Water relations, calcium and potassium concentration in fruits and leaves during annual growth in mature kiwifruit plants

Actinidia deliciosa fruiting plants trained to “Pergola” system were grown in a semiarid environment located in South Italy (Andriace N 40° 20’, E 16° 48’). During the growing season measurements were carried out on leaf area, fruit growth, leaf and fruit transpiration, Ca and K content. In the first period of fruit development the kinetics of calcium uptake was faster than potassium. In particular, 60 days after fruit set, the calcium content reached about 70% of the amount measured at harvest, whereas potassium only reached 50%. This high value of fruit calcium uptake was correlated with high fruit transpiration observed 60 days after fruit set. After this period the fruit transpiration declined due to epidermis structural changes. Fruit calcium concentration and Ca/K ratio decreased during fruit growth, while they constantly increased in leaves. This behaviour confirms that calcium movement between leaf and fruit through the phloem is limited.