作 者 ：HUANG Shuang-Quan,GUO You-Hao, PAN Ming-Qing and CHEN Jia-Kuan
Keywords:Liriodendron chinense, Floral syndrome, Visitors, Visiting frequency, Pollination strategy,
Abstract:In studying the relationship between floral syndrome and pollen transfer in an endangered plant Liriodendron chinense (Hemsl.) Sarg., three natural populations in Guizhou, Hunan and Zhejiang Provinces of China were respectively chosen for the field work throughout the florescence. The role of wind-pollination in this species could be ignored as the pollen quantity decreased rapidly with the increasing distance. In spite of morphological protogyny, pollen viability and the life-span of receptive stigmas overlaped more than 24 h. Anatomically, anther sac has four locules with unequally thickened endothecium which may affect anther to dehisce. There were many secretory cells (and groups of fluorescent cells) at the base of petals and styles, but PAS reaction indicated that polyhexose was mostly concentrated in the cells around the vascular bundle of petals. Fluorescent cells and flower fragrance were regarded as attractants, nectar and pollen as rewards to visitors. The floral syndrome seems to be adaptive to insect pollination. During 1994 to 1996, a total number of thirty-nine species of insects including bees, flies and beetles were recognized as the flower visitors. Among which only four were present in all the three populations. The visiting frequency varied distinctly from species to species and among populations. While bees were observed as the most frequent visitors in the population in Guizhou Province, they were substituted by flies in the other two populations in Hunan and Zhejiang Province, and became occasional visitors themselves. The beetles, despite of their frequent activity in flowers, played a much less important role in cross-pollination. Comparing the mean pollen numbers deposited on stigmas pervisit, it was found that bees were much more effective than flies in pollination. SEM examination of insect body also supported this point. Moreover, the visiting frequency was also observed to be closely associated with the characters of flower blossom. Visitors preferred to visit those flowers in early anthesis. Treatments of emasculation and perianth removal showed that the rewards of nectar was more attractive than pollen to pollinators. This species is tend to be cross-pollinated by insects but without its faithful pollinators.
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