Enantioselective effects of imazethapyr on Arabidopsis thaliana root exudates and rhizosphere microbes

Abstract

Imazethapyr (IM) is a chiral herbicide with two enantiomers (R-IM and S-IM). Here, we determined the enantioselective effects of IM on Arabidopsis thaliana biomass and chlorophyll content, root exudates and rhizosphere microbes after 7 days of exposure. The results suggested that 133 μg/kg R-IM enantiomer in soil slightly inhibited plant biomass but S-IM did not exert significant inhibitory effects. The rhizosphere microorganism composition was also found to have enantiomeric differences between R- and S-IM. The relative abundance of beneficial rhizosphere microbes such as Bacillus and Ramlibacter increased much more with R-IM treatment than with S-IM treatment, indicating that the rhizosphere recruited some beneficial microbes to resist the herbicide stress. The IM enantiomers exerted a significant influence on root exudates with enantioselectivity. R-IM resulted in higher levels of most amino acids, organic acids, sugars and other metabolites after 7 days of exposure; few metabolites were increased by only the S-IM treatment. The correlation analyses between compounds (sugars, amino acids and organic acid) and microbes at the genus level revealed that the number of microbes was more positively correlated with organic acids than other compounds, indicating that organic acids can attract more microbes than amino acids and sugars. Some organic acids, such as 3-hydroxybutyric acid, may be a carbon source for the beneficial microbe Ramlibacter. This study increases the understanding of the differences in IM enantiomer toxicity with respect to plant physiological activity and soil microorganisms.

Keywords: Arabidopsis thaliana; Chiral herbicides; Enantioselective; Rhizosphere microorganisms; Root exudates.