Autumnal nitrogen nutrition affects the C and N storage and architecture of young peach trees
Résumé
Nitrogen fertilisation is a regular practice in orchards. Its effect on tree development, N and C acquisition and allocation were evaluated simultaneously, while coupling on the same trees in situ measurements of N uptake and shoot development and destructive determinations
of organ composition in N and Total Non structural Carbohydrates (TNC). An hydroponic set-up was designed that could grow young peach trees at constant NO3 concentration while measuring N uptake. Forty-eight trees were raised outdoors under excessive N supply. Between October 2 and December 7, half of them were then N-limited to reduce N uptake by 75%. Organ N concentrations remained stable in the controls but were halved in
N-limited trees. Growth (390 vs. 353 g DW tree-1) was less affected by the treatment than N uptake (10.6 vs. 2.7 g N tree-1). Growth was affected only in terms of axillary bud development, which was restricted to the median and upper crown parts. The number of buds which transformed into elongating axes (44 vs. 84 tree-1) was halved, thus reducing leaf area by one-third (10,464 vs. 15,568 cm2). Tree TNC content was not impacted. The difference in C acquisition likely balanced the C costs of N uptake. In N-limited trees, more TNC was stored as starch (73 vs. 56%), and the allocation patterns of TNC and N were altered in favour of the roots. Our results provide deeper insights into the tree integrated response to
autumnal N fertilisation, focusing on an alteration of the balance between storage and growth.