Effects of residual S-metolachlor in soil on the phyllosphere microbial communities of wheat (Triticum aestivum L.).

S-metolachlor (S-ME) is a widely used chiral herbicide that can cause potential ecological risks via long-term usage. In this work, we chose a model plant, wheat, as the test material to determine the effects of applying 10 mg/kg S-ME to soil on its fresh weight, chlorophyll and malondialdehyde (MDA) content, and superoxide dismutase (SOD) activity and the diversity and structural composition of the phyllosphere microorganisms after 7 and 14 days of exposure. Our work showed that this concentration of residual S-ME in soil only slightly decreased plant biomass and had little effect on lipid peroxidation, the antioxidant enzyme system and chlorophyll content. Interestingly, although the test concentration of S-ME did not exert strong inhibitory effects on the physiological activities of wheat, it decreased the diversity of phyllosphere microbial communities and changed their structure, indicating that microorganisms were more sensitive stress indicators. S-ME reduced the colonization by some beneficial bacteria related to plant nitrogen fixation among the phyllosphere microorganisms, which influenced the growth and yield of wheat because these bacteria contribute to plant fitness. In addition, S-ME affected the association between the host and the composition of the phyllosphere microbial communities under different growth conditions. Our work provides insights into the ecological implications of the effects of herbicides on the phyllosphere microbiome.