Abstract: The water extract of the roots of two poplar clones,Nanlin 95 and NL-80351,was used to treat the seeds of wheat,rape,cabbage,and cotton.The results showed that the water extract could affect seed germination,seedling height and root length of wheat,rape and cabbage,especially at a high concentration.The affected intensity to wheat was strongest,and to rape was in the medial.The water extract promoted the seed germination,seedling height,and root length of cotton significantly.Regarding to the suppression to seed germination,seedling height,and root length of wheat and rape,and to the promotion to seed germination and seedling height of cotton,the water extract of Nanlin 95 clone was stronger than that of NL-80351 clone.But the promotion to root length of cotton was on the contrary.The effects to cabbage were a little different to those of another.As to the suppression to seed germination and root length,the water extract of Nanlin 95 clone was stronger than that of NL-80351 clone.And to seedling height,a contrary conclusion was drawn.The water extract of Nanlin 95 clone suppressed it,while that of NL-80351 clone promoted it.The conclusions can be referred to the species selection of agroforestry systems.