Effects Of S-metolachlor On Wheat Seedlings(Triticum Aestivum L.)root Exudates And Symbiotic Microorganisms

Pesticides play an important role in controlling plant diseases and insect pests,promoting crop quality and yield,are one of the most effective tools in agricultural production.With the development of intensive agriculture,pesticides application amount has increased rapidly.The amount of herbicides accounts for more than 40% of the total use of pesticides.The large-scale application of herbicides has caused serious environmental problems.As the second “genome” of plants,plant symbiotic microorganisms are inevitably affected.This study takes the plant symbiotic microbiome as the research object and explores the effects of typical herbicides on the plant symbiotic microbiome in the environment,which hope to in-depth assessment of the environmental risks of herbicides and to deepen the understanding of the relationship between plants and symbiotic microbiome.S-metolachlor(S-ME)is a typical chloroacetanilide herbicides,its herbicidal effect is 1.4-1.6 times higher than that of metolachlor,and thus recommended to use.In this study,wheat was used as a model plant,16 S r RNA gene sequencing and metabolomics were used to study the change of wheat seedlings physiological,the metabolic response of wheat root exudates and the symbiotic microorganisms of wheat.The study results showed that S-ME significantly inhibited on the shoot fresh weight and root node number of wheat seedlings;Treatment of S-ME can activate superoxide dismutase and peroxidase in wheat seedling tissue;and significantly increased oxidation substances and products such as malondialdehyde and hydrogen peroxide,which cause oxidative damage to wheat.The wheat seedling root exudates are also affected by S-ME: the secretion of organic acids(e.g.caproic acid)and some compounds with antioxidant properties(e.g.carbazole,2-hydroxyquinoline)was induced.16 S r RNA analysis indicated that S-ME reduced the richness of rhizosphere microorganism community but recruited beneficial Rhizobiaceae,Burkholderiaceae and etc into the wheat rhizosphere environment.The spearman correlation analysis showed that the enrichment of Rhizobiaceae and Burkholderaceae in wheat rhizosphere environment were positively correlated with the hexanoic acid and bate-alanine secreted by wheat roots,respectively,suggesting that beneficial microorganisms may be attracted by organic acids.Analysis of phyllosphere microbial communities showed that the diversity of phyllosphere microbial community was decreased by S-ME and the relative abundance of beneficial microorganisms Rhizobiaceae and Burkholderiaceae were reduced,especially Burkholderiaceae.The study results demonstrated that S-ME had an obvious phytotoxicity on wheat growth,and that S-ME significantly affected the secretion of wheat seedling root exudates.Additionally,S-ME significantly changed the rhizosphere microbial community of wheat and recruited beneficial microorganisms in the rhizosphere.The enrichment of beneficial microorganisms in the rhizosphere could be the result of root exudates regulation.Our results also demonstrated that S-ME was not conductive to the colonization of beneficial microorganisms in the phyllosphere and decreased the community diversity of phyllosphere microorganisms.Overall,this study is instructive for exploring the interaction between herbicides and plant microbiome,helping us understand the connection between plants and symbiotic microorganisms,and provides a more comprehensive assessment of the environmental risks of herbicides.