开花时间与伴生种对鹤首马先蒿传粉和生殖成功的影响

Effects of flowering date and co-flowering species on pollination and reproduction in Pedicularis gruina

开花物候是物种间相互作用的重要生活史特征和适合度因子,在全球气候变化的背景下而备受关注。为探讨开花时间如何在种内和种间水平上影响植物的传粉和生殖成功,我们连续3年(2003-2005)对不同花期和伴生种存在情况下的鹤首马先蒿(Pedicularisgruina)的传粉者访花忠实度、受粉率、坐果率、单果种子产量和果实被啃食频率进行了比较研究。结果表明鹤首马先蒿的坐果率主要受其传粉环境的影响:在没有伴生种时,不同时期鹤首马先蒿的坐果率没有显著差异,34-38%的花可以坐果;在有伴生种存在时既可以显著提高其坐果率,也可显著降低其坐果率,这取决于传粉者类型以及伴生种密穗马先蒿(P.densispica)花期的差异。密穗马先蒿具有花蜜和花粉双重报酬,在群落中可以作为主体物种吸引传粉者并间接促进与其伴生的鹤首马先蒿的传粉和生殖成功。同样无蜜的管花马先蒿(P.siphonantha)和鹤首马先蒿伴生,则是通过提高群落水平对传粉者的吸引力进而直接促进鹤首马先蒿的传粉和生殖成功。此外,研究结果也表明开花时间对坐果率没有显著影响,但是显著影响单果种子产量和果实被啃食的频率。在相同的传粉条件下早花期植株单果种子产量显著高于晚花期的种子产量,同时早花期的果实被啃食的频率显著增加。

Flowering date along with interactions of other co-flowering species may be factors that determine pollination and reproductive success of a focal plant species. We investigated an alpine bumblebee-pollinated herb Pedicularis gruina to assess the effects of flowering date and co-flowering species on pollination, reproduction, and predation over a three year period （2003-2005）. We analyzed pollen load of bumblebees to determine floral constancy, and calculated pollination rates of flowers, fruit set, seed production per capsule and the percentage of seed predation. We found that fruit sets did not differ significantly among years and between different flowering dates when there were no co-flowering species, with 34-38% of flowers pro- ducing fruits. However, the presence of co-flowering species could either increase or decrease the pollination and reproduction in P. gruina, which depends on pollinator type and flowering date of the co-flowering species P. densispica. Pedicularis densispica enhanced pollination and reproduction through increased floral resource diversity, whearas P. siphonantha enhanced pollination and reproduction through increased attractiveness with larger displays. Flowering date did not affect fruit set, but significantly affected seed production and seed predation. Seed production decreased significantly at later flowering dates given the same pollination condition（i.e., no co-flowering species, pollinator competition, or facilitative pollination）. However, fruits produced in early flowering periods suffered more severe seed predation compared to those in later flowering periods.