15NO3 assimilation by the field Pea Pisum sativum L.

The objectives of this study were to determine the effect of low mineral supply on plant growth and the uptake and redistribution of mineral N by different plant organs according to the period of uptake. A glasshouse study was conducted on two pea genotypes, L833 and cv. Frisson, fed without or with 4 mM NO3. Plants fed with 4 mM N were labelled for 5 days with N-15 at three stages: 7 leaf stage, beginning of flowering, and beginning of seed filling. Plants were harvested at day 6 and at later stages. The results indicated for the two genotypes that supplying 4 mM N to the plants significantly increased their total dry weight up to the beginning of seed filling, whereas nodule dry weight was reduced. Genotype differences in N uptake and redistribution among plant organs were minor. When plants were labelled with N-15 at early stages of growth, about 60% of total plant N-15 was located in leaves. At maturity the proportion of N-15 recovered in seeds was about 60% for both genotypes. When plants were labelled at the beginning of seed filling, N-15 was mainly located in young organs such as upper leaves, pods and seeds. During seed fill the remobilisation of N-15 to seeds occurred from all organs of the plant. At physiological maturity about 70% of N-15 was located in seeds.