| Phragmites australis (Cav.) Trin. ex Steudel (Poaceae), the common reed, is a globally distributed plant that has a strong influence in wetland ecosystems. This research addresses some questions about the role of Phragmites in ecosystems and in wetland plant communities and about its population dynamics. The answers to these questions have implications for management strategies.; Wetlands systems generally are considered to act as filters, retaining allochthonous metals that can have toxic effects on biota. We investigated spatial patterns of trace metal concentrations in tissues of Phragmites australis and sediments in the marshes of the Danube Delta, Romania. Sediment metal concentrations decreased significantly with distance from the Delta origin. Sediment and root concentrations of metals were not correlated, suggesting that factors other than labile concentrations in sediments control metal uptake and storage in roots.; Alpha diversities of marshes of six plant community types in the Charles River watershed in Massachusetts, USA, were compared to assess the impact of invasion by Phragmites australis and Lythrum salicaria. The means of jackknifed diversity index values for all types of marsh were statistically significantly different from each other. Typha/Zythrum marshes had the highest values, and Phragmites marshes had the lowest, being monospecific in their central areas. These results suggest that a reduction in diversity can be expected in marshes which are colonized by Phragmites. However, the high level of diversity in the Typha/Lythrum marshes contradicts the expectation of lower diversity after invasion by Lythrum.; Genetic relationships among and within populations of Phragmites australis in the Charles River watershed were investigated using the Random Amplified Polymorphic DNA (RAPD) technique. Cluster analysis generally grouped populations geographically, with distance along the river, and strongly separated the populations on the Charles from those on a tributary, the Muddy River, suggesting a different source of propagules for each of these population groups. Three out of four transects through large stands of Phragmites showed changes with distance, indicating that the genetic structure of the clonal stands is variable. Nested ANOVA results suggest that the populations are very closely related, and that variation in the metapopulation is small. |
