荒漠孑遗植物裸果木的花部特征及繁育系统

Floral syndrome and breeding system of Gymnocarpos przewalskii Maxim

裸果木是亚洲中部荒漠区少有的第三纪孑遗物种,也是构成石质荒漠植被群落的重要建群种之一,由于人为干扰,其自然种群处于不断衰退中。本文通过野外观察和人工授粉实验等方法,对裸果木的花部特征及繁育系统进行研究,对于揭示该物种生活史特征并探讨影响其生殖成功的因素及制定相应的保护和管理策略具有重要意义。结果表明:裸果木为两性花,花小,无花瓣,雄蕊10枚,外轮5枚雄蕊败育,胚珠1枚,开花盛期有少量花蜜并散发浓烈难闻气味,花粉活力和柱头可授性之间存在46 h的重叠期,且不完全雌性先熟,柱头和花药在多数花的单花花期结束时并未接触,因此,裸果木花主要表现为适应异花传粉的雌雄异位特征;花粉/胚珠比(P/O)为1371.67±236.21,异交系数(OCI)为3;不同花粉来源(自然授粉、自花授粉、同株异花和异株异花授粉)的花粉在柱头上均能萌发,但花粉管生长速度存在差异,同株异花授粉和异株异花授粉的花粉管生长速度较快,自花授粉的花粉管生长速度最慢且部分花粉管(43%)在到达子房时停止生长,并未到达胚珠;人工套袋实验的结果表明,裸果木不存在无融合生殖,自然结种子数低,自然授粉花的种子数远远低于人工异株异花授粉花,说明存在由于异花传粉者不足造成的传粉限制。裸果木部分雌性先熟和雌雄异位是两性花为避免雌雄功能重叠,促进异交而采取的一种花部机制,其繁育系统为兼性异交类型且需要传粉者,部分自交不亲和和传粉限制是影响该物种有性生殖成功的主要因素。

GTmnocarpus przewalskii, a raze Tertiary relict species in the desert region of Central Asia, is a vital constructive species that constitutes the stony desert vegetation community, and its natural population is declining due to human interference. In the present study, based on field observations and artificial pollination experiments, we investigated the floral characteristics and breeding system of G. przewalskii, which are highly important for revealing its life history characteristics, discussing factors that affect the success of its reproduction, and developing conservation and management strategies. G. przewalskii is a plant with bisexual flowers that are small and apetalous. Each flower has 1 ovule and 10 stamens, with the 5 outer-whorl stamens being abor- tive. During anthesis, the flower has a small amount of nectar with strong unpleasant odor. During this period, there is a 46-hour overlap between pollen viability and stigma receptivity and the in- complete female becomes mature first; in addition, the stigma does not come in contact with the anthers when the uniflorous florescence of most flowers ends. Thus, G. przewalskii flowers mainly exhibit herkogamy and adapt to cross-pollination with a pollen/ovule （P/O） ratio of 1371.67 ± 236.21 and outcrossing coefficient of 3. Pollen from different sources （natural pollination, selfpollination, geitonogamy, and xenogamy） can all germinate on the stizma, but the erowth rntes of the pollen tubes vary. In geitonogamy and xenogamy, the pollen tubes grow faster, while in self-pollination, the growth is slowest, with growth ceasing in part of the pollen tube （43%） as it approaches the ovary, thereby it is not able to reach the ovule. The experimental results of artificial bagging show that G. przewalskii is apogamous and has few naturally born seeds, and the number of the seeds of naturally pollinated flowers is much lower than that of artificial xenogamous flowers, indicating the existence of pollination restriction caused by the insufficiency of cross-pollinators. Partial protogyny and herkogamy in G. przewalskii are a floral mechanism adopted by the bisexual flowers to avoid the functional overlap of males and females and to promote outcrossing. The breeding system of G. przewalskii is facultatively xenogamous and it requires pollinators. The success of its sexual reproduction is mainly affected by two factors, partial selfincompatibility and pollination restriction.