EFFECT OF FERTILIZATION ON OZONE-INDUCED CHANGES IN THE METABOLISM OFBIRCH (BETULA-PENDULA) LEAVES

Cloned cuttings of 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 l(-1) O-3 (day/night; ozone gene rated 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 % solution of a fertilizer which contained macronutrients and micr onutrients. Fertilization had a strong effect on plant growth, enzyme activities and the expression of ozone-induced effects at the biochemi cal level. The activities of PEPC and Rubisco were enhanced about thre efold in the plants with high fertilization (HF). Significant effects of ozone were in most cases found only in the older leaves of the plan ts with low fertilization (LF). There, sucrose, glucose and fructose l evels were enhanced. In both fertilization treatments, the number of s tarch granules along the minor veins was increased. These ozone effect s point to a decreased or inhibited phloem loading. The increased PEPC activity and the enhanced malate levels in the ozone-exposed plants m ight be the result of a redirection of carbon flow from sucrose synthe sis and translocation towards anapleurotic processes, which can feed d etoxification and repair of ozone injury as indicated by enhanced resp iration. 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-3/LF plants, O-3/HF plants showed no significant re sponse. Inositol was decreased under ozone exposure in both fertilizer treatments, contrasting with the pattern for carbohydrates. These res ults 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.