The Effects of Fig Tree (Ficus carica L.) Leaf Aqueous Extract on Seed Germination and Seedling Growth of Three Medicinal Plants

Fig tree cultivation land resources are not fully utilized and introducing them into sustainable medicinal agroforestry systems can effectively achieve resource protection and reuse. Laboratory and pot experiments were applied to study the allelopathic effects of fig tree (Ficus carica L.) leaf aqueous extract at five mass concentrations of 8.3, 10.0, 12.5, 16.7, and 25.0 g/L on the morphological and physiological indexes of mint (Mentha haplocalyx Briq.), dandelion (Taraxacum mongolicum Hand.-Mazz.), and woad (Isatis indigotica Fort.). The results showed that mint had the best seed germination rate. The leaf aqueous extract at lower concentrations had a strong promoting effect on the biomass and photosynthetic parameters of mint, dandelion, and woad. With the increase in leaf aqueous extract concentration, the superoxide dismutase, peroxidase, and catalase activity of mint, dandelion, and woad increased initially and then decreased, but the malondialdehyde content increased. The synthetic allelopathic indexes of the three medicinal plants were in the following order: mint > woad > dandelion. Both the low and medium concentration extracts (8.3 g/L–12.5 g/L) showed an obvious promoting effect, while high concentrations exhibited distinct inhibiting effects. In conclusion, mint is the most suitable medicinal plant to be interplanted with fig trees for introduction into medicinal agroforestry systems.