Permalink : http://hdl.handle.net/2115/38222

KEYWORDS : Populus euphratica;risk-sharing;seed rain;sexual reproduction;temporal heterogeneity

The seed rain of Populus euphratica in Ejina Oasis was continuously studied in the years of 2004, 2006, 2007, and 2008. The duration of P. euphratica seed rain in a community was usually 2 to 3 weeks, with a peak period of 7 to 14 days. Approximately 90% of the total number of seeds were dispersed in the peak period, and for a single day most seeds fell between the hours of 10:00 to 16:00. It was found that the seed rain of P. euphratica was determined by a combination of biological rhythms and weather conditions. Wind speed and atmospheric humidity were the two main meteorological factors influencing seed dispersal. More seeds fell when there was higher wind speed and lower RH. After we completed our comprehensive study of the P. euphratica seed rain, temporal heterogeneity was found not only in different populations but also in different individuals, and not only in different phases of the seed rain but also in different times of the day. P. euphratica extends its seed rain season by these different kinds of temporal heterogeneity to ensure some propagules survive and germinate when floods occur. Furthermore, marked inter-annual fluctuation in the seed rain exists in P. euphratica in the study area. Finally, in relation to the water supply for P. euphratica in Ejina in recent years, we concluded that there is no dislocation in time of water supply and the seed rain of P. euphratica in Ejina Oasis, and the reason for the failure of sexual reproduction of P. euphratica may lie in the human disturbances of channeling and the cement lining of the channels.