Abstract: Studies on the allelopathy of Ageratum conyzoides aqueous extract showed that the aqueous extract significantly inhibited seed germination and seedling growth of all tested plants at 0.25 g FW·ml^-1 ,but the inhibition disappeared at 0.10 g FW·ml^-1 . The allelopathic potential of aqueous extract from different organs of A.conyzoides and from its different development stages, especially from different habitats, was different. Ageratum conyzoides growing in adverse habitat showed a stronger allelopathic potential.Three allelochemicals from aqueous extract,e.g. precocene Ⅰ,precocene Ⅱ and stigmast 5,22-diene-3βol,were isolated and identified.

Key words: Ageratum conyzoides, Allelopathy, Allelochemical, Isolation and identification, Habitat, soil respiration, carbon flux estimation, sampling strategy, region division