Abstract: Traditional culture-dependent method and PCR-DGGE were adopted to investigate the amount of microorganism and bacterial diversity in rhizospheric soil of transgenic Bt cotton in four provinces of  Yellow River basin at four growth stages, i.e., 30, 60, 90, and 120 days after sowing. In the same province and at the same growth stage, no significant difference was observed in the amount of microorganism in rhizospheric soils of transgenic and non-transgenic Bt cottons. Within the same province the amount of  microorganism was mainly affected by growth stage; while in different provinces, it was greatly affected by regional conditions.In the four provinces, the bacterial diversity in rhizospheric soil of transgenic Bt cotton was abundant; and in the same province and at the same growth stage, there were no significant differences in the Shannon index, evenness, and richness of bacteria in rhizospheric soils of transgenic and non-transgenic Bt cottons. In different provinces, the bacterial diversity in rhizospheric soils was dependent on regional conditions, but the difference was rather small.

Key words: cotton region of Yellow River basin, transgenic Bt cotton, soil microorganism, bacterial diversity, re-vegetation, soil biological crusts, nitrogenase activity, nitrogen fixation, hydrothermal factor.