云南草寇花序内不同部位的性分配

Variation in floral sex allocation within inflorescences of Alpinia blepharocalyx

关键词:  云南草寇, 部位, 性分配, 花粉数, 胚珠数, 异型异熟

Key words:  Alpinia blepharocalyx, positions, sex allocation, pollen number, ovule number, heterodichogamous

摘要:

两性花植物花序内的性分配常存在差异,资源竞争、结构效应、交配环境(雌雄异熟、传粉者定向访花行为等)或授粉不均匀等几种假说可以解释这种现象。为验证上述假说,该研究以云南草寇两种表型(雄先熟型和雌先熟型)为材料,分析了其花序内不同部位(基部、中部和顶部)的每花花粉数、胚珠数、花粉/胚珠比、结实率和结籽率,花序内传粉者的定向访花行为,以及人工辅助授粉和去花处理对结实率和结籽率的影响。结果表明:两种表型花序内每花花粉数不随部位而变化,每花胚珠数、结实率和结籽率由基部到顶部依次降低,每花花粉/胚珠比由基部到顶部依次增加,表明顶部花存在偏雄的性分配。人工辅助授粉后,结实率、结籽率仍由基部到顶部依次降低,表明授粉不均匀假说不能解释云南草寇花序内不同部位结实率、结籽率的差异。去除基部和中部花后,顶部花人工辅助授粉条件下的结实率、结籽率与基部花人工辅助授粉条件下的结实率、结籽率无差异,表明云南草寇花序内不同部位结实率、结籽率的差异主要由资源竞争引起。雌先熟表型每花花粉数、花粉/胚珠比高于雄先熟表型,表明两种表型存在性分配差异。传粉者主要先访问云南草寇基部的花,然后向顶部移动。云南草寇花序内顶部偏雄的性分配可能是由资源竞争和传粉者定向访花造成的。

Abstract:

Intra-inflorescence variation in floral sex allocation is commom in hermaphroditic plants, and several non-exclusive hypotheses, including resource competition, architectural effect, the mating environment or non-uniform pollination, have been formulated to explain this phenomenon. To test the above hypotheses, we investigated floral sex allocation within racemes of two morphs in heterodichogamous Alpinia blepharocalyx. Flowers on each raceme were sampled and assigned to one of three relative positions: basal, middle and distal, variations in pollen number, ovule number, the pollen/ovule(P/O)ratio, and fruit and seed production among positions within racemes were quantified. Ecological causes for fruit and seed production were evaluated by flower removal and supplemental pollination, directional movements of pollinators within racemes were also observed. Pollen number per flower did not change with relative positions, ovule number per flower declined from basal to distal postions, and the P/O ratio per flower increased from basal to distal positions in both morphs, thus distal flowers performed male-biased function. Under natural pollination condition, fruit and seed set declined distally in both morphs, therefore, female reproductive success at the relative postions showed the same pattern as that of sex allocation at flowering stage. After hand-supplemental pollination, both fruit and seed set decreased from basal to distal positions in each morph, thus, lower female reproductive success at distal postions could not be attributed to pollen limitation. After the removal of basal and middle flowers, the fruit and seed set of distal flowers did not differ from those of basal flowers when extra pollen was added, indicating that the low fruit and seed set of distal flowers was simply attributed to resource competition rather than architectural effect. Pollen number and the P/O ratio was hi-gher for protogynous than protandrous morph, but fruit and seed set did not differ between morphs, indicating that sexual specialization occurred at flowering stage. Pollinators tended to visit basal flowers first and then moved upwards within an inflorescence, which would result in directional pollen flow from basal to distal flowers. Both inter-flower resource competition and directional pollinator movement may be responsible for intra-inflorescence variation in floral sex allocation of A. blepharocalyx.