Polygonum cuspidatum Sieb. et Zucc. is a major raw material for the extraction of drugs such as resveratrol, while the over-exploitation of P. cuspidatum decreases the yield and drug components. The purpose of this study was to analyze the effect of inoculation with root endophytic fungi Funneliformis mosseae and Piriformospora indica singly or in combination in biomass production, physiological activities (e.g., chlorophyll, soluble protein, and gas exchange) and main medicinal ingredients of P. cuspidatum, accompanied by the expression levels of associated genes in resveratrol biosynthesis. Single and co-inoculation with P. indica significantly improved shoot and root biomass production, and single and co-inoculation with F. mosseae and P. indica, especially single P. indica, significantly promoted leaf chlorophyll and soluble-protein concentrations and improved leaf gas exchange, including photosynthetic rate, transpiration rate, stomatal conductance, and intercellular CO₂ concentration. The application of endophytic fungi increased resveratrol and polydatin concentrations, while it affected chrysophanol, emodin, and physcion concentrations in a complex manner. In addition, F. mosseae inoculation and co-inoculation induced the expression of PcCRS1, PcRS11, PcRS, and PcSTS, and only single F. mosseae and P. indica inoculation up-regulated the expression of PcCHS1 and PcCHS2. It was concluded that endophytic fungi accelerated biomass production, leaf physiological activity, and resveratrol accumulation in P. cuspidatum, which was associated with the up-regulation of related gene expression in resveratrol biosynthesis.

Arbuscular mycorrhizal fungi (AMF) participate in the process of plant secondary metabolism and thus affect the production of secondary metabolites. However, it is not clear whether and how AMF affect the growth and secondary metabolites of Polygonum cuspidatum, a medicinal plant rich in resveratrol and polygonin, under different phosphorus (P) levels. This study was performed to analyze the effects of Glomus mosseae on the growth, leaf gas exchange, P concentration, active ingredient concentrations, and expressions of associated genes of P. cuspidatum under P-deficient (0 mol/L P) and P-sufficient (0.2 mol/L P) conditions. The root mycorrhizal colonization rate of inoculated plants was 62.53–73.18%. G. mosseae improved shoot and root biomass as well as leaf P levels to some extent, but the improvement was more prominent under P-sufficient than P-deficient conditions. The fungal colonization also significantly increased leaf photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO₂ concentration, which was more prominent under P-deficient rather than P-sufficient conditions. P addition promoted the concentration of active medicinal components in leaves, especially in uninoculated plants. G. mosseae distinctly raised leaf chrysophanol, emodin, polydatin, and resveratrol concentrations, which was more prominent under P-deficient conditions. However, physcion was raised by G. mosseae only under P-sufficient conditions. AMF and P addition up-regulated expressions of PcCRS1, along with the up-regulation of PcRS11 by P addition and PcRS11 and PcSTS by AMF under P-sufficient conditions. It is concluded that an adequate P fertilizer and AMF facilitate the production of active medicinal components in P. cuspidatum, associated with expressions of associated genes such as PcCRS1.