The Relationship of Nitrate Reductase Activity to Uptake and Assimilation of Atmospheric 15NO2-Nitrogen in Needles of Norway Spruce (Picea abies [L.] Karst.)

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.