Well-supplied and K-deficient 4-year-old clonal Norway spruce trees were exposed to combinations of two levels of ozone (20 and 80 nl l – 1 O3) and carbon dioxide (350 and 750 μl l – 1 CO2) to study the effects of possible future climate factors on gas exchange characteristics. The fumigation was performed in environmental chambers for a complete growing season. After the exposure, plants were cultivated outdoors to investigate possible recovery and delayed effects. During the exposure 1-year-old needles responded to the 80 nl l – 1 O3 treatment by a sharp but transient decrease of both apparent carboxylation efficiency (CE) and maximum photosynthetic capacity (A2500). Elevated CO2 also reduced CE and A2500. The effect became stronger in the course of the exposure and was accompanied by decreases of N and P as well as chlorophyll contents. In case of K deficiency, the acclimation response of current-year needles was even more pronounced reflecting lower sink capacities for carbon metabolites. The joint application of elevated O3 and CO2 resulted in the lowest values of gas exchange parameters and chlorophyll contents. At the beginning of the growing season after the exposure and under outdoor conditions, all these treatment effects disappeared in the needles which had developed during the fumigation. In the course of the development of the new flush, however, the well-supplied 1-year-old needles which had been treated with 80 nl l – 1 O3 and 350 μl l – 1 CO2 in the year before, exhibited a sharp decline of CE and A2500. Simultaneously, chlorotic mottle and bands developed. These delayed symptoms are discussed in the context of the previously published “memory” effect for O3 (Sandermann et al. 1989). Additionally, evidence is presented that shoot development is altered in plants which had been exposed to elevated O3.

To study the single and combined effects of elevated carbon dioxide (CO2), ozone (O3), nitrogen nutrition, and water supply on photosynthetic gas exchange and biomass accumulation of Norway spruce, a four-factorial experiment was conducted in closed environmental chambers. Each factor was applied at two levels: (i) ambient and elevated (ambient + 200 μl 1-1) CO2, (ii) 20 and 80 nl 1-1 O3, (iii) low and high nitrogen fertilization, and (iv) a well watered and a drought treatment. Neither elevated O3 nor CO2 significantly changed stomatal conductances of spruce needles. Adverse effects of elevated O3 on photosynthetic parameters such as net assimilation rate and carboxylation efficiency occurred only when the plants were well watered and in a good nutritional status. After 6 weeks enhanced atmospheric CO2 resulted in increased net assimilation rates provided that nutrition was well balanced and plants were well watered. Acclimation processes became apparent and are interpreted as a consequence of sink regulation. While O3-effects were apparent only in biomass of 1-year-old plant material, elevated CO2 resulted in higher biomass of the buds expanding during the exposure and increased root biomass significantly. Above and below-ground biomass were strongly influenced by the water and nutrition treatments.

SUMMARY Two clones of 5-yr-old Norway spruce (Picea abies [L.] Karst.) were exposed to two atmospheric concentrations of CO2 (350 and 750 ,tmol mol-') and of 03 (20 and 75 nmol mol-V) in a phytotron at the GSFForschungszentrum (Munich) over the course of a single season (April-October). The phytotron was programmed to recreate an artificial climate similar to that at a high elevation site in the Inner Bavarian forest, and trees were grown in 40 1 containers of soil (pH 3 5) fertilized to achieve two levels of potassium nutrition; well fertilized and K-deficient. Foliar nutrient analyses performed at the beginning of the exposure indicated that the fertilization programmes achieved their goal without significantly altering the levels of other nutrients or the soil pH. At the beginning of the fumigation, foliar K concentrations were 7-9 mg g-1 d. wt for well fertilized trees and 4-5 mg g-1 d. wt for trees receiving no supplemental K. Over the course of the season, differences between K treatments intensified so that by the end of the experiment there was a five to sixfold difference between foliar K concentrations. This was associated with slight, but significant (P < 0 05), decreases in S and Zn (and of Cu in the 1989 needle year age class) and higher levels of C, N and Mg in K-deficient trees. Foliar N concentrations were low for all trees (9-15 mg g-1 needle d. wt) but were similar to levels found in the field. Elevated 03 was found to decrease significantly the C (P < 0 05) and N (P < 0 001) content of both current-year (1989) and previous-year (1988) needles independent of CO2 concentration, but apart from some minor changes in the concentrations of Cu and Mn in the current-year needles no other effects of the pollutant on plant nutrient status were found. In contrast, CO2 enrichment resulted in significantly (P < 0-01) lower concentrations of K and P (effects on Mg were also on the borderlines of statistical significance) in current-year needles, but there was no influence on the nutrient composition of the previous-year needles (although effects on N were on the borderlines of statistical significance). CO2 enrichment also increased (P < 005) the C: N ratio of both current-year and previous-year needles. One factor contributing to the decline in foliar K at elevated CO2 appeared to be a marked increase (25-30 %) in the rate at which cations were leached from the canopy by repeated simulated acid mist (pH 4 0) events, and this effect occurred independently of the 03 concentration. The information presented will aid the interpretation of parallel studies examining the effects of elevated CO2 and/or 03 on seasonal changes in photosynthesis, non-structural carbohydrate content, antioxidants, tree growth and water use efficiency, and sheds further light on the growing scepticism concerning the role of 03 in the development of Mg and K-deficiency symptoms characteristic of certain types of forest decline in central Europe.

