SUMMARYClotied cuttings oi Betula pendula Roth were grown in field fumigation chambers at Birmensdorf throughout one growing season in filtered air with either < 3 (control) or 90/40 nl 1"^ O^ (day/night; ozone generated from pure oxygen). Each ozone regime was split into high and low soil nutrient regimes by watering plants with either a 0-05''[, or a 0-005 "o solution of a fertilizer which contained macronutrients and micronutrients.Fertilization had a strong effect on plant growth, enzyme activities and the expression of ozone-induced effects at the biochemical level. The activities of PEPC and Rubisco were enhanced about threefold in the plants with high fertilization (HF). Significant effects of ozone were in most cases found only in the older leaves of the plants with low fertilization (LF). There, sucrose, glucose and fructose levels were enhanced. In both fertilization treatments, the number of starch granules along the minor veins was increased. These ozone effects point to a decreased or inhibited phloem loading. The increased PEPC activity and the enhanced tnalate levels in the ozoneexposed plants might be the result of a redirection of carbon flow from sucrose synthesis and translocation towards anapieurotic processes, which can feed detoxification and repair of ozone injury as indicated by enhanced respiration. These findings agree well with the observed effects of ozone in lowering the root: shoot biomass ratio. Although there was a marked reduction in the O^/LF plants, O^/HF plants showed no significant response. Inositol was decreased under ozone exposure In both fertilizer treatments, contrasting with the pattern for carbohydrates.These results demonstrate the role of fertilization as an important modifier of ozone-induced effects at the plant biochemical level. Well fertilized plants appear to cope better with the impact of ozone on metabolism.Keywords; Ozone/fertilization interactions, carbohydrates, phosphoenolpynjvate carboxylase, Rubisco, carbon allocation/partitioning, Betula pendula.woody plants with indeterminate growth, mature INTRODUCTION leaves near the stem bases export most of the fixed C Plant grovv'th is the result of a balance between to the lower stem and roots throughout the growing carbon gain, allocation and use. To ensure survival, season (Dickson, 1991 ;Coleman et al., 1995). Not plants have to cope with a variety of environmental surprisingly, ozone, which predominantly affects variables such as ozone or nutrient availability. The these older leaves, often leads to reduced root:shoot basic responses to ozone primarily take place at the ratios, as shown for forest trees such as birch {Betula biochemical and physiological levels in leaves. Nu-pendula, Matyssek et al. (1992)) and poplar {Pop-merous effects on photosynthesis and carbohydrate ulusx euramericana, Matyssek et al. (1993)). Recent metabolism resulting in alterations to translocation results with the same poplar species have revealed and growth have been reported (Darrall 1989). In that there is a dynamic response o...

The effect of ozone, needle age, and season on the pH of homogenate and acid contents of Scots pine and Norway spruce needles is presented. In addition enzyme activities of cytochrome C-oxidase (cyt. C-ox), phosphoenolpyruvate-carboxylase (PEPC), shikimic acid-dehydrogenase (SHDH) and malate-dehydrogenase (MDH) were measured in Scots pine needles. In freshly sprouted spruce needles the level of quinic acid is high and the pH of the needle homogenate is low. Shikimic acid starts at low levels, increases with increasing needle age and becomes dominant, whereas the quinic acid content decreases. Malic acid has a marked seasonal trend; no trend was found in citric acid. Ozone (200 ~g/m 3) decreased shikimic acid and quinic acid, whereas pH, malic acid and citric acid increased. Ozone (100 ~tg/m 3) had a similar effect, except in the current-year spruce needles. In Scots pine needles ozone led to increased enzymatic activities of cyt. C-ox, PEPC and SHDH, and a decrease in the activity of MDH. This effect was more pronounced in summer than in autumn, but the visible damage was greater in autumn. These effects can be found with other stresses and are not specific for ozone.

Summary. Cuttings of hybrid poplar (Populus • euramericana var. "Dorskamp") were exposed to ozone (80 ]xg/m 3 from 2100 hours to 0700 hours, 180 [.tg/m 3 from 0700 hours to 2100 hours) for 3 months. Ozone reduced the starch content in leaves and stem bark, whereas starch granules accumulated in bundle sheath cells along small leaf veins. At the same time, sucrose and inositol content increased in the leaves. Mesophyll cells in the vicinity of the stomata were injured first, and droplet-like material appeared on their walls. In the sieve plates of fumigated trees, the pores showed a higher degree of narrowing than those of the control treatment. Cell collapse in the leaves was accompanied by water loss and an increase in air space. In the stems, the ozone treatment led to a reduced radial width, particularly in the xylem tissue. These results are discussed in relation to reduced or inhibited phloem loading and ozone-induced drought stress. The plants injured by ozone showed quite distinct patterns of metabolite responses as well as enzyme activities (PEP-and RubPcarboxylase) in the leaves from the top to the bottom. There were also remarkable differences in the reaction of sucrose and inositol between leaves and stem bark. Future research should therefore increasingly follow a whole-plant approach for a better understanding of complex plant reactions.

The effect of 100 and 200 t.tg.m -3 (50 and 100 ppb) ozone and ambient air on 4-year-old grafts of a Scots pine clone was tested in closedtop fumigation chambers. Ozone decreased the myo-inositol and inccreased the pinitol levels in the 1-year-old needles, whereas the effect in the current-year needles was less distinct. In neither case did ambient air lead to any detectable effects on these parameters compared with controls. However, there was a pronounced chamber effect in the levels of myo-inositol and pinitol compared with trees standing in the open field, where inositol was higher and pinitol lower. There is some evidence, based on visible symptoms as well as biochemical changes, that season is an important modifier of the effect of ozone on Scots pine.

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