Objectives Cyclocarya paliurus is one of the important herbs in China. In this study, we explored the effects of elicitors on the growth, resistance, and medicinal qualities of C. paliurus to provide a theoretical basis for its efficient cultivation.
Methods A pot experiment was conducted using 2 years-old container seedlings of C. paliurus. The tested bio-elicitors were fungal elicitor (Trichoderma asperellum, F), bacterial elicitor (Bacillus amyloliquefaciens, B), and abiotic elicitor chitosan (C), and the combination of biotic and abiotic elicitors (FC and BC), and an equal amount of water control (CK). Upon harvesting of C. paliurus, the plant height and ground diameter, root, stem, and leaf biomass were measured. The leaf C, N, and P contents, superoxide dismutase (SOD), peroxidase (POD) activity, and bioactive compound contents were measured. The cultivation substrate samples were taken to analyze the pH, total N, and available N and P contents.
Results Compared with CK, the elicitors did not (P>0.05) impact the relative growth rate of seedlings but significantly increased the leaf biomass; F exhibited the highest relative growth increase, B, C, and FC had similar but higher effect than BC. The five elicitors (P<0.05) increased leaf SOD activity in the order FC>F≈C>BC>B>CK; only F and FC (P<0.05) stimulated POD activity. The elicitor treatments showed a different effect on the bioactive component and yield of C. paliurus. F demonstrated the highest content and yield of total flavonoids and total polyphenols. Additionally, treatments F, FC, B, and BC significantly increased the total triterpene content in leaves, with all treatments resulting in higher triterpene yields compared to the control. The effect on total flavonoid content was more pronounced in treatment F than in FC, and in treatment B compared to BC. Both F and C treatments significantly influenced the content of total polysaccharides, with the effect of C treatment being notably higher than that of F treatment. Cyclocaric acid B is a unique triterpenoid monomer in C. paliurus, and F and B increased its content by 77.8% and 200%, compared with CK. The application of elicitors changed the chemical properties of cultivation substrates. F and FC elicited (P<0.05) alterations in the pH of the cultivation substrate, whereas B and BC resulted in substrates with 163% and 167% higher available phosphorus and nitrogen contents, respectively, compared to CK. According to the results of the correlation analysis, the leaf N and P contents were positively correlated with the availability of soil nutrients (P<0.05). The total flavonoids in biologically active substances also showed a significant positive correlation with available soil nutrients, while the total triterpenoid was positively correlated with soil available nutrients and leaf P content (P<0.05). Furthermore, the total polyphenols exhibited a positive correlation (P<0.05) with SOD and POD activities, but negative correlation (P<0.01) with leaf N/P ratio. The total polysaccharide content was positively correlated with SOD activity (P<0.05).
Conclusions The fungal, bacterial, and chitosan elicitors enhanced the leaf yield and quality of C. paliurus efficiently. The fungal elicitor, Trichoderma asperellum, could improve the soil pH and total N, enhance the SOD and POD activity, and stimulate bioactive compound accumulation in C. paliurus leaves. The bacteria elicitor, Bacillus amyloliquefaciens, could enhance leaf enzyme activity and bioactive accumulation by improving available soil N and P, which is beneficial for leaf growth. The bacteria elicitor showed a weaker effect than the fungal elicitor in bioactive compound accumulation, while chitosan did not show a satisfactory effect except for the accumulation of leaf polysaccharides. Fungal elicitor is recommended for C. paliurus cultivation.
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