Nutrient uptake into navel oranges during fruit development

Abstract

SummaryChanges in the nutrient content of oranges from young and mature ‘Bellamy’ navel orange trees were measured throughout fruit development. Calculated net influxes of the macronutrients, K, Ca, Mg, P and S, and the micronutrients, Fe, B, Zn, Mn and Cu increased during Stage I of fruit development and reached a maximum 8–10 weeks after flowering (ca. two weeks after the end of Stage I). There was little temporal variation of flux maxima between fruit from young and mature trees, but flux maxima were higher for most nutrients in fruit from mature trees compared with fruit from young trees. During early growth (fruit dry weight <10.g) the contents of K and B (phloem mobile), and of Ca and Cu (phloem immobile) increased linearly in relationship to fruit dry weight. In contrast to K and B, the Ca and Cu content plateaued at a fruit dry weight of 15.g. During Stage I of fruit development the K influx, normalized to fruit dry weight, was the same in fruit from young and mature trees but the normalized Ca flux was higher in fruit from young trees than from mature trees. There was comparatively greater influx of Ca into the albedo than the pulp during Stage I of fruit development. During Stage I of fruit development, normalized Ca fluxes into whole fruit and albedo tissue were higher in fruit from young trees than in fruit from mature trees. The latter have a history of high incidence of rind crease. The results are discussed in relation to the relative mobility of nutrients in phloem and xylem during fruit growth.