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

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.

Nitrogen use efficiency in rapeseed. A review

“…This was confirmed by several studies performed in the field that showed that postflowering nitrogen uptake efficiency had a significant effect on total NUE and that this period was the most important phase in discriminating varieties in terms of yield (Berry et al 2010;Schulte auf'm Erley et al 2011;Ulas et al 2013). More precisely, Malagoli et al (2005a) showed that 30 % of the total plant N of a genotype grown in field conditions was absorbed during seed filling, even though this represented only 27 % of the total seed N. However, to our knowledge, no study of rapeseed has associated nitrogen …”

“…During flowering, the vegetative plant segments switch from being sink organs to source organs, with associated modifications in the N fluxes from older to younger tissues and to the reproductive organs (Le Deunff and Malagoli 2014). Labeling studies in Arabidopsis thaliana (Taylor et al 2010) and B. napus (Rossato et al 2001;Malagoli et al 2005a) showed that the N accumulated in the seeds at harvest originates mainly from the degradation of proteins in vegetative plant segments. phase sequentially, multiple overlapping source-sink situations are possible in rapeseed.…”

“…Pictures of winter oilseed rape taken in autumn (a), in spring (b), with a detail of one floral spike (c), and before harvest (d). A sample of seeds (e) important N losses of 2-3.5 % of the fallen leaves' dry weight (Malagoli et al 2005a).…”

“…2). From the flowering stage onward, leaves are no longer produced, and the onset of senescence occurs quickly, with leaves showing different remobilization ability depending upon their position on the main stem (Malagoli et al 2005a). In parallel, photosynthetic activity is partly ensured by the pod area index.…”

“…Nevertheless, the ratio of plant N content to supplied N does not usually exceed 50 to 60 % in rapeseed (Malagoli et al 2005a). As a consequence, a major problem is the large N surplus, which represents a significant shortfall for farmers and has negative environmental impacts.…”