Effects of Metal Ions on Growth of and on Ion Absorption by Spirodela polyrhiza (L.) Schleiden Effects of Iron, Magnesium and Zinc

Fronds of Spirodela polyrhiza (L.) Schleiden (duckweed) were grown under axenic conditions. Three series of two-week experiments were performed. In each series the concentration of iron, magnesium or zinc was varied, but all other elements remained in a constant concentration. Thirty-five different concentrations of iron were used, the iron content varying from 0 to 0.72 mol·m^-3. In the case of magnesium and zinc fifty concentrations of each metal were used, the metal content varying from 0 to 4.12 mol·m^-3 for Mg and from 0 to 1.53 mol·m^-3 for Zn. For each culture the frond multiplication rate and the rate of increase in biomass were measured. After two weeks the fronds were analysed for their Fe, Cu, Ca, Zn, Mn and Mg content. Whereas high concentrations of Fe and Zn resulted in decreased frond multiplication rates, high Mg concentrations did not affect this rate. Although the increase in biomass per unit time showed an optimum curve for each of the varied elements, the weight per frond remained quite constant with varying Fe, showed an optimum value for Mg and increased with increased Zn concentration.

The data obtained point to the possible existence of coupled uptake mechanisms for Fe and Cu, Mg and Mn and for Zn and Ca.