Effects of shading and season on growth and accumulation of major secondary metabolites in Cyclocarya paliurus

Cyclocarya paliurus is a multiple function plant, and has been traditionally used for drug formulations or ingredients of functional foods in China. Previous studies have shown that the leaves of C. paliurus contain a large number of physiological active compounds, such as flavonoids and triterpenoids, which were known to carry important physiological activity in humans. Understanding the variation patterns in secondary metabolites accumulation, and the relationship between secondary metabolism and growth along the environmental gradients can provide meaningful information for the standardized cultivation of medicinal artificial forest of C. paliurus. Shading treatment was used for studying the effects of shading treatments and sampling time on growth and accumulation of important secondary metabolites in C. paliurus from June to November. Furthermore, the relationship between secondary metabolism and growth of C. paliurus was analyzed. Our results indicated that tree height growth of C. paliurus was improved under one-layer shading, while basal diameter growth was significantly decreased under shading conditions. Accumulation of flavonoids, total triterpenoid, and cyclocarioside Ⅰ were significantly restrained by shading treatments. However, accumulation of other two individual triterpenoids cyclocaric acid B and arjunolic acid was improved by shading treatments. Under natural light condition, flavonoid contents in August and October were significant higher than other seasons, and showed a bimodal variation pattern. While, the fastigium of flavonoid accumulation in leaves of C. paliurus was delayed by shading treatment. Furthermore, under different shading conditions, the highest contents of total and individual triterpenoids were detected in September, and showed an unimodal variation pattern. A significant negative relationship between growth and accumulation of total triterpenoid and arjunolic acid was found through correlation analysis.