青藏高原特有植物祁连獐牙菜(龙胆科)的花综合征与虫媒传粉

Floral syndrome and insect pollination of the Qinghai-Tibet Plateau endemic Swertia przewalskii (Gentianaceae)

雌雄异熟和异型花在一些被子植物中的共同存在被认为是一种有效避免两性花植物自交并促进异交的机制。本文报道青藏高原特有植物祁连獐牙菜SwertiaprzewalskiiPissjauk .的花同时具有雌雄异熟和异型花这两种特征。在此基础上 ,我们详细观察了该植物访花昆虫的访花行为 ,主要探讨这种促进异花传粉的机制是否能完全避免株内异花传粉的自交。繁育系统试验证明祁连獐牙菜单花套袋不结实 ,说明雌雄异熟和异型花的花特征完全避免了单花的自花传粉 ,自然结实必须依赖昆虫传粉才能完成。然而 ,该植物却是高度自交亲和的 ,因为人工株内异花自交具有较高的种子结实率。每个植株在盛花期开放 1 - 6朵 ,平均具有 3朵开放的雄性期或者雌性期的花 ,二者的比例为 2∶1 ,在植株上的分布没有规律。我们观察到多种昆虫访问该植物的花 ,其中 ,克什米尔熊蜂BumbuskeshimirensisFriese和蜜蜂ApismelliferaL .是该植物最常见与最有效的传粉者。进一步的观察发现 ,这两类传粉昆虫对雌性阶段和雄性阶段的花的访问没有选择 ,但在一个植株上访花顺序的总体趋势是由下向上的。它们在同一植株上访花数超过 1朵的访问比例约占 37.1 %。因此可以初步推断 。

A combination of dichogamy and herkogamy in hermaphroditic plants is an effective mechanism to encourage outerossing and avoid selfing. In this paper, we studied whether such a mechanism completely avoids geitonogamous selfing in Swertia przewalskii Pissjauk., a perennial endemic to the Qinghai-Tibet Plateau. We studied the floral syndrome of this species and found that its flowers are characteristic of dichogamy and herkogamy. Each individual plant of this species has an average of three flowers ranging from one to six, at both staminate and pistillate stages with a ratio of 2: 1 in full anthesis. No autonomous selfing was found in the breeding experiments, indicating that this species is pollinator-dependent for seed. But artificial selfing production for geitonogamy produced high seed set, which implies that selfing can not be completely avoided if effective pollinators move continuously between flowers within an individual plant. A variety of insects were observed to visit S. przewalskii, but the most effective and common pollinators were Bumbus keshimirensis Friese (Bumbidae) and Apis mellifera L. (Apidae). A further statistic observation of these two effective pollinators indicated that they showed no preference to either staminate or pistillate flowers but always visited them from the lower flowers to upper ones within individuals. We further calculated the frequency of their visits between and within individual plants. Among the pollinators' bouts, the proportion of geitonogamous visits within an individual plant occupied about 37%. Such a case implied that geitonogamous selfing was not avoided in S. przewalskii in spite of floral dichogamy and herkogamy, suggesting that dichogamy and herkogamy in hermaphroditic plants play a more important role in reducing interference between male and female function than in encouraging outerossing.