Contribution of arbuscular mycorrhizal fungi in attenuation of heavy metal impact on Calendula officinalis development

The mycorrhizal fungi community is a significant soil rhizosphere component that benefits plant nutrition and improve plant tolerance to abiotic stresses. The present research compared the influence of three mycorrhizal strains over pot marigold (Calendula officinalis L.) development and their contribution to promoting the valuable secondary metabolites accumulation in the condition of heavy metal (Cd and Pb) pollution. Two Claroideoglomus claroideum isolates (from industrially and naturally enriched metal-contaminated sites) and Funneliformis mosseae (derived from a soil with a high concentration of various metals) were studied. The mycorrhizal status and acid phosphatase activity were best exposed in the roots associated with C. claroideum (from native metalliferous sites) and corresponded with the highest total phenols and flavonoids concentrations. Neither Pb nor Cd was detected in the marigold flowers (Calendula flos drug) following targeted mycorrhizal treatment. The higher Cd and Pb levels in non-mycorrhizal plants lead to the lowest flower weight, but in the aerial plant parts, we found a slight distinction. The tested strains stimulated the accumulation of important secondary metabolites (total phenols, flavonoids, carotenoids) in pot marigold flowers and, therefore, enhanced the antioxidant capacity. The carotenoid profile of mycorrhizal plants performed notable differences between the primarily defined constituents (lutein, lycopene, β-carotene). The highest β-carotene values (respectively vitamin A) and lycopene were found in pot marigold—F. mosseae association. The findings are essential to obtain the optimum benefits of mycorrhizal association in unfavorable conditions concerning pot marigold bioactive compounds synthesis.