Abstract: Competitions between plants run through plants whole life history, bringing important effects on  plant growth and propagation. Based on the plant survey in the water-level fluctuation zone of Three Gorges Reservoir, this paper analyzed the intra- and inter-specific competitions in dominant species Xanthium sibirium community in the zone. The average height of the community was 1.4 m, the coverage was 90%, and the abundance was 40. The highest height of the individuals was 2.6 m, and the maximum biomass was 1622.3 g. The competition intensity between the plants decreased with distance (P<0.01). When the distance between plants was 0-10 cm, the competition was the strongest; when the distance was 0-30 cm, the competition was strong, and inter-specific competition was stronger than intra-specific competition. With the increasing distance between plants, the individual number and plant height of dominant species increased, and the biomass, seed yield, and branch number increased after an initial decrease. The plant species with high propagation capability and growth rate had the advantage in competition, which ensured their survival in the water-level fluctuation zone.

Key words: Housefly larvae, Panaeus chinensis, Baculovirus, Prophenoloxidase, Population infection model