Difference in -response of rice and tomato subjected to sodium salinization to the addition of calcium

Rice (Oryza sativa L. cv. Yamabiko) and tomato (Lycopersicon esculentum Mill cv. Saturn) plants were subjected to Na-salinization (80 mmol( + ) kg^-1) in hydroponics. The effect of the addition of Ca on their growth was analyzed in terms of transpiration, ion uptake, and ion transporto.

The addition of 10 mmol( + ) kg^-1 Ca improved rice growth by decreasing the Na uptake and increasing the K and Ca uptake. It was worth noting that the Na uptake accompanied with water uptake (transpiration) was not affected by the addition of Ca. A close relationship was found in rice among the osmotic potential, cumulative transpiration, and top dry weight; The growth of rice, therefore, seemed to depend on the osmotic potential of the solution.

The growth suppression of the tops and roots brought about by Na and recovery by the addition of Ca were greater for tomato. Ca improved tomato growth by reducing the Na uptake and increasing the uptake of K and Ca, as was observed in rice. The selectivity of plants for potassium versus sodium (S_K,Na) increased sharply with the increase of the Ca concentration. Moreover, the transport of Na to the tops was suppressed by the addition of Ca. It was found that the osmotic potential, transpiration, and dry matter yield were not correlated with each other. It was concluded from the results that the growth recovery of tomato plants subjected to Na-salinization by the addition of Ca may be associated with the suppression of Na transport to the tops rather than with the antagonism between Ca and Na at the root surface.