Arbuscular mycorrhizal fungal community association determines the production of flavonoids and chlorogenic acid in Acer truncatum Bunge

Arbuscular mycorrhizal (AM) fungi can affect plant secondary metabolic pathways, but how the composition and function of AM fungal communities affect the secondary metabolite content of Acer truncatum Bunge remains unknown. Ten typical A. truncatum plantations were used in southern Shaanxi province. The entropy weight method was applied to construct two grades of A. truncatum tree plantations (ordinary and superior). The interaction between AM fungi and trees in the different grades of plantations was compared. The effects of AM fungal community, soil fertility, climatic factors, and plant nutrients on the contents of flavonoids and chlorogenic acid in leaves were studied. There were no differences in the alpha and beta diversity of AM fungal associations among different grades of trees, but the hyphal colonization rate and co-occurrence network characteristics were different. There were no differences in plant height and diameter at breast height (DBH), but higher flavonoid and chlorogenic acid contents were found in the leaves of superior trees compared to ordinary trees, and this difference was attributed to variations in their AM fungal communities. For A. truncatum trees of similar growth (same height and DBH), the abundance of AM fungi was positively correlated with leaf flavonoids and chlorogenic acid contents in superior tree grade stands, but negatively correlated in ordinary tree stands. The positive correlation between leaf flavonoid content and soil fertility in superior tree grade was mediated by the beta diversity of AM fungi recruited in this environment. The relative abundance of VTX00069 and VTX00156 was positively correlated with leaf flavonoid and chlorogenic acid contents, which provides direction for the selection of AM fungi that promote flavonoids and chlorogenic acid production in A. truncatum leaves. Overall, the effect of specific AM fungal communities in the rhizosphere soil of A. truncatum on its flavonoids and chlorogenic acid contents is direct and important. This study provides new insights into enhancing the production of secondary metabolites in A. truncatum.