Mycorrhizal Fungi Synergistically Promote the Growth and Secondary Metabolism of Cyclocarya paliurus

Cyclocarya paliurus has traditionally been used as medicine or a nutraceutical food. This study aims at investigating whether the growth and secondary metabolism of C. paliurus could be simultaneously promoted by inoculating with mycorrhizal fungi, and if so, to uncover the underlying regulatory mechanism. A mycorrhizal microbial inoculum, consisting of the superficial layer fine roots and rhizosphere soil collected from the natural forest of C. paliurus, was used to infect aseptic seedlings of C. paliurus. Roots of aseptic seedlings were successfully infected by mycorrhizal fungi with a 59.7% colonization rate. For mycorrhizal seedlings of C. paliurus, the induced endogenous auxin, net photosynthetic rate, nitrogen absorption, and growth-related genes resulted in a significantly higher growth and biomass accumulation. In addition, a systemic defense response was observed in response to mycorrhizal fungal colonization, such that jasmonic acid biosynthesis and signaling were induced and the biosynthesis of secondary metabolites and antioxidant systems were up-regulated. The improved growth and accumulation of secondary metabolites ultimately facilitated the yield of health-promoting substrates per plant. Overall, mycorrhizal fungal colonization had a significant positive effect both on growth and production of secondary metabolites in C. paliurus. The results can provide the basis for overcoming the limitation of soil nutrient regulation in cultivation practice and offering a simpler alternative to improve the quality of medicinal plants.