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.
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.
Malagoli
P
P
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.
Laine
P
P
Rossato
L
L
Ourry
A
A
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
D009584:Nitrogen