Uptake and Distribution of NO2 in Norway Spruce (Picea Abies L. Karst.)

Potted spruce trees (Picea abies [L.] Karst.) were fumigated with NO2 or 15NO2 under controlled conditions in constant light. Current and previous flush needles, the bark and the fine roots were analysed for total 15N content and incorporation of 15N into the α-amino nitrogen of free amino acids. In addition, in vitro nitrate reductase activity and stomatal conductance of the needles were measured. In fumigated trees, nitrate reductase activity increased after a lag period of about four hours to levels which were five times higher than in controls exposed to filtered air. After a fumigation period of 24 hours nitrate reductase activity was linearly dependant on the NO2 concentration used for fumigation both in previous and current flush. With an average of 9.1% 15N, 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. 15N labelled amino acids were also detected in the bark and the roots, indicating export from the needles. There were linear correlations between the stomatal conductance and the 15N uptake and between the 15N uptake and nitrate reductase activity