FLUXES OF NITROGEN WITHIN DECIDUOUS FRUIT TREES

Abstract. Nitrogen (N) nutrition is a major means of controlling growth and fruiting of trees. In EU Countries, society’s expectations and political decisions have pushed for the adoption of sustainable ways to manage orchards. Guidelines for N management aim to limit fertiliser applications under threshold limits, in order to reduce N losses. Increasing the effectiveness of the recycling of the N present in the orchard is a basic step to reduce external N inputs. The availability of the stable isotope 15N as experimental tool has made possible significant advances in the knowledge of the fluxes of N at tree and orchard level. This paper discusses the N fluxes occurring within the tree both between the years and within the year (root-shoot-root N recycle) and their role in the vegetative and repro-ductive cycle of fruit trees. Key words: Nitrogen storage, nitrogen remobilization, shoot-root-shoot nitrogen recy-cling, xylem sap compositio