EFFECT OF ATMOSPHERIC AMMONIA ON THE NITROGEN-METABOLISM OF SCOTS PINE (PINUS-SYLVESTRIS) NEEDLES

Four-year-old seedlings of Scots pine (Pinus sylvestris L.) were expos ed to filtered air (FA), and to FA supplemented with NH3 (60 and 240 m u g m(-3)) in controlled-environment chambers for 14 weeks. Exposure t o the higher NH, concentration resulted in an increased activity of gl utamine synthetase (GS, EC 6.3.1.2), and an increase in the concentrat ions of soluble proteins, total nitrogen, free amino acids and leaf pi gments in the needles. The GS activity (mu mol g(-1) fresh weight h(-1 )) in the needle extract increased to levels 69% higher than in FA and the soluble protein concentration to levels 22% higher. Total nitroge n concentration in the needles was 42% higher than in FA, while the fr ee amino acid concentration was 300% higher, which was caused by an in crease in arginine, glutamate, aspartate and glutamine. Chlorophyll a, chlorophyll b and carotenoid concentrations were 29, 38 and 11% highe r, respectively. Neither the glutamate dehydrogenase (GDH, EC 1.4.1.2) activity nor the concentrations of free NH4+ and glucose in the needl es were affected by exposure to NH3. After NH3 fumigation at 240 mu g m(-3), the starch concentration decreased by 39% relative to the FA. T he results indicate that the metabolism of Scots pine acclimates to co ncentrations of NH3 which an 3 to 10 times higher than the average con centration in areas with intensive stock farming. The possible mechani sms underlying acclimation to NH3 are discussed.