Effects of air pollutant emissions from a rural motorway on Petunia and Trifolium

Abstract

Potted plants of Petunia hybrida (indicator plant for ethene), Trifolium subterraneum (indicator plant for ozone), and Trifolium pratense were grown downwind from a motorway with approximately 30 000 vehicles/day. Petunia plants were grown with two different levels of nutrient supply. Pots with Petunia plants were placed at 10, 20, 40, 80 and 120 m distances from the motorway. The flowers of petunia were significantly smaller close to the motorway. The percentage of ripened fruits was higher close to the motorway, indicating that flowering proceeded faster close to the motorway. The number of aborted flower buds was also greater close to the motorway. Dry weight and nitrogen content did not vary systematically with the distance from the motorway, but were significantly higher in the plants treated with higher nutrient supply. Clover plants were placed at 10, 20, 40, 80 and 200 m distances from the motorway. Towards the end of the experiment, after ozone episodes, visible injury was recorded. This kind of injury was significantly less close to the motorway compared to the 200 m distance. This effect is explained by the fast reaction between nitrogen monoxide and ozone, causing a local depression in the ozone concentration in the vicinity of the motorway. The extent of ozone injury was less in Trifolium pratense compared to T. subterraneum. A type of visible leaf injury, clearly distinguishable from the ozone injury, was observed in Trifolium subterraneum. This second kind of visible injury declined strongly with increasing distance from the motorway, and was almost absent at 200 m distance.