The influence of Rhizophagus irregularis arbuscular mycorrhizal fungus on Echinacea purpurea root biomass and bioactive compounds

Echinacea purpurea is a widely used medicinal plant valued for its bioactive constituents; however, cultivation presents several challenges (poor and imbalanced germination, slow initial development). Arbuscular mycorrhizal fungi (AMF), especially Rhizophagus irregularis, are known to influence plant growth and metabolite accumulation, yet limited multi-year field data exist. This is the first study that evaluates the effect of R. irregularis inoculation on root biomass, phenolic acid content, essential oil yield and its composition in two-year-old E. purpurea under greenhouse (four substrate types) and open-field conditions. Chicoric acid was the predominant phenolic in all samples. Significant substrate- and environment-dependent effects were found for other compounds: AMF-treated plants showed increased caftaric (2.87-fold) and caffeic (2.15-fold) acid levels on sterile peat and elevated cynarin (2.13-fold) under field conditions, but decreased caffeic acid (3.39-fold) and echinacoside (1.98-fold) on gleyic calcaric Fluvisol. On stagnic Luvisol and gleyic calcaric Fluvisol, treated plants showed a higher proportion of oxygenated sesquiterpenes in oil composition, while controls contained fatty acids along with sesquiterpene hydrocarbons. A negative correlation was found between AMF colonization rate and both phenolic content and essential oil yield under open-field conditions. The results suggest that the effects of R. irregularis are strongly influenced by substrate type and environmental conditions, indicating the need for further research.