The epistomatal wax crystalloids of potted spruce plants exposed for 20 weeks to motor vehicle emissions along roadside and in a fumigation chamber were studied in the scanning electron microscope. An accelerated structural degradation of the wax crystalloids was observed in comparison with control plants. This structural degradation is considered to cause a structural obstruction of the stomatal antechambers and to contribute to the observed reduction of gas exchange.

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Summary. Six-year-old Norway spruce trees of the same clone were exposed for 10 weeks at the edge of a highway and compared with controls kept in an unpolluted area within 15 km of the first site. Significant differences could be observed with respect to growth, photosynthesis and transpiration rate, all of which were reduced after exposure at the highway.Key words. Exhaust emissions; highway; motor vehicles; Norway spruce; photosynthesis; transpiration.Emissions from motor vehicles are frequently claimed to be major contributors to air pollution, with noxious effects on trees. However, few investigations have been carried out specifically on the toxicity of emissions for trees. Fumigations under controlled conditions were performed by F1/ickiger et al. ~ who demonstrated an inhibition of the regulatory ability of the stomata of Populus tremula leaves. Kammerbauer et al.; studied the impairment of photosynthetic capacity and stomatal regulation in Norway spruce, which was not observed when a catalytic converter was used. Field experiments with grafts of Norway spruce were carried out by Keller 3. Trees kept at roadsides with heavy traffic showed an inhibition of CO2-uptake by 40 % compared to nursery controls after only 13 weeks. At the same time, peroxidase activity was significantly depressed. Visible symptoms such as color changes of the needles could not be observed. We report here an experiment with 6-year-old Norway spruce trees from the same clone which were exposed to roadside conditions for 10 weeks. The control site was essentially free of motor vehicle emissions. A comparison revealed significant differences in growth in length, photosynthetic parameters and transpiration. , six-year-old trees were placed within 5 m of the A 9 motorway (Mfinchen-Nfirnberg) at Allershausen for 10 weeks. The trees were positioned on the eastern side of the road because of prevailing westerly winds. The plants were lowered into the ground in their containers and watered as required. Five controls were kept close to the Department of Botany (Weihenstephan) 15 km from Allershausen under similar conditions except for the relatively unpolluted location with NO x levels amounting to about one tenth of the concentrations observed at the highway. On August 10, 1986, the samples were removed from the highway and left for 1 day in the control area for adaptation. Then the gas exchange parameters (CO2 uptake, dark respiration and transpiration, under different CO; partial pressures at saturating light intensities, i.e. > 1700 pmol quanta m-2s 5) were measured on twigs in an open system (cuvette size: 140 x 80 x 60 mm 3) by means of an infrared gas analyzer as 2 described in detail elsewhere. The needle volume was taken as a reference. It was determined three times as the water displacement of the same twigs used for gas exchange measurements (circa 15 cm length, two needle years) minus the volume of the shoot axes, which was calculated on the basis of measurements with a vernier caliper. The needle area was calculated from the mea...

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