title: Dynamics of nitrogen uptake and mobilization in field-grown winter oilseed rape (Brassica napus) from stem extension to harvest: I. Global N flows between vegetative and reproductive tissues in relation to leaf fall and their residual N.
abstract: OBJECTIVE
  Despite its high capacity to take up nitrate from the soil, winter oilseed rape (Brassica napus) is characterized by a very low N recovery in the reproductive tissues under field conditions. A significant part of the N taken up is lost to the soil in dead leaves during the growth cycle. An accurate description of N dynamics at the whole plant level in each compartment under field conditions should lead to a better understanding of N allocation in B. napus and improvements in the nitrogen harvest index.
  
  
  METHODS
  An experiment was conducted in field conditions using sequential weekly 15N labelling to follow N uptake, partitioning and mobilization. Nitrogen labelling (2.5 kg N ha(-1); 10 % excess) was analysed weekly (from stem extension to harvest) to distinguish between uptake of new N (labelled) and mobilized N (unlabelled) in the different plant components.
  
  
  CONCLUSIONS
  N requirements for seed filling were satisfied mainly by N mobilized from vegetative parts (about 73 % of the total N in pods). Determination of the endogenous N flow showed that there was net transfer of N to the pods by leaves (36 %), stem (34 %), inflorescences (22 %) and taproot (8 %). Precise study of N flow from leaves at different nodes revealed the existence of two main groups of leaves in terms of their apparent capacity to mobilize N; 30-60 % and 70-80 % of peak N content occurring during flowering and pod filling, respectively. Moreover, the latter group was found to be the main source of endogenous N from leaves. The mobilization of endogenous N from these leaves was prolonged and concomitant with N accumulation in the pods. A complex pattern of N mobilization from the leaves, to vegetative or reproductive tissues, was revealed. These results will be used to model N partitioning during the growth cycle.
authors.affiliation: 1-UMR INRA-UCBN 950 EVA, Ecophysiologie Végétale, Agronomie et nutritions N, C, S, Institut de Biologie Fondamentale et Appliquée, Université de Caen Basse Normandie, F-14032 Caen Cedex, France.
authors.forename: P
authors.initials: P
authors.lastname: Malagoli
authors.forename: P
authors.initials: P
authors.lastname: Laine
authors.forename: L
authors.initials: L
authors.lastname: Rossato
authors.forename: A
authors.initials: A
authors.lastname: Ourry
mesh_terms: D001692:Biological Transport; D018533:Biomass; D029688:Brassica napus / Q000378:metabolism*; D007553:Isotope Labeling; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D018547:Plant Stems / Q000254:growth & development / Q000378:metabolism*; D013696:Temperature
chemical_list: D009584:Nitrogen