| Stellera chamaejasme, a harmful and poisonous plant, spreads widely on the degraded grasslands in the North China. In this thesis, the allelopathy of S. chamaejasm on its two neighboring plants (Arthraxon hispidus, Galium verum) and soil were carried out. Substances in S. chamaejasme root were extracted by water and ethanol separately, and the influence of the two extraction liquids of different concentrations on seed germination, seedling growth and physiological indexes of the two plants, and changes of soil nutrients and soil microbiological activities between rhizosphere and non-rhizosphere soils of S. chamaejasme were studied. The results showed that the seed germination percentage and germinating process were both inhibited significantly by the original extractions. The inhibition functions of ethanol-extracted liquid were higher than those of water-extracted liquid, and decreased with the concentration. Physiological responses of the plants were induced under extraction liquid treatments. The soluble sugar and protein contents in seeds decreased, while proline content in seeds and malondialdehyde (MDA) content in seedlings increased with weakened superoxide dismutase (SOD) activity. The allelopathy of S. chamaejasm on its neibouring plants is one of the reasons of the vegetation degradation of the grassland. The contents of soil N, P, K, organic matter, microbial biomass C, N, P and the activities of soil enzymes (urease, phosphomonoesterase, protease, saccharase, dehydrogenase, polyphenol oxidase, nitrate reductase) decreased in 0-30 cm layer of the rhizosphere soil compared to those of non-rhizosphere soil. And the changes in 5-30 cm layer were much greater than in 0-5 cm layer. This suggests that the growth of S. chamaejasme can slow down the speed of soil nutrient circulation, decrease the amount of soil microbe, and reduce the soil fertility in the rhizosphere soils. These effects were the main reason of soil degradation in S. chamaejasme grassland.
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