INTERACTIVE EFFECTS OF ELEVATED CO2 AND O-3 ON PHOTOSYNTHESIS AND BIOMASS PRODUCTION OF CLONAL 5-YEAR-OLD NORWAY SPRUCE [PICEA-ABIES (L) KARST] UNDER DIFFERENT NITROGEN NUTRITION AND IRRIGATION TREATMENTS

To study the: single and combined effects of elevated carbon dioxide ( CO2), ozone (O-3), nitrogen nutrition, and water supply on photosynthe tic gas exchange and biomass accumulation of Norway spruce, a four-fac torial experiment was conducted in closed environmental chambers. Each factor was applied at two levels: (i) ambient and elevated (ambient 200 mu l l(-1)) CO2, (ii) 20 and 80 nl l(-1) O-3. (iii) low and high nitrogen fertilization, and (iv) a well watered and a drought treatmen t. Neither elevated O-3 nor CO2 significantly changed stomatal conduct ances of spruce needles. Adverse effects of elevated O-3 on photosynth etic parameters such as net assimilation rate and carboxylation effici ency occurred only when tile plants were well watered and in a good nu tritional status, After 6 weeks enhanced atmospheric CO2 resulted in i ncreased net assimilation rates provided that nutrition was well balan ced and plants were well watered, Acclimation processes became apparen t and are interpreted as a consequence of sink regulation. While O-3 e ffects were apparent only in biomass of 1-year-old plant material. ele vated CO2-resulted in higher biomass of the buds expanding during the exposure and increased root biomass significantly. Above- and below-gr ound biomass were strongly influenced by the water and nutrition treat ments.