Significance of fruit transpiration on calcium nutrition in developing apricot fruit

The first objective of this study was to search for a possible correlation between accumulation of calcium (Ca), potassium (K), and magnesium (Mg) and fruit transpiration in developing apricot (Prunus armeniaca L.) fruit. Secondly, the work aimed to determine the significance of transpirational flux on Ca nutrition. We hypothesized that if the fruit transpiration is the determining factor of Ca accumulation (phloem-immobile element) then the import of Ca would be suppressed by restriction of fruit water loss, while the import of phloem-mobile nutrients (i.e., K and Mg) would not be. To test this hypothesis, the seasonal changes of transpiration and of Ca, K, and Mg concentration/ accumulation were assessed in fruits left to naturally transpire or under restricted transpiration (bagged fruits). Fruit transpiration was measured on detached fruits using a portable gas-exchange equipment (ADC-LCA4, ADC BioScientific Ltd, Hoddesdon, England). Results demonstrated that 83% of total fruit Ca content was gained within the first 4 weeks after fruit-set, and that Ca import ceased concomitantly to a reduction of transpiration. In spite of the limitation of fruit transpiration, Ca entered the nontranspiring fruits, and its concentration was about 45% of that in control fruits suggesting that other factor(s) operated for Ca accumulation. This study provides the evidence that fruit transpiration accounted for 55% of total Ca that entered a fruit. We conclude that optimal soil Ca availability and apportioning to the fruit during the early 4 weeks of growth are essential to sustain the fruit demand of this nutrient and that some cultural practices (e.g., summer pruning, irrigation) should be tested as possible tools to improve fruit Ca nutrition via increasing fruit transpiration.