Abstract: Abstract:【Objective】 The experiment was conducted to investigate the intra- and inter-specific competition interaction between Ageratina adenophora (Sprengel) R. King & H. Robinson and Setaria sphacelata (Schum) Stapf ex Massesy cv. Narok at different densities and its succession in the field, and to further explore the methods of controlling the invasive weed A. adenophora displaced by S. sphacelata.【Method】 We grew two perennial grasses species (A. adenophora and S. sphacelata) for 2 yr in monoculture and in mixture on an experimental densities gradient. The above- and blow-ground biomass of two species were measured and the growth response and relative competitive ability were discussed.【Result】 The biomass total and relative yield (RY) and competitive balance index (CB) of S. sphacelata were significant higher than those of A. adenophora, the relative yield total (RYT) was significant lower than 1. The relationships mentioned above become more obvious with density decreasing. The total biomass of A. adenophora at the densities of 19, 46 and 174 plants/m2 in mixture decreased by 33.0%、38.5％ or 70.1% compared to those in monoculture, respectively. However, the total biomass of S. sphacelata at the same density between in monoculture and in mixture showed no significant difference. The ratios of root mass: shoot mass of S. sphacelata in mixture were significant lower than those in monoculture. However, the ratios of root mass: shoot mass of A. adenophora in the mixture were significant higher than those in monoculture.【Conclusion】There was significant mutual antagonism between A. adenophora and S. sphacelata. Compared to A. adenophora, the relative competitive ability of S. sphacelata was higher which decreased heavily the growth of A. adenophora mainly by shoot competition. It will be a good strategy for controlling of A. adenophora and restoring its invaded habitats by S. sphacelata in the future.

Key words: Ageratina adenophora, Setaria sphacelata, Plant competition, Ecosystem restoration, Weed control