RESPONSES OF PHOTOSYNTHESIS, CARBOHYDRATES AND ANTIOXIDANTS IN NEEDLES OF NORWAY SPRUCE TO SLOW AND RAPID CHANGES IN OZONE

The goal of the present study was to examine the effects of slow and r apid changes of ozone (O-3) concentrations on the physiological behavi our of current-year needles of Norway spruce (Picea abies (L.) Karst.) . For this purpose five-year-old spruce seedlings were exposed in grow th chambers for 49 days to either charcoal-filtered air, slowly increa sing O-3 concentrations from zero up to 100 nl l(-1) in weekly steps o f 25 nl l(-1), or immediately to 100 nl l(-1) of O-3. During the inves tigation period gas exchange, carbohydrate and antioxidant contents of the current flush were measured. In needles which experienced slowly increasing O-3 concentrations, cumulative O-3 uptake was approximately 30% lower than in needles continuously fumigated with 100 nl l(-1) of O-3. The higher O-3 uptake in the permanent 100 nl l(-1) O-3 treatmen t caused a pronounced decline in net photosynthesis, in the efficiency of CO2 uptake and in the starch content of the seedlings. Initially t he ascorbate pool increased, but after 5 weeks of exposure ascorbate c oncentrations declined and were comparable to values obtained in charc oal-filtered controls, while the thiol contents were enhanced during f umigation with permanent 100 nl l(-1) O-3. On the contrary, slowly inc reasing O-3 caused a significant increase in total needle ascorbate th roughout the fumigation period, which probably prevented an O-3-induce d decline in the photosynthetic machinery as photosynthesis was not af fected although the thiol contents were not enhanced. Furthermore, sta rch content was slightly higher than in O-3-free controls. These resul ts suggest that seedlings of Norway spruce have the possibility to acc limate to O-3 stress, as slowly increasing O-3 concentrations seemed t o increase resistance and the seedlings were able to compensate.