Structural and functional diversity of soil microbial communities as a result of combined applications of copper and mefenoxam

The effects of combined application of mefenoxam and copper on soil microbial community structure and function were investigated in laboratory microcosms over 60 days. Mineralisation of 14C-mefenoxam was followed by trapping the evolved 14CO2. The structural diversity of bacterial and fungal communities was assessed by analysing fingerprints of 16S and 18S rRNA genes and transcripts, resolved by denaturing gradient gel electrophoresis (DGGE). The functional status of the microbial community was investigated by measuring the activities of cellobiohydrolase, hemicellulase, β-glucosidase, phosphatase, aminopeptidase, chitinase and laccase. Results showed that copper application had no significant effect on the mineralisation rate of mefenoxam, although only 5.4% of the applied radioactivity was converted to 14CO2. Both copper and mefenoxam exerted selective detrimental effects on sensitive populations of fungi. In contrast, active bacterial populations were not adversely affected; instead new population structure could be observed during the exposure time. Only a few enzymes exhibited noticeable changes as a result of copper and mefenoxam treatments. Of the seven enzymes under investigation, laccase and chitinase showed an increase in their activity, which lasted till the end of the study. Thus, the study revealed a distinct effect of combined application of mefenoxam and copper both on the structural and functional diversity of microorganisms.