Impact of herbicide 2, 4-dichlorophenoxyacetic acid butyl ester on soil nitrogen-transforming bacterial populations in two soils

Abstract

Herbicides applied to the field affect the soil microbial community. Here, we evaluated the impact of the herbicide 2,4-dichlorophenoxyacetic acid butyl ester (2, 4-Dbe) on the microbial community and nitrogen-transforming bacterial populations at three doses of 0, 5 (field application rate) and 50 mg (ten-fold field rate) active ingredient (a.i.) kg-1 dry soil applied to Oxisol and Fluvo-aquic soils in the laboratory, respectively. After addition of 2, 4-Dbe, the populations of aerobic bacteria and actinomycete significantly depressed in the Oxisol soil (pH 5.9), while promoted in the Fluvo-aquic soil (pH 8.3). An increasing dose of 2, 4-Dbe combined with much less fungal populations in both soils (p < 0.05). Application of 5 mg a.i. 2, 4-Dbe significantly stimulated ammonifiers, and had no influence on nitroso-bacteria and denitrifying bacteria; 50 mg a.i. 2, 4-Dbe inhibited all of them (p < 0.05). Both doses of 2, 4-Dbe inhibited autotrophic nitrifying bacteria, but stimulated heterotrophic nitrifying bacteria in both soils (p < 0.05). These results revealed that the sensitivity of different microbial species to 2, 4-Dbe differed significantly, and the impacts were also associated with herbicide application rates and soil types. Fungi and autotrophic nitrifying bacteria are more sensitive, and heterotrophic nitrifying bacteria are insensitive to 2, 4-Dbe toxicity.