Effects of Diurnal Changes in the Salinity of the Nutrient Solution on the Accumulation of Calcium by Tomato Fruit

Tomato fruit grown in diurnally fluctuating salinities (8 mScm^–1 during the day and 3 mS cm^–1 at night; 8/3mS cm^–1), accumulated the same amount of dry matter andmagnesium (Mg) as those in constant 3 or 8 mS cm^–1, butan intermediate amount of calcium (Ca). Raising the salinityof the nutrient solution by enriching with macronutrients orby adding NaCl had similar effects. The uptake of ⁴⁵Ca by tomato plants during the day was greaterthan at night and was reduced by salinity in both periods. Whilethe uptake of ⁴⁵Ca by 8/3 mS plants at night was similar tothat of 3 mS plants, the daily uptake was less than that in3 and 5.5 mS plants. The Ca content of tomato fruit increased with truss number at3 and 5.5 mS cm^–1 but not at 8/3 and 8 mS cm^–1.Within the same truss, the distal fruit had a lower Ca contentbut higher Mg content than the proximal fruit. The reductionin Ca content of the distal fruit at 8/3 mS cm^–1 was similarto that at 5.5 mS cm^–1. The Ca content of the tissue atthe distal end of the 8/3 mS fruit was lower than that of the5.5 mS fruit. Similarly, the distribution of ⁴⁵Ca to the distalhalf of the detached 8/3 mS fruit was less than that of 5.5mS fruit. A reduced uptake and inadequate distribution of Cato the truss and to the distal end of the 8/3 mS fruit werethe main causes of these differences. Lycopersicon esculentum(Mill.), tomato, fruit, calcium, magnesium, diurnal salinity