Interactions between Ca, Mg, Na and K: alleviation of toxicity in saline solutions

Abstract

Background and aims

Saline soils limit plant production worldwide through osmotic stress, specific-ion toxicities, and nutritional imbalances.

Methods

The ability of Ca²⁺ and K⁺ to alleviate toxicities of Na⁺ and Mg²⁺ was examined using 89 treatments in short-term (48 h) solution culture studies for cowpea (Vigna unguiculata (L.) Walp.) roots. Root elongation was related to ionic activities at the outer surface of the root plasma membrane.

Results

The addition of K⁺ was found to alleviate the toxic effects of Na⁺, and supplemental Ca²⁺ improved growth further in these partially-alleviated solutions where K⁺ was present. Therefore, Na⁺ appears to interfere with K⁺ metabolism, and Ca²⁺ reduces this interference. Interestingly, the ability of Ca²⁺ to improve K-alleviation of Na⁺ toxicity is non-specific, with Mg²⁺ having a similar effect. In contrast, the addition of Ca²⁺ to Na-toxic solutions in the absence of K⁺ did not improve growth, suggesting that Ca²⁺ does not directly reduce Na⁺ toxicity in these short-term studies (for example, by reducing Na⁺ uptake) when supplied at non-deficient levels. Finally, K⁺ did not alleviate Mg²⁺ toxicity, suggesting that Mg²⁺ is toxic by a different mechanism to Na⁺.

Conclusions

Examination of how the toxic effects of salinity are alleviated provides clues as to the underlying mechanisms by which growth is reduced.