The Relationship of Nitrate Reductase Activity to Uptake and Assimilation of Atmospheric¹⁵NO₂-Nitrogen in Needles of Norway Spruce (<i>Picea abies</i>[L.] Karst.)

Abstract

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