Influence of Nitrogen Availability on Seed Nitrogen Accumulation in Pea

The final seed nitrogen concentration (the ratio of seed N and dry matter content) is highly variable in pea (Pisum sativum L.) and N remobilization during seed filling may limit yield by restricting the seed filling period. This study was conducted to determine how seed N accumulation is regulated in pea. The effect of N availability and distribution on individual seed N accumulation rate at different nodes was investigated in three genotypes grown in the field and glasshouse under various levels of N fertilizer, depodding, and defoliation. The N content of vegetative plants parts (stems, leaves, podwails) and seeds from three mainstem nodes were regularly recorded. Plant N available to the seeds at a given time was assessed as the sum of the amount of N still available for remobilization in vegetative parts and the amount of N accumulated by the plant. The results indicate that the N available in a plant at a given time can be considered as one common pool accessible to all seeds and equitably divided among them. Thus, the rate of individual seed N accumulation was unaffected by intra-plant position of seeds. This rate increased with the amount of N available per seed until a maximum rate of individual seed N accumulation (43 µg [seed.sup.-1] [degree-day.sup.-1]) was reached. The relationship established between the rate of individual seed N accumulation and the plant N available per seed will be useful to improve models simulating yield and final seed N concentration in legumes.
THE SEED NITROGEN CONCENTRATION of pea varies greatly with environment (Karjalainen and Kortet, 1987). Several studies on different species have shown that changes in assimilate availability during the filling period [...]