Effects of Roadside Conditions on Plants and Insects. I. Atmospheric Conditions

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Abstract
(1) Effects of the roadside atmosphere were investigated by placing pots of Lolium perenne (L.) at different distances from the roadside. At each distance, pots were watered with a factorial combination of treatments: high or low nitrogen, with or without sodium chloride. (2) Plants closest to the road attained highest dry weight and showed and trend towards higher total nitrogen content during the course of the experiment. These effects were most marked in plants given a low nitrogen treatment, similar to the nutrient status of roadside soils. (3) Low nitrogen plants given a salt treatment (to simulate de-icing salt) showed a significant increase in dry weight and soluble nitrogen content close to the road. This suggests that salt in roadside soils may increase the availability of nitrogen from NOx to plants. (4) The higher nitrogen content of plants close to the road correlates with more rapid increase of aphid numbers on these plants.