Abstract
The relationship between the nitrogen and the free amino acid content in Stratiotes aloides L. was investigated for 11 healthy stands in the Netherlands. In the shoots, the mean free asparagine and free arginine levels were strongly correlated with the mean total N concentrations and the ammonium concentrations in the water layer. The percentage of total N present as free amino acids varied from 5.4 % to 27.5 % between the stands. In the stands with the highest total N levels, up to 92 % of the nitrogen in the free-amino acid pool consisted of asparagine and arginine. The results reveal that the accumulation of these N-efficient free amino acids was caused by increased ammonium availability in the environment. The accumulation of specific free amino acids is regarded as an early indication for N-stress in still healthy S. aloides stands.
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