Effects of Salinity on Growth of Several Aquatic Macrophytes

Growth rates of 10 aquatic macrophytes in various salinities under greenhouse conditions varied widely. Salt concentrations of 1.66% and 2.5% were toxic to Pistia stratiotes L. and Eichornia crassipes (Mart.) Solms, respectively. Salinities of 16.65% or higher were toxic to Lemna minor L., but growth of Lemna was increased by salt concentrations of 0.83%, 1.66%, 2.50%, and 3.33% as compared to other Lemna plants grown in fertilized pondwater. Other species studied, Hydrilla verticillata Royle, Myriophyllum spicatum L., Najas quadalupensis (Spreng.) Magnus, Vallisneria americana Michx., Azolla caroliniana Willd., and Salvinia rotundifolia Willd., gradually declined in growth as salinity increased. Transpiration of the emersed growth form of Myriophyllum brasiliense Camb. decreased with increasing levels of salinity, but root growth was stimulated by salt concentrations of 0.83%—3.33%, presumably a response of the plant to overcome an internal water deficit resulting from the saline solutions.