The project aims at evaluating the environmental impact of large emissions of nitrogen oxides into the environment concerning effects on growth, senescence processes and cellular injury in trees (poplar, pine and spruce).


In many forests throughout Europe, trees are exposed to increasing concentrations of ozone and hydroperoxides together with elevated inputs of nitrogen. Free radical production and/or formation of hydroperoxides, from reactions between ozone and unsaturated hydrocarbons produced in plants, are suspected to be responsible for the phytotoxicity of ozone. In both long-term and short-term experiments with poplar and pine, this will be examined for reaction products of these reactions, formation of free radicals, aldehydes and monocarbonic acids, and the expression of the antioxidant enzymes, ascorbate peroxidase, glutathione reductase, superoxide dismutase, catalase and their regulation by the phytohormone ethylene. In these experiments, plants will also be subjected to different levels of nitrogen to investigate imbalancing of other nutrients and how the toxicity of ozone and/or hydrogen peroxide may be modified. In these experiments, iron, manganese and/or zinc will be of special interest, as these trace nutrients are essential constituents of these antioxidant enzymes and necessary for their functioning. How they also protect plants against exposure to ambient concentrations of ozone and/or hydroperoxides will be assessed in plants deficient in these elements. Finally, these results will be compared with those exposed to organic hydroperoxides as these have also been reported to be inhibitory to these enzymes. Furthermore, these effects of ozone will also be assessed in the presence or absence of low concentrations of NO (2-5 ppb) as the presence of such low concentrations of NO have been suggested to be required for ozone toxicity.