Effects of Five Herbicides on Bacterial Communities in Upland Red Soils

Herbicides are widely used to control weeds in cropland. Meanwhile, they may have consequences on non-target organisms in soil. However, the ecological effects of different types of herbicides are still poorly understood and less compared. This study explored the impacts of herbicides on bacterial communities in differentially fertilized upland red soil, which is the dominant soil type in southern China. Five commonly used herbicides (pre-emergence: acetochlor, butralin, imazameth; post-emergence: fluoroglycofen-ethyl and quizalofop-p-ethyl) were added to soil microcosms. The soil bacterial communities were analyzed by high-throughput sequencing of the 16S rRNA genes. The results show varied effects associated with individual herbicides on the bacterial communities in these upland red soils. The responses of soil bacteria to acetochlor, butralin and imazameth were similar, which altered the diversity and composition of bacterial communities, leading to the relative enrichment of Ktedonobacteraceae of Chloroflexi, as well as the increase in negative correlations in the co-occurrence network. In contrast, fluoroglycofen-ethyl and quizalofop-p-ethyl were less influential. These differences may be related to the activity difference between pre-emergence and post-emergence herbicides. Exposure time, as well as soil properties caused by long-term application of either chemical fertilizers (CF) or combined mineral and organic fertilizers (OM), were also identified as important factors influencing the ecological effects of herbicides such as butralin, quizalofop-p-ethyl, and imazameth. These findings reveal the complexity of the soil ecological effects of different herbicides, and will provide a scientific basis for the safe application of herbicides in upland red soil.