金沙江干热河谷滇榄仁开花物候与繁育系统

通过野外定点观测,并利用套袋实验、解剖实验以及花粉形态特征观察与活力检测、柱头可受性检测、花粉/胚珠比以及异交指数等,研究了金沙江干热河谷滇榄仁自然群体花部形态特征与开花进程、繁育系统特征以及传粉媒介与环境的适应性等内容。结果表明,滇榄仁始花期在每年4月上旬,群体花期持续时间为30d左右,开花同步性高,呈典型的"集中开花模式"。单花开放时,柱头先伸长和膨大,约4d后雄蕊伸出,具有雌雄异熟的特征,一定程度上避免了自交的发生。单花开放进程可划分为花蕾期、柱头伸长期、雄蕊始露期、盛开期、盛开后期、花谢期等6个时期。除了花蕾期外,整个开花期的花粉均具有活力。花粉活力与柱头可受性之间避开了最适授粉期,但也有部分重叠。滇榄仁可能同时具有风媒和虫媒传粉。繁育系统以异交为主,部分自交亲和,需要传粉者。滇榄仁花部特征、开花物候和繁育系统为其适应干热河谷恶劣气候环境提供了一定的生殖保障和进化潜力。良好的群落环境有助于促进滇榄仁异花传粉,产生更多有效的种子,从而促进林下自然更新。

Flowering phenology and breeding system of Terminalia franchetii (Combretaceae) in the dry-hot valley of the Jinsha River, China

Flowering phenology and breeding system characteristics are the most important fitness factors of plants, and have an important influence on plant reproductive success. For example, plants that blossom too early or too late are unable to fruit effectively because of changes to environmental factors or due to the absence of effective pollinators. Terminalia franchetii is a characteristic plant in the dry-hot valley of the Jinsha River, southwest China. The community formed by T. franchetii represents a limited and important type of natural vegetation that grows in this region. However, today, habitat destruction and human disturbance factors are having adverse effects on T. franchetii. Although the plant produces large amounts of fruit, the seed abortion rate is extremely high, resulting in few seedlings and saplings being produced, and, consequently, poor forest regeneration. A number of studies have been conducted on the population diversity of this species, along with studies on the regeneration characteristic of seedlings, seed dispersal and seed bank characteristics, phylogeography, species differentiation, and other aspects. However, studies on the reproductive biology of this plant have not been reported. We conducted a fixed-point field investigation of the floral syndrome, flowering process, breeding system, and adaptability of pollinators to the environment of a natural population of T. franchetii in the dry-hot valley of the Jinsha River, China. The results showed that, each year, T.franchetii begins to bloom in early April, and that the flowering duration of the population is approximately 30 days. The plant has the characteristics of high flowering synchrony, and is a typical "mass flowering" species. When single flowers bloom, the stigma initially elongates and expands. Then, approximately 4 days later, the stamens protrude. Because of this dichogamy, the plant, to a certain extent, avoids self-pollination. Flowering is divided into 6 stages; namely, the bud stage, stigma elongation stage, early stamen showing stage, blooming stage, late blooming stage, and flower withering stage. In addition to the bud stage, the pollen is viable throughout the entire flowering period; although, the strongest vitality of the pollen occurs during the early stamen showing and blooming stages. Optimum pollination is avoided due to the asynchrony between pollen vitality and stigma receptivity; however, there is a certain degree of overlap between the two stages. T. franchetii might be adapted to both wind and insect pollination. In the breeding system of this species, out-crossing is predominant and, although partially self-compatible, it requires pollinators. The main pollinators are flies, such as Episyrphus sp., Chrysomyia megacephaia, Apis cerana, Sycanus croceus, and Delta conoideum. The floral characteristics, flowering phenology, and breeding system of T. franchetii provide some reproductive assurance and evolutionary potential for its ability to adapt to the complex and extremely harsh environment of dry-hot valleys; however, a favorable community environment contributes to the promotion of cross pollination of T. franchetii and more effective seed production; thus, promoting natural forest regeneration.