Abstract: The Ward’s minimum variance method was used to classify plant community types through plot survey in the fluctuation area of Chongqing section of Yangtze River. We analyzed plant species diversity in the communities and the effects of nine environmental factors on community distribution patterns using Canonical Correspondence Analysis (CCA). The survey recorded a total of 419 vascular plant species from 286 genera and 103 families. Compositae and Gramineae were dominant families. The fluctuation area was divided into 18 community types, including two shrub communities and 16 grass communities. The occurrence frequency of Form. Cynodon dactylon+Paspalum thunbergii+Eclipta prostrata was the highest. Altitude was significantly negatively correlated with soil water content, soil organic matter content, available phosphorus content and substrate type, and positively correlated with diversity index. The interpretation of the spatial distribution of plant communities by the first axis of CCA was 8.91%, accounting for 41.21% of total interpretation, which better explained the relationship between community and habitat. The distribution of plant communities was affected by the combination of various environmental factors. Among all the environmental factors, altitude and soil water content played a leading role. Shannon diversity index, Pielou evenness and Gleason species richness in the falling zone increased with elevation, while Simpson dominance showed opposite trend. The dissimilarity index and Cody index increased with elevation. Those results suggested that plant community of the fluctuation area was at the primary stage of succession, and that the ecosystem was unstable. The distribution and diversity of plant communities in different elevations were different. Flooding was the main factor accounting for such difference. Our results can lay a theoretical foundation and practical basis for the monitoring, protection and ecological restoration of the fluctuation area of Chongqing section of Yangtze River.

Key words: seedling accumulation, stable nitrogen isotope, ^15N labeling method, seed dispersal.