Combined Tolerance to Copper, Zinc and Lead by Populations of Agrostis Tenuis

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Abstract
The tolerance of populations of A. tenuis Sibth. growing in mining areas in Wales [UK] to the heavy metals Cu, Zn and Pb was investigated by exposing tillers to different concentrations of the metals in nutrient solutions. An index of tolerance (IT) was calculated by comparing root length with specimens grown in solutions without heavy metals. The data indicate a concomitant expression of tolerance towards the 3 metals. There is a close relationship between the IT values of the populations towards Cu, Zn and Pb, and the contents of the metals in the soils. A basic prerequisite for the development of tolerance towards toxic heavy metals is their presence in the soil, and the adaptation of the organism. Consequently, the expression of tolerance to one or more metals does not necessarily involve tolerance to other metals not present in the soil. The variability of the IT values within the populations is most probably explained by an intrinsic genetic heterogeneity in the populations, in contrast to populations growing in pastures, which demonstrate genetic homogeneity. A static gene balance is maintained in pasture populations, whereas in populations the balance is dynamic.

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