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'S and 2.50%, were toxic to Pistia stratiotes L. and Eichlornia crassipes (Mart.) Solms, respectively. Salinities of 16.65Sc, or higher were toxic to Lemna minor L., but growth of Lemna was increased by salt concentra- tions of 0.83?, 1.66S(, 2.506/c, and 3.33%, as compared to other Lemna plants grown in fertilized pondwater. Other species studied, Hydrilla v'erticillata Royle, Myriophlyllumn spica- tum L., Najas quadalupensis (Spreng.) Magnus, Vallisneria amnericana Michx., Azolla caro- liniana Willd., and Salvinia rotundifolia Willd., gradually declined in growth as salinity in- creased. Transpiration of the emersed growth form of Myriophyllumn brasiliense Camb. decreased with increasing levels of salinity, but root growth was stimulated by salt concen- trations of 0.83(,-3.33%,, presumably a response of the plant to overcome an internal water deficit resulting from the saline solutions.