Effects of aqueous root leachates from dominant tree species on seed germination and seedling growth of exotic plant Rhus typhina L. in Shandong Peninsula

We conducted laboratory bioassay and pot experiments to find the difference in the allelopathic potentials of aqueous root leachates from 4-dominant tree species (Quercus acutissima Carruth., Robinia pseudoacacia L., Pinus thunbergii Parl. and Amorpha fruticosa L.) on seed germination and seedling growth of Rhus typhina L. in hills of Shandong Peninsula. All tree species root leachates inhibited the seed germination of R. typhina over the control (distilled water), except the P. thunbergii. Besides reducing the seed germination, Q. acutissima root leachates also significantly suppressed the root and shoot length of R. typhina seedlings. The pot experiments found that compared to the control group, the total biomass of R. typhina was significantly increased by low concentration (0.025 g/ml) aqueous root leachates from A. fruticosa. Our previous field investigations revealed that R. typhina rarely invades the Q. acutissima forests, possibly because of its allelopathic inhibition by Q. acutissima. The naturalized exotic species, such as A. fruticosa, share the same origin in North America with R. typhina. The R. typhina seedlings are less inhibited by A. fruticosa, possibly because of their allelopathic adaptability. The results showed that allelopathy plays role in the formation of community resistance to invasion.