ABSTRACT
The productivity of many plants is limited by nitrogen availability, which is particularly true in wood or fruit production by ligneous species. A study on nitrogen management by trees is justified because trees show two characteristics which distinguish them from cultivated herbaceous species: 1) their perennial character involves seasonal management of nitrogen. The reserves, especially of nitrogen, accumulate in the vegetative organs to ensure nitrogen supply when renewed growth begins in spring. 2) Ligneous forest species are often cultivated with limited but constant store of nitrogen involving mechanisms that permit efficient recycling of this element during the development cycle. Trees have thus become the object of special study to quantify the internal flux of nitrogen during vegetative growth. The nitrogen cycle in deciduous trees has been described in detail mainly because 15N was used as a tracer in the nitrogen source used to feed the tree species in experiments wherein the protein reserve in vegetative organs was identified. Lastly, modelling growth enables demonstration of nitrogen management, which must be considered concomitant with the general processes controlling growth, such as photosynthesis and distribution of biomass between plant shoot and root systems.
