Regulatory Effects of Two Ionic Liquids ([Omim]Br, [Opy]Br) on the Growth and Root Microecology of Maize Seedlings

Accumulation of ionic liquids (ILs) in soil may alter its physicochemical and biological properties. However, the current understanding of their effects on the rhizosphere microenvironment of crop plants remains limited. We examined the effects of two ILs—[Opy]Br and [Omim]Br—which differ in cation structure but share the bromide anion, on maize rhizosphere microbial communities and metabolites at a concentration of 0.6 g/kg soil. Exposure to [Opy]Br and [Omim]Br significantly impaired maize seedling development, with [Opy]Br inducing more severe growth suppression. These phytotoxic effects were also reflected in changes in rhizosphere soil properties. In bacterial communities, [Omim]Br more strongly inhibited membrane transport (e.g., ATP-binding cassette transporters), lipid synthesis, and carbon metabolism, thereby impairing bacterial nutrient uptake and energy metabolism. In fungal communities, saprophytic fungi were activated under both treatments, accelerating organic matter decomposition, whereas pathogens were suppressed, particularly under [Omim]Br treatment. Metabolomic analysis revealed widespread accumulation of amino acids in maize roots following exposure to both ILs, accompanied by significant depletion of the antioxidant glutathione. Carbohydrate metabolism was broadly suppressed, with [Omim]Br exerting a more pronounced inhibitory effect. Hormone levels were generally reduced, with [Opy]Br causing more severe depletion. Overall, both ILs induced oxidative stress, hormonal disruption, and metabolic imbalance in maize. This study provides a reference for evaluating the risks and regulatory potential of ILs in agricultural environments.