Phytotoxicity and bioherbicidal potential of sweet flag (Acorus calamus L.) essential oil on Fabaceae and Brassicaceae species

• Phytotoxic activities of sweet flag essential oil make it a potent solution for weed management. • In half-inhibitory concentration essential oil increases ROS generation and modulates antioxidative system response. • Essential oil triggers a species- and family-specific response of plant metabolism. • The oil alters the fatty acid composition and increases their peroxidation in roots. Given the growing need to phase out chemical pesticides, plant-derived compounds are being investigated as eco-friendly alternatives. Sweet flag ( Acorus calamus ) essential oil (SEO), traditionally used in Chinese medicine, remains underexplored in terms of its phytotoxic properties and agricultural potential. This study evaluated the phytotoxic effects of 24-hour seedling incubation with emulsified SEO on primary root growth, cell viability, oxidative stress, overall metabolism (protein and sugar levels, fatty acid profile), and lipid peroxidation in Fabaceae ( Vicia faba, Lupinus luteus ) and Brassicaceae ( Brassica napus, Arabidopsis thaliana ), focusing on interfamily and interspecies selectivity. Half-maximal inhibitory concentrations (IC₅₀) were determined as follows: 0.03 % for V. faba , 0.025 % for L. luteus , 0.01 % for B. napus , and 0.005 % for A. thaliana . Despite similar stress intensities defined by IC₅₀, SEO reduced root biomass in a species-dependent manner. Oxidative stress was confirmed by increased reactive oxygen species (ROS), with the highest H₂O₂ accumulation observed in Fabaceae, reaching 267 % of control in V. faba and 340 % in L. luteus , but staying below 200 % in Brassicaceae. Nonetheless, Fabaceae activated more efficient antioxidant defenses, as reflected by species-specific modulation of ascorbate, glutathione, carotenoids, and the activities of SOD, APX, GR, and CAT. In contrast, Brassicaceae experienced stronger metabolic disturbances, evidenced by enhanced heat emission (isothermal calorimetry), increased lipid peroxidation, membrane damage, elevated electrolyte leakage, and a greater decline in cell viability. These results underscore the species-specific responses to SEO and highlight its selective phytotoxicity, supporting its potential as a sustainable bioherbicide that effectively targets Brassicaceae weeds while preserving Fabaceae crops.