COMBINED EFFECTS OF GASEOUS AMMONIA AND SULFUR-DIOXIDE ON THE NITROGEN-METABOLISM OF THE NEEDLES OF SCOTS PINE TREES

Three-year old seedlings of Scots pine (Pinus sylvestris) were exposed for twelve weeks in controlled-environment chambers to filtered air ( FA), to FA supplemented with SO2 (75 mu g m(-3)), with NH3 (68 or 258 mu g m(-3)) or with mixtures of SO2 + NH3 (75 + 72 mu g m(-3) or 75 265 mu g m(-3)). The effects of exposure of the trees to the fumigatio n treatments on the activity of glutamine synthetase (GS, EC 6.3.1.2) and glutamate dehydrogenase (GDH, EC 1.4.1.2) in the needles was studi ed as well as the needle concentrations of soluble protein, leaf pigme nts and N, P, K, Mg and Ca. N metabolism of Scots pine needles was par tly inhibited ty SO2 and it was stimulated by NH3. Twelve weeks of exp osure to NH3 increased the activity of GS and the concentrations of so luble protein, chlorophyll a (Chl a) and N, compared to FA. Our result s indicate that elevated atmospheric NH3 can be metabolized by the nee dles of Scots pine. Exposure to SO2 resulted in a decreased activity o f GS, lower concentrations of soluble protein, leaf pigments and P and K, and an increased activity of GDH. Simultaneous exposure to NH3 + S O2 did not cause significant interactive effects on any of the paramet ers studied. The positive effect of NH3 on the needle concentrations o f N and CHl a and on the activity of GS in the needles, counteracted t he negative effects of SO2. The nutrient balance in the needles was af fected by both gases, since NH3 increased the concentration of N and S O2 decreased the concentrations of P and K. A mixture of NH3 + SO2 mig ht cause serious nutrient imbalance in shoots if the soil is unable to meet the increased demands for nutrients in shoots.