Ammonia Volatilization in Relation to Nitrogen Nutrition of Young Braßica napus Plants Growing with Controlled Nitrogen Supply

Abstract

Summary Brasica napus plants were grown for a period of up to 6 weeks in solution culture with exponentially increasing amounts of nitrate at three different relative addition rates. In some of the experiments nitrate was replaced by ammonium during the last 3 days before measurements of shoot gas exchange and root nitrogen absorption. The contents of nitrate, ammonium and total nitrogen in shoots and roots increased with increasing relative addition rates. Uptake rates of nitrate and ammonium at an external concentration of 1 mM decreased with increasing plant N status. Ammonia emision from the shoots was measured on-line by use of an automatic NH 3 monitor. The emision ranged from 0.1 to 1.7 nmol m -2 leaf surface s -1 and was higher in ammonium than in nitrate supplied plants. Inhibition of glutamine synthetase by addition of 0.5 mM methionine sulphoximine markedly increased the amount of ammonia emitted from the leaves, indicating the importance of this enzyme in controlling the ammonia concentration in plant tisues.