[Toxic-effects of acetochlor, methamidophos and their combination on bacterial amount and population richness at molecular levels in agricultural black soils].

Bacterial amount and population richness in agricultural black soil under the stress of acetochlor, methamidophos and their combination were analyzed by CFU and 16S rDNA-PCR DGGE. Results showed that both of acetochlor and methamidophos had acute toxic effects on the growth of bacteria in agricultural black soil; Growth of free-living nitrogen fixing bacteria was inhibited badly by methamidophos, but stimulated greatly by acetochlor. The joint inhibitory effects of all combinations at different concentration between methamidophos and acetochlor on free-living nitrogen fixing bacteria were severer than each of their singal factors,which indicate the significant joint toxic effects between acetochlor and methamidophos on free-living nitrogen fixing bacteria in tested soil. Bacterial population diversity were decreased and the structure were changed respectively at different levels according to their concentration and combinations. Some bacterial species were diminished, but some others were accumulated under the stress of two agrochemicals and their combinations.