Abstract: In order to reveal the adaptability of dominant plants to the environment and the interspecies relationship of the dominant plants in the Three Gorges Reservoir's water-level-fluctuating zone, the primary tributary of the middle and upper transition zone of the Three Gorges Reservoir was taken as the research object. Based on the survey of sample plots in the study area, niche width and niche overlap indicators were used to analyze and discuss the niche characteristics of dominant plants. The results showed that the dominant species, Cynodon dactylon,Bidens pilosa,Xanthium sibiricum,Echinochloa crusgalli,Alternanthera philoxeroides, and Digitaria sanguinalisas generalized species accounted for 37.50% of the total number of species, which had the characteristics of wide distribution and strong adaptability. It can be used as a pioneer species for vegetation restoration in the hydro-fluctuating zone of the Three Gorges Reservoir. The number of species pairs of dominant plants in the dry and tributary water-level fluctuating zones with a niche overlap value> 0.5 was 40 and 50, respectively, and the number of species pairs with a niche overlap value of 0 was 27 and 13, respectively. The competitiveness between them was relatively weaker than that of the tributaries. The dominant plants in the dry and tributary water-level fluctuating zones near the estuary of the Quxi River mostly overlap in unequal-width niches, achieving niche sharing to a certain extent; a few plants had overlapping niches and do not participate in competition. The niche overlap of dominant plants had differences in trunk and tributaries and differences in elevation. The differentiation and identification of generalized species and specialized species of dominant plants play a vital role in enriching regional species composition and ecological restoration.

Key words: Three Gorges Reservoir, water-level-fluctuating zone, dominant plants, niche width, niche overlap