GASEOUS AMMONIA COUNTERACTS THE RESPONSE OF SCOTS PINE NEEDLES TO ELEVATED ATMOSPHERIC CARBON-DIOXIDE

Four-year-old saplings of Scots pine (Pinus sylvestris L.) were expose d for 8 wk in controlled-environment chambers to charcoal-filtered air (FB), FA supplemented with 754 mg m(-3) (650 mu l l(-1)) CO2, FA supp lemented with 100 mu g m(-3) NH3 and FA + CO2 + NH3. Elevated CO2 indu ced a significant increase in the concentrations of NH4+ and NO3- in t he soil solution, while exposure to NH3 enhanced the soil NH4+ concent ration. Elevated CO2 significantly increased needle biomass and area, and decreased specific leaf area (SLA) and N concentration in the need les. The activity of peroxidase (POD) was decreased, while the activit ies of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) wer e only slightly affected. Gaseous NH3 enhanced the concentration of N, soluble proteins and the GS activity in the needles, while it decreas ed the POD and GDH activities. The effects of elevated CO2 + NH3 on ne edle biomass production, N metabolism and POD activity were smaller th an the effects of single exposures to elevated CO2 or NH3, suggesting that elevated CO2 and NH3 counteract each other and disturb needle phy siology. The possible mechanisms underlying the negative interactions of elevated CO2 and NH3 are discussed. The expected stimulation of bio mass production by elevated CO2 may be reduced in the presence of atmo spheric NH3.