灌木铁线莲繁育系统特征及其花下垂现象的适应性意义

Breeding System Characters and the Adaptive Significances of Downward Orientation Flowers in Clematis fruticosa Turcz.

该研究对兰州市北山地区自然居群下的灌木铁线莲(Clematis fruticosa Turcz.)的繁育系统特征进行了实验分析,并通过对其花朵进行人工上举处理,研究了花朝向改变(花朵上举)后访花昆虫、花粉数量和质量变化以及结籽率和种子特征的变化,以此反证花朵下垂的适应性意义。结果表明:(1)自然状态下,灌木铁线莲的P/O值为9579.5,属于专性异花授粉;套袋实验结果显示,灌木铁线莲自交亲和,兼具异交和自交的混合交配系统,但不存在无融合生殖现象。(2)灌木铁线莲的主要传粉者为东亚无垫蜂(Amegill aparhypate)和中华蜜蜂(Apis cerana);人工上举处理改变花朝向后,两种传粉昆虫的访花频率和单花停留时间与自然条件下没有发生变化,但因雨水冲刷造成其花粉数量显著下降,且阳光直射使花粉活力显著下降,说明花朝向改变会降低其雄性适合度。(3)花朝向改变后,灌木铁线莲结籽率显著下降,种子宿存花柱长度降低,但并没有影响种子大小和千粒重,说明花朝向改变降低了雌性适合度,并影响到灌木铁线莲种子传播。研究结果证实,灌木铁线莲花期花朵下垂现象对有效传粉昆虫影响不大,但可以显著提高植物雄性适合度和雌性适合度,并作为一种有效的适应策略保障了其繁殖成功。

In this study, we tested the breeding system characters of Clematis fruticosa Turcz., which were selected in the natural population at Lanzhou Beishan. And also, by changing flower direction from facing down to up, we studied the visited insect attracting, pollen quantity and quality changing, seed setting ratio changing, and the seed characters of C. fruticosa. The results showed that：（1） in natural, the P/O of C. fruticosa was 9 579.5, which showed out an obligate cross pollination breeding system; bagging experiment results showed that the C. fruticosa was self compatible, and had a mixed breeding system which combined with selfing and crossing, but no apomixes was tested. （2） The main pollinators of C. fruticosa were Amegill aparhypate and Apis cerana; after flowers artificially erected. The visit frequencies and stay time/visit/flower did not differ significantly with the natural, but the pollen numbers after rainwash decreased significantly, and as well as the pollen vitality after exposed to solar radiation, which indicated that flower direction changing could decrease the male fitness. （3） After the flower direction changed, the seed setting ratio of C. fruticosa decreased greatly, and the persistent styles of the downwards flowers were significantly longer than that of upwards, but the seed sizes and seed weights did not differ significantly, which indicated that the flower direction changing could decrease the female fitness, and also could influence the seed dispersal of C. fruticosa. The results suggested that the flower drooping of C. fruticosa could not influence the effective pollinators, but could significantly increase the male and female fitness, which may act as an effective adaptive strategy for the reproductive success of C. fruticosa.