Influence of salinity on the absorption of rubidium by Spartina alterniflora and Distichlis spicata

The effects of NaCl, CaCl2, and MgCl2on the absorption of Rb by excised roots and intact seedlings of Spartina alterniflora, and of NaCl on Rb absorption by Distichlis spicata, were studied. In both species, the rate of Rb absorption was reduced when the concentration of NaCl in the external solution was equal to or exceeded 10 mM NaCl. The reduction was proportional to the concentration of NaCl. In S. alterniflora the Ca concentration for maximum Rb absorption by excised roots was 2 mM, about 4 times that reported for nonhalophytes. Magnesium at concentrations up to 40 mM was a poor substitute for Ca, as the Mg-mediated Rb absorption was 2-3 times slower than Ca-mediated absorption.