Effects of the herbicide mesotrione on soil enzyme activity and microbial communities.

Mesotrione (2-[4-(methylsulfonyl)-2-nithobenzoyl]-1, 3-cyclohexanedione) is a selective triketone herbicide that has been widely used in corn production for the past 15 years. However, its potential for risk to soil ecosystems is poorly documented. The present study investigated the soil enzyme activity and soil microbial community responses to a 20 days' mesotrione exposure at doses of 0.1, 1.0 and 5.0 mg/kg. On days 2, 5, 10 and 20, activities of soil β-glucosidase, urease and acid phosphatase, soil microbe abundances, soil microbial community structure and abundance of the AOA-amoA and AOB-amoA genes were measured. Results showed that activities of urease and acid phosphatase were relatively stable, with no difference found between the mesotrione-treated group and control at the end of exposure. But β-glucosidase activity was reduced in the 5.0 mg/kg mesotrione treatment. In the 1.0 and 5.0 mg/kg mesotrione-treated soil, abundance of bacteria, fungi and actinomycetes all were reduced. In the 0.1 mg/kg mesotrione-treated soil, only fungi abundance was reduced by the end of the exposure. The analysis of terminal restriction fragment length polymorphism (T-RFLP) revealed soil microbial community structure could be affected by mesotrione at all experimental doses, and microbial diversity declined slightly after mesotrione exposure. Abundance of AOA-amoA and AOB-amoA genes were reduced markedly in 1.0 and 5.0 mg/kg mesotrione-treated soil. The present study suggests that mesotrione at higher doses might induce negative impacts on soil microbes, a finding which merits additional research and which should be accounted for when application of this herbicide is considered.