露蕊乌头（Aconitum gymnandrum Maxim）花序内位置依赖的性分配

植物会采取什么样的繁殖对策来保障它的雌性和雄性繁殖成功,特别是那些生活在高寒地区的植物,已经引起了很多学者的关注.通过野外盆栽试验对青藏高原东部高寒草甸上的常见物种露蕊乌头(Aconitum gymnandrum Maxim)花序内的性分配模式进行了研究,发现同其它顶向式(从花序基部到顶部)开花的植物一样,随着花从基部到顶部的次序,露蕊乌头的心皮数、雌蕊重、种子数和种子重/果实减少;而花药数,花粉数/胚珠数以及雄蕊重/雌蕊重增大,顶部花表现出偏雄的性分配.结籽率在不同的位置间没有显著差异,不受花粉数量的限制;去花实验没有增加剩余部位花的种子数,只是增加了种子大小,这是花序内不可避免的位置效应导致了花序内位置依赖的性分配模式.

Position-dependent sex allocation within inflorescence of Aconitum gymnandrum Maxim

The question of which resource allocation patterns will be selected to ensure male and female reproductive success has attracted many researchers, especially in reference to plants of alpine environments. This study investigated the pattern of reproductive allocation within inflorescences of Aconitum gymnandrum Maxim, a common species of the Qinghai-Tibet Plateau, and experimentally explored the potential mechanism underlying this pattern.
Data on floral allocation and seed production in bottom, middle, and top flowers in racemes of A. gymnandrum were gathered in a variety of sub-alpine and alpine meadows, and their maternal plants were collected. A flower-removal experiment also was performed, to determine whether allocation was affected by within-raceme competition. These data were analyzed with repeated-measures analysis of variance and two-way analysis of variance.
Results showed that there was a marked decline in carpel number, female mass, seed number, and seed mass per fruit with flowering sequence within a raceme, while anther number, male/female mass ratio and pollen/ovule ratio increased. Floral sex allocation was male-biased in top flowers, while seed set was constant among positions. Variation in the amount of pollen received cannot explain the observed results, and the flower-removal experiment did not improve the seed set of the remaining flowers, indicating that an unavoidable architectural effect has led to the position-dependent pattern of sex allocation with raceme.