Heavy metal tolerance in Agropyron repens (L.) P. Bauv. populations from the Legnica copper smelter area, Lower Silesia

The copper smelter "Legnica" is one of the oldest plants in Lower Silesia. Among the few weed species spontaneously migrating to the area around the emitter there is couch grass (Agropyron repens (L.) P. Bauv.). The purpose of this study was to analyse whether the local couch grass populations, growing at various distances from the smelter, differ in tolerance to heavy metals occurring in this area. The populations were tested for tolerance to five metals (Cu, Zn, Pb, Cd, Ni) using the root elongation method. The highest tolerance to Pb developed in two populations localized nearest the smelter. Similarly, all populations of couch grass from the vicinity of the smelter show a high tolerance to copper, particularly the plants from the most contaminated site. The IT for the latter population is almost 1509r, even at the highest dose of Cu. For Zn a nearing IT as for Cu was obtained. Comparing the shape of IT curves for Cd, special emphasis is put on the fact that a fixed tolerance to cadmium occurs only in the population localized closest to the emitter. The analysis of Ni-tolerance curves, of which the content in local soil is minimal, does not confirm the thesis on possibility of development of co-tolerance in the surveyed populations. It appeared that stress conditions existing near the smelter do not inhibit seed production in couch grass, but prevent a successful course of their germination on polluted soil. The improvement of soil even by 50% (addition of unpolluted soil) does not improve the poor process of germination in couch grass growing nearest to the smelter. Of importance is the fact that the highest number of seeds germinated on their own, polluted soil. The need of metals' content for plant germination in populations most distant from the smelter is evidenced by an almost 30% reduction of germination ability of local seeds after addition of unpolluted soil. Another significant observation was the fact that, in spite of a poor germination of seeds on unpolluted soil, the further development of seedlings in populations more distant from the smelter was more intense and faster than on their native polluted soil. Thus, a certain amount of metals may stimulate the germination processes of seeds in tolerant populations, but on the other hand, it may be a hindrance to subsequent juvenile phases. During observations of development of rhizomes, taken from three polluted couch grass populations cultivated on unpolluted soil, in all of them a very slow development of rhizome buds was recorded. However, the slowest rate of appearance of buds was found in the population taken nearest the emitter which, in greenhouse conditions and at lack of metals in soil, showed a markedly poor tendency toward vegetative reproduction. All the contaminated populations display a high activity of peroxidase in leaves and roots, frequently more than twice as high than in control populations. The activity of catalase is also markedly higher, but only in two of the most contaminated populations. The recorded for the first time populations of couch grass tolerant to metals make them useful for recultivation purposes.