Study on the Allelopathic Effects of Camellia oleifera Rhizosphere Soil Extract on Two Medicinal Plants

Using rhizosphere soil from Camellia oleifera as the experimental material, this study explores the allelopathic effects of its extract on seed germination and seedling physiology of Isatis tinctoria and Glycyrrhiza uralensis, aiming to provide a theoretical basis for intercropping these Chinese medicinal herbs under Camellia oleifera plantations. Collect the root zone soil of Camellia oleifera, prepare 0, 25, 50, 100, and 200 g/L five concentrations of extraction solutions, respectively treat the seeds of Isatis tinctoria and Glycyrrhiza uralensis, and determine their germination rate, germination energy, root length, seedling height, SOD activity, POD activity, CAT activity, MDA content, Pro content, and chlorophyll content. Use the allelopathic effect index and allelopathic comprehensive effect index to evaluate the intensity of allelopathic effect.The results showed that at a low concentration of 25 g/L, the germination rates of Isatis tinctoria and Glycyrrhiza uralensis significantly increased, with increases of 41.30% and 20.63% respectively. The height of Isatis tinctoria seedlings increased by 10.37%, while the root length was inhibited by 17.76%. At the concentration of 25 g/L, the root length of Glycyrrhiza uralensis was significantly inhibited by 11.87%. The SOD activity of the two Chinese medicinal herbs significantly increased. The POD activity of Isatis tinctoria first increased and then decreased, while the CAT activity was all inhibited. The MDA content first decreased and then increased with the increase of concentration. The changes in Pro content of the two traditional Chinese medicinal herbs indicated their different osmotic adjustment strategies in response to allelopathic stress. The chlorophyll content increased with the increase of concentration. The allelopathic comprehensive effect index shows that for Isatis tinctoria, the SE value is 0.05 at concentrations of 25 g/L and 50 g/L, and turns to −0.02 at 100 g/L. The negative SE values of Glycyrrhiza uralensis are not significant. The allelopathic effects of Isatis tinctoria and Glycyrrhiza uralensis at all concentrations exhibit the patterns of promotion at low concentrations, inhibition or stability at high concentrations, and promotion at low concentrations, stability at high concentrations, or weak promotion, without showing strong inhibition. The allelopathic effect of the root zone soil extract of Camellia oleifera on Isatis tinctoria and Glycyrrhiza uralensis is in a concentration-dependent pattern of low promotion and high stability. Low concentrations can safely promote germination and growth, while high concentrations will have a slight inhibitory effect. This study can provide a certain basis for the theory of intercropping Isatis tinctoria and Glycyrrhiza uralensis under Camellia oleifera forest.