Toxic effects of acetochlor, methamidophos and their combinationon nifH gene in soil
SU Zhen-cheng , ZHANG Hui-wen , LI Xin-yu , ZHANG Qin , ZHANG Cheng-gang
DOI:
Received September 11, 2006,Revised February 07, 2007, Accepted , Available online
Volume 19,2007,Pages 864-873
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Toxic e ects of two agrochemicals on nifH gene in agricultural black soil were investigated using denaturing gradient gel
electrophoresis (DGGE) and sequencing approaches in a microcosm experiment. Changes of soil nifH gene diversity and composition
were examined following the application of acetochlor, methamidophos and their combination. Acetochlor reduced the nifH gene
diversity (both in gene richness and diversity index values) and caused changes in the nifH gene composition. The e ects of acetochlor
on nifH gene were strengthened as the concentration of acetochlor increased. Cluster analysis of DGGE banding patterns showed
that nifH gene composition which had been a ected by low concentration of acetochlor (50 mg/kg) recovered firstly. Methamidophos
reduced nifH gene richness that except at 4 weeks. The medium concentration of methamidophos (150 mg/kg) caused the most apparent
changes in nifH gene diversity at the first week while the high concentration of methamidophos (250 mg/kg) produced prominent e ects
on nifH gene diversity in the following weeks. Cluster analysis showed that minimal changes of nifH gene composition were found
at 1 week and maximal changes at 4 weeks. Toxic e ects of acetochlor and methamidophos combination on nifH gene were also
apparent. Di erent nifH genes (bands) responded di erently to the impact of agrochemicals: four individual bands were eliminated by
the application of the agrochemicals, five bands became predominant by the stimulation of the agrochemicals, and four bands showed
strong resistance to the influence of the agrochemicals. Fifteen prominent bands were partially sequenced, yielding 15 di erent nifH
sequences, which were used for phylogenetic reconstructions. All sequences were a liated with the alpha- and beta-proteobacteria,
showing higher similarity to eight di erent diazotrophic genera.
