Allelopathic effects of walnut leaves leachate on seed germination, seedling growth of medicinal plants

To identify the tolerant understory species of medicinal plants for intercropping with walnut, the allelopathic effects of walnut (Juglans regia L) leaves leachate (0, 0.25%, 0.5%, 2.5%, 5%) were investigated on the seed germination, seedling growth and physiology of 4 medicinal plants [Isatis tinctoria L., Atractylodes macrocephal Koidz., Polygala tenuifolia Willd. and Salvia miltiorrhiza Bge.]. The aqueous leachate of walnut leaves exerted different allelopathic effects on the test medicinal plants. All aqueous leachate significantly inhibited the seed germination and seedling growth of S. miltiorrhiza., however, lower concentration (0.25%) improved the seed germination and seedlings growth of I. tinctoria., A. macrocephala and P tenuifolia.. All aqueous leachate had less effects on the fresh weight of P. tenuifolia Willd.. The higher leachate concentration (5%) was inhibitory to all studied parameters. Root length was more sensitive to leachate than shoot length. Among the physiological variables measured, net photosynthesis rate was most sensitive to leachate. The inhibitory/stimulatory effects of walnut leaves leachate differed with receptor plants.