Soil microbial respiration and pH modulated by arbuscular mycorrhizal fungi influence the biosynthesis of health-promoting compounds in Anadenanthera colubrina (Vell.) Brenan

It is well-known that the formation of arbuscular mycorrhiza (AM) can impact edaphic properties by influencing enzymatic activities in the rhizosphere, pH and physical attributes of soil. In addition, AM can alter the biosynthesis of secondary compounds in plant species. Although, it is established that edaphic factors have significant effect on the production of secondary metabolites, yet there is no study relating AM-mediated effects on soil properties to the production of secondary metabolites. Anadenanthera colubrina (Vell.) Brenan, commonly known as cebil has high industrial and ethnobotanical relevance. The A. colubrina extract, which is of interest in herbal medicine production, is rich in flavanols, saponins and tannins. Thus, this study aimed to assess the effects of two arbuscular mycorrhizal fungi namely, Gigaspora albida and Acaulospora longula on the pharmaceutically valued compounds as well as some edaphic attributes. The ethanolic extracts of leaves of A. colubrina seedlings concentrated more flavanols, saponins, and exhibited outstanding antioxidant activity when inoculated with AMF. While, no significant effect was observed on concentration of tannins. Inoculation with G. albida resulted in 5-fold and 7-fold increase in flavanols and saponin respectively. Formation of AM resulted in higher CO2 evolution than non-inoculated A. colubrina. This indicates higher microbial activity (respiration) in the mycorhizosphere despite of the non-significant effect on soil microbial biomass due to formation of AM. Neverthless, microbial respiration in soil positively correlated with soil pH. The modulation of such parameters by AMF may explain the benefits in A. colubrina metabolism, as proven by correlation analysis. Therefore, AMF inoculation enhances the production of secondary metabolites in A. colubrina leaves by altering some rhizospheric parameters.