LEAD-INDUCED CHANGES OF RHIZOSPHERIC BACTERIUM POPULATIONS IN DIFFERENT ROOT ZONES

The aim of the experiments was to determine the influence of lead on t he rhizospheric bacterial populations of the selected root zones of th e bean plants (Phaseolus sp.) growing in the soil treated with PbCl2 ( 2,000 and 4,000 ppm Pb2+). In the investigations estimated: the total number of bacteria, the number of denitrifiers and aninionifiers, and the number of Pseudomonas and Arthrobacter bacteria inhabiting the rhi zosphere and the non-rhizospheric soil. Moreover, the lead accumulatio n in plant organs was estimated and the lead-induced reduction of thei r length was measured. It was noted that the greater the dose of lead was, the greater was its influence on the number of all tested populat ions occurring in the rhizosphere and non-rhizospheric soil. We also f ound out that the rhizosphere of the root elongation zone lacked the r hizospheric effect. These results indicated that lead is accumulated m ore intensely in the root elongation zone, and its toxic effect is hig her here.