濒危植物独花兰的传粉生物学初步观察

独花兰(Changnienia amoena Chien)为我国特有的单种属植物，近年因生境破碎化和过度采挖，其野生资源日渐减少。迄今对独花兰极为有限的研究表明，其结实率很低或根本不结实，其传粉媒介也一直未被发现。2002年3～4月，我们对神农架2个移植居群和5个天然居群进行了传粉生物学的定点观察，发现雌性三条熊蜂(Bombus (Diversobombus)trifasciatus Smith)、仿熊蜂(Bombus (Tricornibombus) imitator Pittion)和蜜蜂均访问独花兰，但只有二条熊蜂身体粘有花粉块，是独花兰的有效传粉者。三条熊蜂的访问频率很低，在113h的观察中只有9次访问，但在一个天然居群(population 3)中曾观察到一天4次的最高访问频率；访问主要在12：00～15：00出现，但在花上停留时间很短，不超过10s。在末被授粉的情况下，独花兰花朵大约3周后自然枯萎，但受粉后3、4d内即出现～系列形态和颜色的变化，包括花梗逐渐伸长，子房在花梗逐渐停止伸长后开始膨大等，表明花梗伸长可作为结实(授粉成功)的指标。人工授粉实验表明，自花、异花受粉后花梗均伸长，而套袋隔离花的则花梗不伸长，说明独花兰是自交亲和的异交种，需要昆虫传粉。根据传粉者的访问频率、居群中果实的分布，尤其是花距内无花蜜等特征，我们认为独花兰是一种欺骗性传粉的兰花。相对于其他欺骗性传粉的兰花，独花兰的自然结实率并不很低(26．98％)，这与居群规模小会提高欺骗性传粉兰花结实率这一观点吻合。花粉块的输出数远高于结实数，这说明独花兰存在一定的花粉浪费。

A Preliminary Study on Pollination Biology of an Endangered Orchid, Changnienia amoena, in Shennongjia

Changnienia amoena Chien is a monotypic species and endemic to China, and was listed onthe Chinese Red Book in 1992. The species was once abundant but has become rare and endangered inrecent years because of the habitat fragmentation and unduly commercial collections. Previous observa-tion showed that this species has very low and even no fruit set, and the pollinators are not observedbefore this report. The present observation was conducted at the Shennongjia, Hubei Province during thespring of 2002. The results showed that Bombus (Diversobombus) trifasciatus Smith? B. imitator Pittionand one species of Apis visited the flowers of the orchid, but only B. trifasciatus could carry pollinaria on itsbody and was the legitimate pollinators of C. amoena. During 113 h of observation, only nine visitationswere recorded. The bumblebees mainly appeared during 12:00-15:00 during the day. Bumblebees stayed ina flower only a few seconds and never more than ten seconds. The flowers would persist in fresh for aboutthree weeks when they were not pollinated, but 3 or 4 d after pollinated, the pollinated flowers underwenta series of color and morphological changes including stalk elongation and ovary swelling. Therefore, stalkelongation can be considered an index of fruits set. Artificial pollination indicated that C. amoena is a highlyself-compatible and outcrossing species, but dependent on pollinators for fruit set. Based on the fieldobservations, we concluded that pollination system of C. amoena is deceptive. The fruit set in nature is notvery low (26.98% on average) compared to other deceptive orchids, which may be related to small popula-tion sizes. The number of pollinia removal is much higher than that of fruit set, indicating that there aresome degrees of pollinia wasting in C. amoena.