Incomplete turgor adjustment in Cladophora rupestrisunder fluctuating salinity regimes

Abstract

Turgor pressure fluctuates strongly in Cladophora rupestris subjected to low salinities and shows only a small tendency to readjust to the normal value in full seawater (incomplete turgor adjustment). This was revealed by direct turgor pressure measurements and by chemical analyses of osmotic solutes after exposure of upper and lower shore Cladophora to the different salinity regimes occurring in the intertidal zone or representing steady state osmotic acclimation. The main internal osmotic solutes were K + , Cl − , amino acids, NO 3 − and glycine betaine. Na + , SO 4 2− and PO 4 3− were of less importance. The sum of the charges on the cations was similar to that for the anions. K + , Cl − and, to a lesser extent, amino acids were responsible for limited turgor pressure adjustment which did occur. The concentrations of the major osmotic solutes were influenced not only by salinity but also by light: those of amino acids and NO 3 − were increased while those of K + and Cl − were decreased under illumination. Cladophora populations from the upper and lower shore differed in their ability to restore internal K + and Cl − levels on transfer to full seawater after long term exposure to low salinity. This may indicate ecotypic variation.