| Walnut ( Juglans regia L. ) is a kind of allelopathic tree. Choosing an appropriate associate specie is very important for walnut comprehensive management patterns. Scutellaria baicalensis Georgi is one of the Third-grade State wild medicinal plants. It has been in lack because of the serious damage and the improperate cultivation systems. In nowadays, Walnut has been successfully cultivated with many kinds of medicinal plants , and the pattern of Walnut and Baicalensis seems to be the best one. In this paper, we designed a pot experiment, used dynamic head-space and GC-MS methods, and probed into the effects of the Walnut allelochemicals on Baicalensis through volatile gas, eluviation and root exudates. Through this experiment, we also got several important conclusions:(1) The components of volatiles from Walnut were varied with seasons. Firstly, according to the number of volatiles, the order from high to low was: November > May > August. Secondly, based on the contents of terpenoid volatiles, the order from high to low was: August > May > November. The results showed that there were more terpenoids in August than May and November. In other words, walnut might have stronger potential effects on other plants nearby in August. The result indicated that the main component of volatile gas was monoterpene. It was different from the results tested by former researchers.(2) Limonene was the main terpenoid in volatile gas. It enhanced seed germination of Baicalensis when concentration was low and it inhibited the same action when concentration was high. With the effect of Limonene, the mean time of germination was longer than that of control. And the higher the concentration, the stronger the inhibition.(3) The aqueous extract from Walnut leaves and roots had effects on Baicalensis seedlings. First, the aqueous extract with low concentration greatly promoted the seedlings' growth, and the promotion effect increased gradually with the increasing concentration. But, this kind of effect decreased when the concentration reached a certain point, and also, it changed into inhibiting effect if the concentration kept increasing . Second, the aqueous extract had positive effects on height, root length, biomass, the photosynthetic rate, transpiration rate, stomatal conductance, chlorophyll content, fluorescence characteristics and nutrient content of seedlings when the concentration was low, and it brought negative effects when the concentration was high. The initial aqueous extract concentration which resulted in inhibition effect from root was lower than that from leaf. Third, With low concentration, leaf and root aqueous extract deflnatiely improved the stomatic resistance, protecting enzyme activities and MDA contents with high concentration and it blocked them with low concentration.(4) Different concentrations of juglone had different kinds of inhibition influence on the Baicalensis seed germination . Juglone concentration at any level had inhibited effects on effective germination percentage and germination potential. This inhibition effect got up when the concentration became higher. At the same time, it cut down the mean days of seeds germination with low concentration, and it extended the time at different level with high concentration. The higher the concentration, the longer the time is.(5) The effect on Baicalensis seedlings' growth engendered by different juglone concentration was related to cultivated density of Baicalensis seedlings. It had inhibiting effect with low cultivated density and this kind of effect was enhanced when the concentration of juglone got up. Similarly, It had facilitate effection with high cultivated density and this kind of effection was enhanced when the concentration of juglone got down. Besides, with the same concentration, the inhibiting effect weakens gradually when the cultivated desity becomes higher and if the cultivated desity kept going up, this kind of negative effect disappeared and it changed into positive effect. When the density attained 15 seedlings/pot, the growth was better than that of control with the concentration of 20μg·mL-1,2μg·mL-1. The result indicated that Baicalensis seedling could have better growth under this condition.
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