Trophic response curves of aquatic bryophytes in lowland calcareous streams

Logistic regression was used to model the response curves of seven aquatic bryophyte species from calcareous lowland streams of two hydrographic netwo rks. Almost all the species exhibited log-normal response curves and signif icant optima when the data coming from the two hydrographic networks were s imultaneously considered but, monotonic response curves,es within each of t he hydrographic networks. The response curves of Amblystegium riparium in t he Walloon hydrographic network, in the Alsatian hydrographic network, and in both networks considered simultaneously, showed a strong overlap. Conver sely, Amblystegium fluviatile showed distinctly different response curves b etween the studied hydrographic networks. This was also the case for A. ten ax, Fissidens crassipes, and Fontinalis antipyretica. Amblystegium tenax ha s a typical oligotrophic status in the Alsatian floodplain, but in the Wall oon hydrographic network, is still present in the most polluted waters whos e annual mean concentrations of N-NH4* can reach up to 9,000 mu g l(-1). Am blystegium fluviatile and Fontinalis antipyretica presented similar respons e patterns, exhibiting optima in eutrophic waters when the data from the tw o hydrographic networks were simultaneously considered, but reaching maxima l occurrence in the most oligotrophic waters in the Walloon hydrographic ne twork. It is suggested that these species might include several ecotypes wi th different trophic requirements.