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

Abstract

The final seed nitrogen (N) concentration of the pea ( Pisum sativum L.) varies greatly with environment. These variations seem to be related to N availability 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 experiments were conducted in the field and glasshouse. Pea genotypes ‘Solara’, ‘Frisson’ and its non-nodulating mutant ‘P2’ were grown and different treatments were applied to manipulate N availability during seed filling. Treatments included N supply (addition of N fertiliser), depodding (removal of pods) and defoliation (removal of leaves). Changing the N availability during 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 accumulation rate, as this rate is fixed at the beginning of the seed filling. Changes in seed N concentrations were mainly caused by variations in the seed N accumulation rates according to N availability in the plant. The results demonstrate that seed N and dry matter accumulations are not similarly controlled 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 mainly 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) whatever the genotype.