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

Abstract

Tomato fruit grown in diurnally fluctuating salinities (8 mS cm−1 during the day and 3 mS cm−1 at night; 8/3 mS cm−1), accumulated the same amount of dry matter and magnesium (Mg) as those in constant 3 or 8 mS cm−1, but an intermediate amount of calcium (Ca). Raising the salinity of the nutrient solution by enriching with macronutrients or by adding NaCl had similar effects. The uptake of 45Ca by tomato plants during the day was greater than at night and was reduced by salinity in both periods. While the uptake of 45Ca by 8/3 mS plants at night was similar to that of 3 mS plants, the daily uptake was less than that in 3 and 5.5 mS plants. The Ca content of tomato fruit increased with truss number at 3 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 content but higher Mg content than the proximal fruit. The reduction in Ca content of the distal fruit at 8/3 mS cm−1 was similar to that at 5.5 mS cm−1. The Ca content of the tissue at the distal end of the 8/3 mS fruit was lower than that of the 5.5 mS fruit. Similarly, the distribution of 45Ca to the distal half of the detached 8/3 mS fruit was less than that of 5.5 mS fruit. A reduced uptake and inadequate distribution of Ca to the truss and to the distal end of the 8/3 mS fruit were the main causes of these differences.