During one growing period, 5‐year‐old spruce trees (Picea abies L., Karst.) were exposed in environmental chambers to elevated concentrations of carbon dioxide (750 cm3 m−3) and ozone (008 cm3 m−3) as single variables or in combination. Control concentrations of the gases were 350cm3 m−3CO2 and 0.02 cm3 m −3 ozone. To investigate whether an elevated CO2 concentration can prevent adverse ozone effects by reducing oxidative stress, the activities of the protective enzymes superoxide dismutase, catalase and peroxidase were determined. Furthermore, shoot biomass, pigment and protein contents of two needle age classes were investigated. Ozone caused pigment reduction and visible injury in the previous year's needles and growth reduction in the current year's shoots. In the presence of elevated concentrations of ozone and CO2, growth reduction in the current year's shoots was prevented, but emergence of visible damage in the previous year's needles was only delayed and pigment reduction was still found. Elevated concentrations of ozone or CO2 as single variables caused a significant reduction in the activities of superoxide dismutase and catalase in the current year's needles. Minimum activities of superoxide dismutase and catalase and decreased peroxidase activities were found in both needle age classes from spruce trees grown at enhanced concentrations of both CO2 and ozone. These results suggest a reduced tolerance to oxidative stress in spruce trees under conditions of elevated concentrations of both CO2 and ozone.

SUMMARYFive days after emergence radish {Raphanus sativus L. cv. Cherry Belle) plants were transferred to a phytotron at the GSF Munchen, where they were exposed in four large controlled climate chambers to two atmospheric concentrations of COj ('ambient', daily means of % 385 //mol mol'; elevated, daily means of « 765 //mol mol ') and two O3 regimes ('non-polluted' air, 24 h mean of 20 nmol mo! '; polluted air, 24 h mean of 73 nmol mol"'). Leaf gas-exchange measurements were made at intervals, and visible O3 damage, effects on growth, dry matter partitioning and mineral composition were assessed at a final whole-plant harvest after 27 d. In 'non-polluted air' CO2 enrichment resulted in a progressive stimulation in A^^^, whilst there was a decline in g^ which decreased E (i.e. improved WUE,). The extra carbon fixed in elevated CO2 stimulated growth of the root (-h hypocotyl) by 43 °o, but there was no significant effect on shoot growth or leaf area. Moreover, a decline in SLA and LAR in COj-enriched plants suggested that less dry matter was invested in leaf area expansion. Tissue concentrations of N, S, P, Mg and Ca were lower (particularly in the root+ hypocotyl) m elevated CO.,, indicating that total uptake of these nutrients was not affected by CO.,, and there was an increase in the C: N ratio in root (+ hypocotyl) tissue. In contrast, O3 depressed A^^^ (« 26 "o) and induced slight stomatal closure, with the result that WUEj declined. All plants exposed to 'polluted' air developed typical visible symptoms of O3 injury, and effects on carbon assimilation were reflected in reduced growth, with shoot growth maintained at the expense of the root. In addition, O,, increased the P and K concentration in shoot and root ( +hypocotyl) tissue, indicating enhanced uptake of these nutrients from the growth medium. However, there was no affect of O3 on tissue concentrations of N, S, Mg and Ca. Interactions between the gases were complex, and often subtle. In general, elevated COj counteracted (at least in part) the detrimental effects of phytotoxic concentrations of O3, whilst conversely, O.j reduced the impact of elevated CO^. Moreover, there were indications that cumulative changes in source: sink relations in 03-exposed plants may limit plant response to COj-enrichment to an even greater extent in the longterm. The future ecological significance of interactions between CO., and O3 are discussed.

No abstract

Two clones of 5-year-old Norway spruce [Picea abies (L.)Karst.] were exposed to two atmospheric concentrations of CO2 (350 and 750/imol moP*) and O3 (20 and 75nmolmor') in a phytotron at the GSF-Forschungszentrum (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 wellfertilized or K-deflcient. 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 (hy 33%) the rate of photosynthesis in the current year's needles. However, O3 depressed (by 30%) the photosynthetic 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 flndings. 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 CO2*soil 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 O3treated 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 con...

No abstract