Effects of S-metolachlor on wheat (Triticum aestivum L.) seedling root exudates and the rhizosphere microbiome.

S-metolachlor (S-ME) is a common chloroacetanilide herbicide. Here, we investigated the effects of S-ME on wheat seedling growth and explored via metabolomics the driver through which S-ME changes the rhizosphere microbiome. The results indicated that 4 mg/kg S-ME had a strong inhibitory effect on plant growth by inducing hydrogen peroxide (H2O2) levels. The richness of the rhizosphere microbiome markedly decreased after S-ME treatment, although the abundance of some potential beneficial rhizobacteria, such as Rhizobiaceae and Burkholderiaceae, increased suggesting that plants recruited potential beneficial microorganisms to resist S-ME-induced stress. Spearman correlation analysis revealed that Rhizobiaceae and Burkholderiaceae were positively correlated with organic acids secreted by plants after S-ME treatment, implying that potential beneficial microorganisms may be attracted mainly by organic acids. Our results demonstrated the phytotoxicity of S-ME on crop growth and indicated both that S-ME could influence rhizosphere microorganism abundance and that recruitment of potential beneficial microorganisms could be the result of root exudate regulation.