Effects of water level regulation on the seed germination and production of annual plant Xanthium sibiricum in the water-level-fluctuating-zone of Three Gorges Reservoir.

Vegetation effectively slows down the deterioration rate of the ecosystem in the water-level fluctuation zone (WLFZ). In this study, we investigated the impact of impoundment on the germination of seeds from Xanthium sibiricum fruits with various degrees of maturity and produced by X. sibiricum plants growing at different elevations in the WLFZ. Seed production by X. sibiricum under the current water level regulation mode was also investigated. Seeds were collected from seven elevations of the WLFZ of Three Gorges Reservoir (TGR) and exposed at these elevations to submergence. Seed production of the plants germinated from X. sibiricum seeds was observed. The maturity degree of X. sibiricum fruits from different elevations has no influence on the seed production by the plants that are produced from the fruits. Under the present water-level regulation mode, X. sibiricum growing above 155 m are able to generate mature seeds and thus provide seed sources for population maintenance, although the plants growing at an elevation below 165 m failed to produce fruits in 2010 due to unusual flooding. This study is useful for the vegetation recovery and reconstruction in other regions with hydrological characteristics similar to that of the TGR.