Effects of Understory Planting Patterns on the Accumulation of Secondary Metabolites in Panax quinquefolius L. and Their Possible Mechanisms.

Understory planting patterns significantly influence the accumulation of secondary metabolites in the roots of Panax quinquefolius L. However, research on the mechanisms underlying these effects remains limited. Two treatments, field planting and understory planting, were established in this study. Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) was utilized to determine the differences in root secondary metabolites of P. quinquefolius across these two planting modes. Additionally, the differences in the bacterial and fungal compositions of rhizosphere soils were analyzed using 16S rRNA and ITS sequencing. Untargeted metabolomics was utilized to evaluate variations in soil metabolites within the rhizosphere. Observations of rhizosphere arbuscular mycorrhizal fungi (AMF) colonization were conducted with a compound light microscope. The relationships between root secondary metabolites, rhizosphere microorganisms, and differential soil metabolites were assessed using Procrustes Analysis and Mantel-test correlation analysis. The results indicated that the content of ginsenosides of the understory planting pattern P. quinquefolius increased. Additionally, there was an observed increase in rhizosphere microbial diversity and community complexity, as well as enhanced arbuscular mycorrhizal fungi (AMF) colonization. The relative abundance of microorganisms showed significant correlations with the content of plant secondary metabolites. Notably, the contents of rhizosphere soil metabolites columbin and glycyl-L-leucine increased, while ginsenosides and rutin levels decreased, exhibiting significant correlations with ginsenoside content in the roots of P. quinquefolius. This paper explores the mechanisms underlying the quality formation of P. quinquefolius in understory planting, focusing on rhizosphere microecology and soil metabolism, and establishes a foundation for developing ecological understory planting practices.