| It was hypothesized that allelopathy played an important role in biological invasion. It is well known that Eupatorium adenophorum Sprengel has allelochemicals. However, the relationship between invasiveness and allelopathy is still unknown in E. adenophorum. To understand the relationship, the following three experiments were carried out in this study. (1)To determine the effects of developmental stages on allelopathy in E. adenophorum , mature leaves were collected from E. adenophorum at six growth and developmental stages (from 60 d to 925 d old plants), and their allelopathic effects on seed germination and seedling growth were compared in four native species, Sida szechuensis Mast., Dipliptera roxburghiana Nees, Isodon ternuifolia (D. Don) Kudo and Mariscus cyperinus Vahl. (2) To detect the allelopathic effects of root exudates from E. adenophorum, the invader was mixed in nutrient solution with three native species of Artemisia annual, S. szechuensis and Digitaria sanguinalis, respectively. Macroporous resin was added to nutrient solution to absorb allelochemicals in half of each species combination. Seedling height, root length, branch (tiller) number, total leaf number and mass of root, stem and leaves were measured after three month treatment. (3) To explore the allelopathic effects of E. adenophorum in more nature conditions and to evaluate the relationship between allelopathy and invasiveness of E. adenophorum more comprehensively, the invader was mixed with A. annual, S. szechuensis, Themeda yunnanensis and D. sanguinalis respectively to set up man-made communities. Plant height, basal diameter, branch (tiller) number, crown area and the numbers of new leaves, shed leaves and total existing leaves were measured periodically for seven months. The main results were as follows:1.At high concentrations, the aqueous leaf extracts of E. adenophorum could significantly inhibit seed germination rate and speed, radicle and hypocotyl growth in the four studied...
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