NO2-INDUCED NITRATE REDUCTASE-ACTIVITY IN NEEDLES OF NORWAY SPRUCE (PICEA-ABIES) UNDER LABORATORY AND FIELD CONDITIONS

The induction of activity of the enzyme nitrate reductase (NR, EC 1.6. 6.1, 1.6.6.2) in needles of Norway spruce (Picea abies [L.] Karst.) by nitrogen dioxide (NO2) was studied under laboratory and field conditi ons. In fumigation chambers an increase in nitrate reductase activity (NRA) was detected 4 h after the start of the NO2 treatment. During th e first 2 days with 100 mu g NO2 m(-3), NRA reached a constant level a nd did not change during the following 4 days. At the same level of NO 2, NRA was lower in needles from trees grown on NPK-fertilized soil th an on non-fertilized soil. After the transfer of spruce trees from fer tilized soil to NPK-rich nutrient solution, NRA was transiently increa sed. This effect was assigned to root injuries causing nitrate transpo rt to the shoot and subsequent induction of NRA. Neither trees on fert ilized soil nor trees transferred to NPK-poor nutrient solution had in creased NRA unless NO2 was provided. The NO2 gradient in the vicinity of a highway was used to test the long-term effect of elevated levels of NO2 on needle NRA of potted and field-grown spruce trees. Compared with less polluted sites, permanently increased NRAs were detected whe n NO2 concentrations were above 20 mu g m(-3). Controls of field measu rements some 10 years after the introduction of catalytic converters i n cars showed no significant change neither in NO2 levels nor in the d ecreasing NRA of spruce needles with the distance from the highway.