Dependence of seed nitrogen concentration on plant nitrogen availability during the seed filling in pea

The final seed nitrogen (N) concentration of the pea (Pisum sativum L.) Var ies greatly with environment. These variations seem to be related to N avai lability in the plant. To understand such an effect, the pattern of seed N concentration during seed filling was analysed at a given node as the ratio of seed N accumulation rate and seed dry matter accumulation rate. Three e xperiments were conducted in the field and glasshouse. Pea genotypes 'Solar a', 'Frisson' and its non-nodulating mutant 'P2' were grown and different t reatments were applied to manipulate N availability during seed filling. Tr eatments included N supply (addition of N fertiliser), depodding (removal o f pods) and defoliation (removal of leaves). Changing the N availability du ring the seed filling affected the seed N concentration in all experiments. Seed N concentration increased or decreased when plant N availability was enhanced or reduced respectively. The response of seed N concentration to N availability was not caused by variations in the seed dry matter accumulat ion rate, as this rate is fixed at the beginning of the seed filling. Chang es in seed N concentrations were mainly caused by variations in the seed N accumulation rates according to N availability in the plant. The results de monstrate that seed N and dry matter accumulations are not similarly contro lled during seed filling. Unlike the seed dry matter accumulation rate, the seed N accumulation rate at a given node can vary with time and depends ma inly on N availability in the plant regardless of genotype. However, seeds seem to have minimal N requirements (approximately 2.6 mg g(-1) of N) whate ver the genotype. (C) 1999 Elsevier Science B.V. All rights reserved.