Modeling fruit acidity in peach trees effects of nitrogen and potassium nutrition

Mineral nutrition affects several components of fruit quality in rosacea species. Among them, fruit acidity clearly depends on potassium and nitrogen nutrition, bit the mechanisms involved are complex. Potassium stimulates the accumulation in fruits of organic acids and partly neutralises their acidity. Nitrogen nutrition may affect fruit acidity, but it interferes with potassium uptake by roots and allocation to fruits, fruit growth and maturation, so that the observed effects in field experiments are often contradictory. In order to understand these interactions in peach trees, a model that integrates the effects of fruit growth and mineral accumulation in the fruit has been built to simulate the synthesis of organic acids in the cytoplasm, and their storage in the vacuole. Fruit growth, potassium and sugar contents are the main entries of the model, while fruit pH and titrable acidity are the main outputs. When the effects of nutrogen and potassium nutrition on fruit growth and composition are known (by measurements or an independent nutrition model), the acidity model allows to simulate the synthesis of organic acids, the ionic interactions that affect their storage in the vacuole, and finally the pH and titrable acidity of the fruit. Such effects are presented, and their consequences for the management of mineral nutrition ti improve fruit quality are discussed.