We compared the ecophysiological performance of four dominant, perennial plant species of tidal marshes of northeastern North America (Phragmites australis, Typha angustifolia, Spartina alterniflora, and Leersia oryzoides), asking whether species that fall along a continuum of invasiveness vary consistently in terms of primary productivity, growth, biomass allocation, phenology, maximal photosynthetic rate, leaf turnover, tissue nutrient and chlorophyll content, and water use. During 1999, we examined plants growing at two brackish marshes and two freshwater tidal marshes in southern Connecticut, USA. Phragmites and Typha consistently exceeded the other two species in both marsh types in terms of ramet biomass, standing crop, length of the growing season, standing leaf area, leaf longevity, and total chlorophyll. Typha, Phragmites, and Spartina showed similar maximal photosynthetic rates across marsh types, significantly greater than the Pmax observed in Leersia. Foliar nitrogen was significantly greater in Phragmites than in all other species, suggesting that this species accrues nutrients more efficiently. Phragmites and Typha populations did not differ in a number of characters between freshwater and brackish marshes, indicating low sensitivity to exposure to moderate salinity levels. A principle components analysis placed Phragmites and Typha close to each other and more distant from Spartina and Leersia along axes describing components of competitive ability and photosynthetic performance. Thus, moderately and highly invasive species are distinct from less invasive species in terms of ecophysiology in both wetland types. As Phragmites australis and Typha angustifolia displace other plant species in marshes, they will likely influence the carbon- and nitrogen-cycling functions of wetlands, subject to the species' varying tolerances for salinity.
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Vol. 23 • No. 4