Effects of roadside conditions on plants and insects. II. Soil conditions.
The performance of Lolium perenne plants grown in roadside soil in the absence of roadside atmospheric conditions was studied. Significantly fewer plants germinated in soil taken 0.6 m from the carriageway compared with soil taken 6 m from the carriageway. When plant populations were equal, plants grown in soil taken from beside the carriageway attained greater DW and a greater soluble N content. Aphids (Rhopalosiphum padi) on the plants grew more rapidly and had greater fecundity on plants grown in soil taken beside the carriageway. NOxabsorbed by roadside soil was probably the cause of these effects. The effects may also have been related to the greater de-icing salt concn in roadside soil. An experiment with different NaCl concn showed no effect on L. perenne foliage DW or on any life-history parameter of R. padi. However, salt may play a role in the absorption of NOxby soils, its subsequent oxidation and hence its availability to plants.