Clomazone influence soil microbial community and soil nitrogen cycling.

We designed an indoor mesocosm experiment to investigate the long-term effects of exposure to clomazone, a widely used herbicide, on soil microbial communities and their nitrogen (N) cycling functions. Clomazone was applied to two typical soils from China at three concentrations: 0.8 (the recommended dosage), 8 and 80 mg kg soil dry weight, and the mix was incubated for 90 days. Samples were removed periodically for assay with several techniques. The half-lives of clomazone in this experiment were 11-126 d. Results were significant only for the highest clomazone concentration. Next-generation sequencing of the 16S and 18S rDNA genes revealed that bacterial diversity significantly decreased whereas fungal abundance increased after day 60 but with no detectable effect on the microbial community. Hierarchical cluster and principal coordinates analysis revealed that the bacterial community structure was negatively impacted. Linear discriminant analysis of effect size identified Sphingomonas and Arthrobacter as the predominant bacterial species. Finally, we measured soil NH and NO concentrations and used real-time PCR to analyze the abundance of the N-cycling genes, nifH and amoA. In the first 30 days, the NO-N content and the number of ammonia-oxidizing bacteria increased. N-fixing bacteria were inhibited after 60 days, but the NH-N concentration remained unchanged and was likely provided by ammoniation.