INCORPORATION OF ATMOSPHERIC (NO2)-N-15-NITROGEN INTO FREE AMINO-ACIDS BY NORWAY SPRUCE PICEA-ABIES (L) KARST

During spring and autumn 1991, potted 6-year-old spruce trees (Picea abies (L.) Karst.) were fumigated with 60 nl . l-1 (NO2)-N-15 for 4 days under controlled conditions in constant light. Current and previous flush needles, the bark and the fine roots were analysed for total N-15 content and incorporation of N-15 into the alpha-amino nitrogen of free amino acids. In addition, in vitro nitrate reductase activity and stomatal conductance of the needles were measured. Nitrate reductase activity was significantly higher in the needles of fumigated trees compared to control trees exposed to filtered air. With an average of 9. 1 % N-15, free glutamate was the pool with the most label. Taking into account the time-course of the labelling of this pool, this figure can be taken as an estimate of the minimum contribution of NO2 to the N nutrition of the needles. N-15-labelled amino acids were also detected in the bark and the roots, indicating export from the needles.