Encrustations and element composition of charophytes from fresh or brackish water sites - habitat- or species-specific differences?

Comparison of encrustation and analysis of element contents across species growing in freshwater (FW) and brackish water (BW) have never been done. Proportion of carbonate and element composition for Ca, K, Mg, Na, and P of plant DW were investigated in four charophyte species from ten freshwater and six brackish water sites in northern Europe. Chara aspera and C. tomentosa were found in both FW and BW sites, whereas C. subspinosa and Nitellopsis obtusa occurred in freshwater only. Significant differences in encrustation were found between FW and BW sites. Individuals from FW had a far higher carbonate content based on dry weight than individuals from BW. In BW, C. tomentosa was less encrusted than C. aspera. This might be explained by the osmoregulation capacities of the brackish water species. The K/Na ratio differed between FW and BW in a species-specific manner. Element composition was habitat-specific for Ca and Mg, species-specific for K, and habitat- and species-specific for Na. P contents showed no specific pattern.