THE RELATIONSHIP OF NITRATE REDUCTASE-ACTIVITY TO UPTAKE AND ASSIMILATION OF ATMOSPHERIC (NO2)-N-15-NITROGEN IN NEEDLES OF NORWAY SPRUCE (PICEA-ABIES [L] KARST)

Using (NO2)-N-15, relations between nitrate reductase activity and sto matal conductance, N-15-uptake and N-15-glutamate were studied in the two youngest needles flushes of potted Norway spruce (Picea abies [L.] Karst.). There were linear correlations between the stomatal conducta nce and the N-15-uptake and between the N-15-uptake and nitrate reduct ase (E.C. 1.6.6.1/1.6.6.2) activity. The N-15 labelling of free glutam ate shows the assimilation of NO2 from the atmosphere in addition to t he nitrogen from the soil. The portion of glutamate originating from ( NO2)-N-15 was linearly related to nitrate reductase activity in spring experiments. This indicates that this enzyme activity reflected the r ate of NO2-assimilation.