EFFECTS OF ELEVATED CO2, ELEVATED O-3 AND POTASSIUM-DEFICIENCY ON NORWAY SPRUCE [PICEA-ABIES (L) KARST] - SEASONAL-CHANGES IN PHOTOSYNTHESIS AND NONSTRUCTURAL CARBOHYDRATE CONTENT

Two clones of 5-year-old Norway spruce [Picea abies (L.) Karst.] were exposed to two atmospheric concentrations of CO2 (350 and 750 mu mol m ol(-1)) and O-3 (20 and 75 nmol mol(-1)) in a phytotron at the GSF-For schungszentrum (Munich) over the course of a single season (April to O ctober), The phytotron was programmed to recreate an artificial climat e similar to that at a high elevation site in the Inner Bavarian Fores t, and trees were grown in Large containers of forest soil fertilized to achieve contrasting levels of potassium nutrition, designated well- fertilized or K-deficient. Measurements of the rate of net CO2 assimil ation were made on individual needle year age classes over the course of the season, chlorophyll fluorescence kinetics were recorded after a pproximately 23 weeks, and seasonal changes in non-structural carbohyd rate composition of the current year's foliage were monitored. Ozone w as found to have contrasting effects on the rate of net CO2 assimilati on in different needle age classes. After c. 5 months of fumigation, e levated O-3 increased (by 33%) the rate of photosynthesis in the curre nt year's needles, However, O-3 depressed (by 30%) the photosynthetic rate of the previous year's needles throughout the period of exposure, Chlorophyll fluorescence measurements indicated that changes in photo system II electron transport played no significant role in the effects of O-3 on photosynthesis, The reasons for the contrasting effects of O-3 on needles of different ages are discussed in the light of other r ecent findings, Although O-3 enhanced the rate at which CO2 was fixed in the current year's foliage, this was not reflected in increases in the non-structural carbohydrate ate content of the needles, The transf er of ambient CO2-grown trees to a CO2-enriched atmosphere resulted in marked stimulation in the photosynthetic rate of current and previous year's foliage, However, following expansion of the current year's gr owth, the photosynthetic rate of the previous year's foliage declined, The extent of photosynthetic adjustment in response to prolonged expo sure to elevated CO2 depended upon the clone, providing evidence of in traspecific variation in the long-term response of photosynthesis to e levated CO2, The increase in photosynthesis induced by CO2 enrichment was associated with increased foliar concentrations of glucose, fructo se and starch (but no change in sucrose) in the new growth, CO2 enrich ment significantly enhanced the photosynthetic rate of K-deficient nee dles, but there was a strong CO2soil interaction in the current year' s needles, indicating that the long-term response of trees to a high C O2 environment may depend on soil fertility, Although the rate of phot osynthesis and non-structural carbohydrate content of the new needles were increased in O-3-treated plants grown at higher levels of CO2, th ere was no evidence that elevated CO2 provided additional protection a gainst O-3 damage, Simultaneous exposure to elevated O-3 modified the effects of elevated CO2 on needle photosynthesis and non-structural ca rbohydrate content, emphasizing the need to take into account not only soil nutrient status but also the impact of concurrent increases in p hotochemical oxidant pollution in any serious consideration of the eff ects of climate change on plant production.