EFFECTS OF AIR POLLUTANT EMISSIONS FROM A RURAL MOTORWAY ON PETUNIA AND TRIFOLIUM

Potted plants of Petunia hybrida (indicator plant for ethene), Trifoli um subterraneum (indicator plant for ozone), and Trifolium pratense we re grown downwind from a motorway with approximately 30 000 vehicles/d ay. Petunia plants were grown with two different levels of nutrient su pply. Pots with Petunia plants were placed at 10, 20, 40, 80 and 120 m distances from the motorway. The flowers of petunia were significantl y smaller close to the motorway. The percentage of ripened fruits was higher close to the motorway, indicating that flowering proceeded fast er close to the motorway. The number of aborted flower buds was also g reater close to the motorway. Dry weight and nitrogen content did not vary systematically with the distance from the motorway, but were sign ificantly higher in the plants treated with higher nutrient supply. Cl over plants were placed at 10, 20, 40, 80 and 200 m distances from the motorway. Towards the end of the experiment, after ozone episodes, vi sible ozone injury was recorded. This kind of injury was significantly less close to the motorway compared to the 200 m distance. This effec t is explained by the fast reaction between nitrogen monoxide and ozon e, causing a local depression in the ozone concentration in the vicini ty of the motorway. The extent of ozone injury was less in Trifolium p ratense compared to T subterraneum. A type of visible leaf injury, cle arly distinguishable from the ozone injury, was observed in Trifolium subterraneum. This second kind of visible injury declined strongly wit h increasing distance from the motorway, and was almost absent at 200 m distance.