Accelerated mineralisation of atrazine in maize rhizosphere soil

The mineralisation rate of atrazine measured in soil pre-treated with this herbicide, was significantly higher in the maize rhizosphere than in bulk soil. Maize rhizosphere was also shown to significantly increase microbial biomass C as compared with bulk soil. Ribosomal intergenic spacer analysis conducted on nucleic acids extracted directly from soil samples revealed that the structure of microbial communities observed in the rhizosphere was slightly different from that of bulk soil. The quantification of the relative amount of the gene atzC, which encodes an enzyme involved in atrazine mineralisation, was carried out on soil nucleic acids by using quantitative-competitive PCR assays. It revealed that atzC was present at a higher level in the rhizosphere than in bulk soil. In addition, the amount of atzC was transiently enhanced in both rhizosphere and bulk soils following atrazine treatment. These results suggest that the stimulation of atrazine mineralisation in the maize rhizosphere depends on the abundance of atrazine-degrading communities.