Improved phosphorus nutrition by arbuscular mycorrhizal symbiosis as a key factor facilitating glycyrrhizin and liquiritin accumulation in Glycyrrhiza uralensis

Background and aims Liquorice ( Glycyrrhiza uralensis Fisch.) is an important medicinal plant as it accumulates active ingredients, glycyrrhizin and liquiritin, in its roots. Arbuscular mycorrhizal (AM) symbiosis and phosphorus (P) nutrition both affect the accumulation of glycyrrhizin and liquiritin in liquorice roots and it is well known that AM symbiosis mediates P nutrition in many plant species. However, whether AM symbiosis affects the accumulation of glycyrrhizin and liquiritin in G. uralensis through P nutrition is largely unknown. Methods In order to compare the P addition and AM effects on plant performance, we carried out a controlled-environment experiment in which non-AM plants were subjected to different P addition levels compared with an AM inoculated treatment with no P addition. Plant dry weight, stomatal conductance and photosynthetic rate, root P, carbon (C) and nitrogen (N) concentrations, glycyrrhizin and liquiritin concentrations, as well as the expression of glycyrrhizin and liquiritin biosynthesis genes were measured. Results Both P addition and AM inoculation improved plant growth and photosynthesis traits. When root P concentration of non-AM plants matched that of AM plants, both plants showed similar glycyrrhizin and liquiritin concentrations, C:N ratios and biosynthesis gene expressions. Conclusions The results suggested that improved P nutrition by AM symbiosis was of primary importance for facilitating glycyrrhizin and liquiritin accumulation in G. uralensis plants. This confirmed the role of AM symbiosis improving plant P uptake in the regulation of secondary metabolite biosynthesis.