Abstract:Using petri dish bioassay, the allelopathic effects of roots, branches, leaves, seeds extracts and volatile oil of Platycladus orientalis were studied on the seed germination and seedling growth of Pinus tabulaeformis. The results showed that P.orientalis had allelochemicals, and all extracts had allelopathic effects on the seed gremination and seedling growth. Furthermore, the promotion effect of extracts on seedling growth at low concentration (2 mg·mL-1) was stronger than the inhibition at high concentration (30 mg·mL-1). The aqueous extracts of roots promoted the seedling root and shoot fresh weight growth by 79.78% and 376.60%, respectively at 2 mg·mL-1 concentration; The aqueous extracts of leaves exhibited the strongest promotion effect on the growth of seedlings by 102.41%; The aqueous extracts of branches exhibited the strongest promotion effect on the seed germination by 65.63%. On the contrary, all extracts had no obviously allelopathic effects at high concentration (30 mg·mL-1) except the roots and branches aqueous extracts on the seed germination (87.50%) and the growth of seedlings fresh weight (85.11%). The volatile oil of P.orientalis had significant promotion effect on the seed germination by 70.37%. It indicated that mixed planting P.orientalis and P.tabulaeformis in proper proportion and pattern could have promotion effect on the growth of P.tabulaeformis and forest production.