Integration of morphological, physiological and multi-omics analysis reveals the optimal planting density improving leaf yield and active compound accumulation in Ginkgo biloba

Abstract

The leaves of Ginkgo biloba contain abundant active compounds, including flavonoids and terpene lactones. Leaves of 1–5-year-old seedlings are typically harvested for ginkgo leaf extract, which is used for treatment of cardiovascular diseases, dementia, and dizziness. However, the effects of planting densities on leaf yield and leaf active compound accumulation in ginkgo are largely unknown. Here, we conducted field experiments at four planting densities (control, moderate density [MD], medium-high density [MHD] and high density [HD]) of ginkgo seedlings to investigate their leaf production and quality. As planting density increased, stem elongation was enhanced whereas root growth was inhibited. In addition, soluble sugar and starch contents were decreased in leaves with density increasing. Although the fresh and dry weights of leaves per plant were reduced, the leaf yield per unit area increased by 60.5–138.8 % in two successive years at MD-HD. Interestingly, compared with other densities, MD resulted in a higher accumulation of various bioactive secondary metabolites, including 13 flavonoids (such as homoeriodictyol, baimaside, and ladanein), ginkgolides, and bilobalide. Correspondingly, the genes encoding chalcone synthase (CHS), chalcone isomerase (CHI), and flavonol synthase (FLS), which are involved in flavonoid biosynthesis, were upregulated. However, when exceeding MD, the contents of bioactive secondary metabolites and the expression of related genes decreased dramatically. These results suggest that the MD as the optimal density could not only enhance leaf yield, but also improve active-compound accumulation in G. biloba seedling leaves, providing a practical and theoretical reference for leaf-use ginkgo plantation.