Global metabolic changes induced by arbuscular mycorrhizal fungi in oregano plants grown under ambient and elevated levels of atmospheric CO.

Symbiotic plant-microorganisms interaction is a promising approach to avoid the environmental hazards of synthetic fertilizers and pesticides. Among these, arbuscular mycorrhizal fungi (AMF) are known to improve the growth and quality of many plant species; however the detailed metabolic mechanisms behind such beneficial effects are far from complete. Further, elevated levels of atmospheric CO (eCO) could affect such AMF-plant association. Herein, we have investigated the individual and synchronous impact of AMF and eCO (620 ppm) on nutrient uptake, growth, photosynthesis, respiration, and levels of primary and secondary metabolites in oregano (Oreganum vulgare), an economically important herbal plant. Enhanced AMF colonization rate and a better mycelial growth were observed in roots of oregano grown under eCO. Both AMF and eCO treatments significantly enhanced the growth and photosynthesis of oregano plants, however much improvements were observed by their synchronous application. eCO further increased the AMF-induced dark respiration and accumulation of macro and microelements. Hierarchical clustering analysis of individual primary and secondary metabolites revealed a metabolite-dependent response toward AMF and eCO. The synchronous application of AMF and eCO resulted in promoted accumulation of the majority of the detected sugars, organic acids, amino acids, unsaturated fatty acids, phenolic acids and flavonoids, as compared with the sole treatments. Moreover, AMF and eCO acted synergistically in improving the antioxidant capacity and anti-lipid peroxidation activity of oregano. Therefore, this study suggests that AMF treatment induces a global metabolic change in oregano, the effect that is strengthened under eCO.