新疆党参的花部综合征与次级花粉呈现

Floral syndrome and secondary pollen presentation in Codonopsis clem-atidea(Campanulaceae)

次级花粉呈现是植物提高花粉输出和接受的效率与准确性以及促进异交的一种繁殖策略。新疆党参(Codonopsis clematidea)具有典型的次级花粉呈现特性。本文采用野外观测、授粉实验与室内显微观测等方法,对该物种的花部综合征及其次级花粉呈现过程进行了详细观测,并对这些特征的适应意义进行了探讨。结果表明:新疆党参钟状下垂的蓝色花冠及黑黄色蜜腺,不仅避免了雨水冲刷雌雄蕊、稀释花蜜以及风移出花粉等不利影响,还增加了对传粉者的吸引,延长了花粉活力及柱头可授性持续时间。次级花粉呈现属于亚顶端花柱呈现者,呈现机制为沉积机制。该特性限制了单个传粉者带走的花粉量,延长了花粉呈现时间,使更多传粉者参与传粉过程,增加了雄性适合度。其雄性先熟及雌雄蕊空间位置变化,避免了雌雄功能干扰,为传粉者取食花蜜、输出花粉以及柱头接受异源花粉提供了通道和机会。其泛化传粉系统的主要传粉昆虫为林野熊蜂(Bombus silvarum)、草地熊蜂(B.paradoxus)和树长黄胡蜂(Dolichovespula sylvestris),其较长的单花花期(6d左右),昆虫访花高峰期与花粉活力最高时期及柱头最佳授粉期相吻合,以及较大的泌蜜量、较高的花蜜糖浓度和较长的泌蜜时间等特征,可提高传粉者的访花频率,增加成功传粉的机会和传粉效率。在气候多变的天山山区,该物种特殊的花部综合征和次级花粉呈现机制对提高其传粉效率并促进异交繁殖成功具有重要意义。

Secondary pollen presentation has been described as a reproductive strategy that enhances the ef-ficiency and accuracy of pollen exportation and pollen reception,thereby promoting outcrossing.Codonopsis clematidea is characterized by secondary pollen presentation.The objective of this research is to study the floral syndrome and the procedure of secondary pollen presentation of this species,with special reference to the adaptive significance of these features based on the field observations,hand-pollination experiments and indoor microscopic observations.The results showed that the blue campanulate pendulous corolla and black and yellow nectary of C.clematidea not only protect the androecium and gynoecium from rain damage and prevent rain water from diluting the nectar and removal of pollen by wind,but they also attract more pollina-tors and extend the duration of pollen viability and stigma receptivity.The secondary pollen presentation of this species is sub-terminal stylar presenters and belongs to the deposition mechanism.This character limits the amount of pollen removed by the pollinators and prolongs pollen presentation,thus attracting more polli-nators and thereby increasing male fitness.The protandry and the change of the spatial position of male and female organs during the flowering stage of C.clematidea not only avoid interference between male and fe-male functions,but also create a passageway for pollinators to forage for nectar and pollen and for stigmas to receive outcross pollen.Bombus silvarum,B.paradoxus and Dolichovespula sylvestris are the effective pol-linators in the generalist pollination system of this species.Other floral characteristics of this species,such as long flowering duration（approximately 6 d） per flower,overlap of the peak of insects visitation in the male and female phases with the period of highest pollen viability and the optimal stigma receptivity of pollen,lots of nectar that contains a higher sugar concentration and a long period of nectar secretion during the flowering stage,etc,enhance visitation frequencies and the chances of successful pollination.Therefore,these traits help improve pollination efficiency and promote outcrossing.The special floral syndrome and the mechanism of secondary pollen presentation are significant in improving pollination efficiency and promoting the repro-ductive success of Codonopsis clematidea by outcrossing under changeable weather conditions in Tianshan Mountains.