Mycorrhizal Effects on Active Components and Associated Gene Expressions in Leaves of Polygonum cuspidatum under P Stress

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.