Two clones of 5-yr-old Norway spruce (Picea abies [L.] Karst.) were exposed to two atmospheric concentrations of CO 2 (350 and 750 μmol mol -1 ) and of O 3 (20 and 75 nmol mol -1 ) in a phytotron at the GSF-Forschungszentrum (Munich) over the course of a single season (April-October). The phytotron was programmed to recreate an artificial climate similar to that at a high elevation site in the Inner Bavarian forest, and trees were grown in 40 1 containers of soil (pH 3.5) fertilized to achieve two levels of potassium nutrition ; well fertilized and K-deficient. Foliar nutrient analyses performed at the beginning of the exposure indicated that the fertilization programmes achieved their goal without significantly altering the levels of other nutrients or the soil pH. At the beginning of the fumigation, foliar K concentrations were 7-9 mg g -1 d. wt for well fertilized trees and 4-5 mg g -1 d. wt for trees receiving no supplemental K. Over the course of the season, differences between K treatments intensified so that by the end of the experiment there was a five to sixfold difference between foliar K concentrations. This was associated with slight, but significant (P < 0.05), decreases in S and Zn (and of Cu in the 1989 needle year age class) and higher levels of C, N and Mg in K-deficient trees. Foliar N concentrations were low for all trees (9-15 mg g -1 needle d. wt) but were similar to levels found in the field. Elevated O 3 was found to decrease significantly the C (P < 0.05) and N (P < 0.001) content of both current-year (1989) and previous-year (1988) needles independent of CO 2 concentration, but apart from some minor changes in the concentrations of Cu and Mn in the current-year needles no other effects of the pollutant on plant nutrient status were found. In contrast, CO 2 enrichment resulted in significantly (P < 0.01) lower concentrations of K and P (effects on Mg were also on the borderlines of statistical significance) in current-year needles, but there was no influence on the nutrient composition of the previous-year needles (although effects on N were on the borderlines of statistical significance). CO 2 enrichment also increased (P < 0.05) the C :N ratio of both current-year and previous-year needles. One factor contributing to the decline in foliar K at elevated CO 2 appeared to be a marked increase (25-30%) in the rate at which cations were leached from the canopy by repeated simulated acid mist (pH 4.0) events, and this effect occurred independently of the O 3 concentration. The information presented will aid the interpretation of parallel studies examining the effects of elevated CO 2 and/or O 3 on seasonal changes in photosynthesis, non-structural carbohydrate content, antioxidants, tree growth and water use efficiency, and sheds further light on the growing scepticism concerning the role of O 3 in the development of Mg and K-deficiency symptoms characteristic of certain types of forest decline in central Europe.

An exposure — response study with proportionalto-ambient ozone levels was conducted in closed chambers on 3-year-old European beech (Fagus sylvatica L.) of montane origin. The fumigation started in April 1990 and lasted for a single growing season. Climate data and ozone concentrations monitored at an experimental station of the Institute for Applied Plant Biology, Schönenbuch, Switzerland were simulated in the exposure chambers 12 days later (1*O3). To test exposure-response relations three additional treatments were applied, subambient (0.2*O3) and two proportionally increased ozone treatments (1.5*O3 and 2*O3). The photosynthetic behaviour of the trees in August revealed the light reactions to be less affected than parameters which are related to the dark reactions of photosynthesis. Assimilation (A350), apparent carboxylation efficiency (CE), and maximum photosynthetic capacity (A2500) were reduced with increasing ozone concentration. For the ozone response of CE and A2500 ‘Critical Levels’ were calculated.

ABSTRACTTwo clones of 5‐year‐old Norway spruce [Picea abies (L.) Karst.] were exposed to two atmospheric concentrations of CO2 (350 and 750 μmol mol−1) and O3 (20 and 75nmolmol−1) in a phytotron at the GSF‐Forschung‐szentrum (Munich) over the course of a single season (April to October). The phytotron was programmed to recreate an artificial climate similar to that at a high elevation site in the Inner Bavarian Forest, 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 assimilation were made on individual needle year age classes over the course of the season, chlorophyll fluorescence kinetics were recorded after approximately 23 weeks, and seasonal changes in non‐structural carbohydrate composition of the current year's foliage were monitored. Ozone was found to have contrasting effects on the rate of net CO2 assimilation in different needle age classes. After c. 5 months of fumigation, elevated O3 increased (by 33%) the rate of photosynthesis in the current year's needles. However, O3 depressed (by 30%) the photo‐synthetic rate of the previous year's needles throughout the period of exposure. Chlorophyll fluorescence measurements indicated that changes in photosystem II electron transport played no significant role in the effects of O3 on photosynthesis. The reasons for the contrasting effects of O3 on needles of different ages are discussed in the light of other recent findings. Although O3 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 content of the needles. The transfer 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 growth, the photosynthetic rate of the previous year's foliage declined. The extent of photosynthetic adjustment in response to prolonged exposure to elevated CO2 depended upon the clone, providing evidence of intraspecific variation in the long‐term response of photosynthesis to elevated CO2. The increase in photosynthesis induced by CO2 enrichment was associated with increased foliar concentrations of glucose, fructose and starch (but no change in sucrose) in the new growth. CO2 enrichment significantly enhanced the photosynthetic rate of K‐deficient needles, but there was a strong CO2soil interaction in the current year's needles, indicating that the long‐term response of trees to a high CO2 environment may depend on soil fertility. Although the rate of photosynthesis and non‐structural carbohydrate content of the new needles were increased in O3‐treated plants grown at higher levels of CO2, there was no evidence that elevated CO2 provided additional protection against O3 damage. Simultaneous exposure to elevated O3 modified the effects of elevated CO2 on needle photosynthesis and non‐structural carbohydrate content, emphasizing the need to take into account not only soil nutrient status but also the impact of concurrent increases in photochemical oxidant pollution in any serious consideration of the effects of climate change on plant production.