[Analysis of reproductive ecological factors of endangered Rhodiola gannanica.]

To find effective ways for protecting and recovering an endangered species Rhodiola gannanica in Gannan, an important distribution region of this species in the eastern Tibetan Plateau of China, the breeding system, reproductive process, flowering phenological characteristics and other reproductive controlling factors were investigated. The results showed that there was a unique breeding system in R. gannanica, which was dioecious, and male flowers were also bisexual plants in the early stage of flower bud differentiation. While the sac of pistil was aborted in a certain stage with the development of flowers, the bisexual plants only played the role of males' functions. The outcrossing reproduction was observed, the pollination mode was mainly by wind, and the population flowering occurred in the season with abundant precipitation and high temperature. The bud satge appeared in early June, the florescence was in mid-June, and the flourishing florescence was in early July. The flo-wering duration of R. fastigiata was about 36 d, and the fruit ripening began in late August. The flo-wering time and the flowering duration of the bisexual plants were earlier than female plants. Due to the low pollination rate of the female plants, the buds and ovules were damaged and the 1-3 years young plants barely got flowering and fruiting, the rate of flowering and fruiting of the community only reached 11.0% and the rate of seed natural propagation was low (about 2.0%). 20.0%-25.1% buds of female plants were damaged from bud to flowering stages. 51.1%-65.0% flowers were aborted from flowering to fruiting stages. Only 10.1%-21.0% of ovules developed into seeds. The seed production of per female plant was 158.1, seed germination rate was 81.5% under artificial conditions, and seedling survival rate reached 36.0% in the first year. Our results revealed that seed quality was not the key ecological factor, while it was the pollen limitation, low seed production and the survival rate of seedling that resulted in the reproductive success and species endangered situation.