How Sodium Chloride Concentration in the Nutrient Solution Influences the Mineral Composition of Tomato Leaves and Fruits

Tomato plants (Solanum lycopersicum L. cv. Durinta) were grown in an open soilless system to evaluate the effects of sodium chloride (NaCl) concentration in the nutrient solution on the ion compositions in plant tissues. The treatments were defined by a factorial combination of five NaCl concentrations and three leaves position/age and two fruits' position. Seedlings were transplanted in perlite and, 7 days after transplanting, five salinity treatments were imposed by adding 7, 21, 37, 49, or 64 mM of NaCl to the nutrient solutions; the final electrical conductivities were: 2.7,4.5, 6.0, 7.5, and 8.6 dS.m(-1), respectively. Increased salinity in the nutrient solution resulted in a reduction in tomato dry matter (from 534 to 375 g per plant) and in a linear increase in sodium (from 0.37% to 1.39%) and chloride (from 1.75% to 5.73%) in the leaves as well as in the fruit tissues (from 0.08% to 0.26% for sodium and from 0.63% to 1.34% for chloride). Leaf under the first cluster showed higher levels of sodium (+54%) and chloride (+32%) than leaf under the fifth cluster and old leaf accumulated more sodium (+15%) and chloride (+25%) than younger ones. The exposure of the tomato plants to increasing salinity resulted in a linear decline in nitrate (from 1.21%) to 0.50%), total nitrogen (from 3.31% to 3.03%), sulphate (from 3.71% to 3.12%), and potassium leaves (from 2.76% to 1.51%); the potassium reduction was more evident in younger leaves than in older ones. All macronutrients, except calcium, decreased in the fruit tissues with increasing NaCl concentration in the nutrient solution. However, for phosphate, the reduction of the ion concentration was evident only in the fruit from the fifth cluster (-35%). The position of the fruit on the plant significantly affected the concentration of ion, which was higher for all determined ions in the fruit of the first truss. The levels of Na+ and Cl- found in the plant tissue seem to confirm the hypothesis that the plant dry biomass reduction may also be traced to the toxicity of these ions as a consequence of this high concentration. On the other hand, although generally influenced by antagonism with sodium and chloride, the amount of main macronutrients did not reach deficiency levels that influenced the growth processes, except in the case of potassium.