Heavy metals in soils, vegetation development and heavy metal tolerance in plant populations from metalliferous areas

摘要

The development of vegetation (mainly the Violetum calaminariae Schwick) in heavy metal-contaminated areas depends on the metals mobility in soils and on metal availability for plants. Moreover, the ability of plant populations to evolve metal tolerance is one of the most important characters which determines the structure, density and development of the vegetation in such areas. In this work, metal mobility in soils and availability to plants in both calcareous and noncalcareous situations were investigated in relation to the development of genetic heavy metal tolerance in plant populations. In soils, exchangeable metals amounts are linearly related to total amounts. Availability of metals for plants depends on soil pH and on organic matter contents. High calcium content in soils reduced lead toxicity more than zinc toxicity and generally reduced metal uptake but some exceptions were found. The structure and the density of the vegetation colonizing calcareous and non-calcareous places is related to the interaction between lead, zinc and exchangeable non-toxic cations. A relationship between exchangeable Pb++/Ca++ in soils and the lead tolerance level of plant populations was found. The relation between exchangeable Zn++/Ca++ and zinc tolerance level was not satisfactory.