Separating multiple, short-term, deleterious effects of saline solutions on the growth of cowpea seedlings

• Reductions in plant growth as a result of salinity are of global importance in natural and agricultural landscapes. • Short-term (48-h) solution culture experiments studied 404 treatments with seedlings of cowpea (Vigna unguiculata cv Caloona) to examine the multiple deleterious effects of calcium (Ca), magnesium (Mg), sodium (Na) or potassium (K). • Growth was poorly related to the ion activities in the bulk solution, but was closely related to the calculated activities at the outer surface of the plasma membrane, {Iz}₀ o. The addition of Mg, Na or K may induce Ca deficiency in roots by driving {Ca²⁺}₀ o to < 1.6 mM. Shoots were more sensitive than roots to osmolarity. Specific ion toxicities reduced root elongation in the order Ca²⁺ > Mg²⁺ > Na⁺ > K⁺. The addition of K and, to a lesser extent, Ca alleviated the toxic effects of Na. Thus, Ca is essential but may also be intoxicating or ameliorative. • The data demonstrate that the short-term growth of cowpea seedlings in saline solutions may be limited by Ca deficiency, osmotic effects and specific ion toxicities, and K and Ca alleviate Na toxicity. A multiple regression model related root growth to osmolarity and {Iz}₀ o (R² = 0.924), allowing the quantification of their effects.