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Ageratina adenophora (Spremgel) R. King and Robinson (Synonym:Eupatorium adenophorum), originally found in Mexico and Costarica, is a notorious invasive weed worldwidely and one of the most serious invasive species in China, and it has caused great economic loss and threatened native biodiversity. This research isolatated and identified the allelochemicals from root exudate of A. adenophora, and examined the allelopathic of the main components, then studied the impacts of the main allelochemical on organic phosphate bacteria. The main results were showed as follow:1. Examined the allelopathy of the leachate from the water raising A. adenophora and the root exudate of A. adenophora on the growth of alfalfa (Medicago sativa L.), which is a common pasture grass in southwest China. The results showed that the two could significantly inhibite the growth of alfalfa. The inhibitive effect on growth of alfalfa increased with the increase of the leachate’s concentration,10%>5%>3%>1%>CK. Comparied with the control, the allelopathic effect indexes of leachate from the root of A. adenophora to the root length of alfalfa were:-0.12,-0.32,-0.79,-0.88(from 10% to 1%), to the shoot length were:-0.12,-0.32,-0.79,-0.88;-0.08,-0.15,0.54,0.63. And the allelopathic impacts of root exudate on alfalfa’s root length, shoot length and fresh weight reached 51%,79%, and 69% respectively.2. Isolated the allelochemicals from root exudation of A. adenophora cultivated in water by High Performance Liquid Chromatography (HPLC) and chromatography then elucidated the structure of them by Nuclear Magnetic Resonance (NMR) and Electrospray Ionization/Mass Spectrometry (ESI-MS). The result showed that 7 chemicals were isolated from the root exudates, including ageraphor-dione,9-oxo-ageraphorone, eupatorenone,9-hydroxy-ageraphor-one, encecalin, dibutyl phthalate and bis (2-ethylhexyl) phthalate, among which encecalin, dibutyl phthalate and bis (2-ethylhexyl) phthalate were found in A. adenophora for the first time.3. Afterward alfalfa was used to examine the allelopathic activity of ageraphor-dione, eupatorenone,9-oxo-ageraphorone, dibutyl phthalate and bis (2-ethylhexyl) phthalate. And dibutyl phthalate was found to have the strongest allelopathic inhibition to the growth of alfalfa, the allelopathic effect indexes to the root and the shoot were-0.19 and-0.48 respectively, at the concentrations of 500mg/L. Followed by ageraphor-dione. the allelopathic effect indexes were-0.15 and-0.42. On the other side, at the low concentration of 50mg/L 9-oxo-ageraphorone can promote the growth of alfalfa root length and its allelopathic index was+0.14, for moderate concentration of 100mg/L it reached+0.24.4. By measuring the growth curve the impact of dibutyl phthalate on soil organic phosphorus bacteria was determined. The results showed that at the low concentration (50mg/L, 100mg/L. 200mg/L), dibutyl phthalate can promoted the growth of organic phosphate bacterium, but at higher concentration (500mg/L and 1000mg/L), dibutyl phthalate can inhibited the growth of the bacterium. In addtion dibutyl phthalate can advance the logarithmic phase of organic phosphorus bacterium, thus promoting the proliferation of it. This suggested that dibutyl phthalate, one main allelochemical of the root exudate from A. adenophora, played an important role in the process of the conversion of the nutrition to be easily accessed by soil microbiology.
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