Multifunctional bracts enhance plant fitness during flowering and seed development in Rheum nobile (Polygonaceae), a giant herb endemic to the high Himalayas
Multifunctional bracts enhance plant fitness during flowering and seed development in Rheum nobile (Polygonaceae), a giant herb endemic to the high Himalayas
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多功能苞片可增强喜马拉雅山高地特有的巨型草本植物大黄（蓼科）开花和种子发育过程中的植物适应性
DOI：
10.1007/s00442-012-2518-2
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发表时间：
2013-06-01
期刊：
影响因子：
2.7
通讯作者：
Sun, Hang
中科院分区：
文献类型：
--
作者：
Song, Bo;Zhang, Zhi-Qiang;Sun, Hang
特殊化的苞片被认为对某些植物的成功繁殖很重要，并被认为是对不同驱动力的适应。然而，很少有实证研究量化的成本效益框架内的苞片的适应意义。我们探讨了大而艳丽的苞片的繁殖在大黄，一个巨大的草本植物特有的高喜马拉雅山的适应意义。我们研究了苞片是否在开花和种子发育过程中提高生殖成功率。苞片在晴天提高了花和果实的温度，大大降低了到达花和果实的紫外线B（UV-B）辐射强度，并防止花粉粒被雨水冲走。实验结果表明，高温能促进花粉萌发，而雨水和环境水平的UV-B辐射则对花粉造成严重伤害。此外，苞片的去除减少了访花传粉者的数量。开花前或开花后摘除苞片，对种子的繁殖力和后代质量都有不利影响，但传粉昆虫幼虫对种子的捕食作用降低。成本效益分析表明，苞片的成本，即，增加种子捕食，是适度的。结果表明，R. nobile促进花粉萌发，保护花粉粒免受雨水和强烈的UV-B辐射，在开花期间加强传粉者的访问，并在种子发育期间促进受精胚珠的发育。我们认为，多功能苞片的R。nobile是一种有效的适应策略，在高山环境中，可能已经选择，因为非生物环境条件，以及提高授粉成功。
Specialized bracts are thought to be important for the successful reproduction of some plants and are regarded as adaptations to diverse driving forces. However, few empirical studies have quantified the adaptive significance of bracts within a cost-benefit framework. We explored the adaptive significance of large and showy bracts for reproduction in Rheum nobile, a giant herb endemic to the high Himalayas. We examined whether the bracts enhance reproductive success during flowering and seed development. Bracts increased flower and fruit temperature on sunny days, greatly decreased the intensity of ultraviolet-B (UV-B) radiation reaching flowers and fruits, and prevented pollen grains being washed away by rain. Experiments indicated that high temperature could promote pollen germination, while pollen grains exposed to rain and UV-B radiation at ambient levels were seriously damaged. Furthermore, bract removal decreased the number of pollinators visiting flowers. When bracts were removed before or after flowering, fecundity and progeny quality were adversely affected, but seed predation by larvae of pollinators decreased. A cost-benefit analysis demonstrated that the cost of bracts, i.e., increased seed predation, is modest. Our results suggest that the bracts of R. nobile promote pollen germination, protect pollen grains from rain and intense UV-B radiation, enhance pollinator visitation during flowering, and facilitate the development of fertilized ovules during seed development. We conclude that multifunctional bracts of R. nobile are an effective adaptive strategy in alpine environments and might have been selected for because of abiotic environmental conditions as well as for enhancing pollination success.