Impact of imazethapyr on the microbial community structure in agricultural soils

Large amounts of imazethapyr were applied for weed control in cultivation fields in China, but their effects on the soil microbial community remains unclear. In this study, two agricultural soils, a silty loam (HS) and a loamy soil (QL), were spiked with imazethapyr (CK, 0.1, 1 and 10 mg kg(-1)) and incubated for 1, 15, 30, 60, 90 and 120 d. In addition, untreated controls received only water. The soil microbial community structures were characterized by investigating the phospholipid fatty acids (PLFA) and microbial biomass C. Soil microbial biomass C and total concentration of PLFA were variable with incubation time, which were also reduced by the addition of imazethapyr. Imazethapyr addition also decreased the ratios of GN/GP and fungi/bacteria. A larger stress level, measured as the ratio of PLFA (cyc17:0+cyc19:0)/(16:1ω7c+18:1ω7c), was found in the high concentration (1 and 10 mg kg(-1)) herbicide treatment groups. The effects of imazethapyr at the field application on soil microbial biomass and microbial community were minor. Principal component analysis (PCA) of the PLFA clearly separated the treatments and incubation times. Both soils showed different total PLFA concentrations and ratios of GN/GP and fungi/bacteria, but similar changes in the PLFA pattern upon soil treatment. The soil microbial community structure was shifted by the addition of imazethapyr, which recovered after 60d. In addition, the dissipation of imazethapyr was slow in both soils. Our results demonstrated that the addition of imazethapyr shifted the microbial community structure, but that it recovered after a period of incubation.