilization. The subsequent increased production of viable seeds can increase local levels of genetic diversity, which can further facilitate the spread of Phragmites by seed.

Moving from a regional to a continental perspective of Phragmites australis invasion in North America

“…The ability of introduced P. australis patches to spread by seed can vary because: (i) seed viability differs greatly between patches, due to the availability of out-crossed pollen, (ii) P. australis seed densities in seed banks reflect patch-level viable seed production, and (iii) floret and inflorescence production is driven strongly by nutrient levels (Kettenring and Whigham 2009; Baldwin et al 2010; Kettenring et al 2010, 2011). Each of these factors drives variability in reproductive output and potential spread by seed between introduced P. australis patches.…”

Spatial neighborhood effect and scale issues in the calibration and validation of a dynamic model of Phragmites australis distribution – A cellular automata and machine learning approach

“…Kettenring et al (2010) found evidence that larger patches display higher genetic diversity, which in turn increases the production of viable seeds that can establish and expand vegetatively. Additionally, the presence of large reed colonies may cause alteration in the site's conditions favoring Phragmites expansion, a phenomenon known as niche construction (Drake and Kramer, 2011).…”

Evaluating Adaptive Processes for Conservation and Management of Estuarine and Coastal Resources

“…Considering predicted sea level rise and shifts in temperature and salinity (IPCC 2007), estuarine and coastal systems are also an obvious immediate target ecosystem for exploration of how species adapt to the stress associated with global climate change. These stresses include not only the long-established problems of nutrient loading and contamination from urban development (Gedan et al 2009), but also rapidly changing abiotic conditions (Chevin et al 2010;Rohr and Raffel 2010) and competition from invasive species (Freeman and Byers 2006;Richards et al 2008;Kettenring et al 2010). Understanding the evolutionary basis of trait response will be critical for predicting how organisms will respond to the challenges of anthropogenic alteration of the global environment.…”