The effects of zinc contamination from electricity pylons: evolution in a replicated situation

Most electricity pylons are zinc coated. It might be possible for this to cause zinc contamination of soil beneath the pylons sufficient to impose selective forces by which zinc-tolerant populations would develop in a replicated manner. An investigation of Agrostis capillaris L. populations sampled under a series of pylons in North Wales shows that: (1) Zinc concentrations are considerably greater in soils beneath pylons, particularly adjacent to pylon legs. (2) Soils sampled under different pylons had mean zinc concentrations varying from 1250 ± 200 to 6500 ± 4000 μ g g-1as total, and from 570 ± 188 to 3000 ± 2000 μ g g-1as acetic acid extractable. In control soils, comparable values were from 170 ± 35 to 320 ± 90 μ g g-1total zinc, and 70 ± 10 to 140 ± 30 μ g g-1acetic acid-extractable zinc. (3) Zinc toxicity is found in such soils causing significant reduction in plant dry weight and tiller production of normal material of A. capillaris. (4) The pattern of root growth response to increasing zinc concentration in solution culture of samples of adult plants collected from beneath pylons differed significantly. (5) Some individuals had zinc tolerance equivalent to that of zinc mine plants; others had low but measurable tolerance; others differed little from plants from uncontaminated control sites. These results clearly show that evolution of zinc tolerance has occurred rapidly, since the pylons sampled were all less than 30 years old, but the outcome is different under different pylons, almost certainly because of differing genetic constitutions of different founding populations.