MOE Key Laboratory of Arid and Grassland Ecology, Lanzhou University, Lanzhou 730000, China.
J Plant Res. 2012 Jul;125(4):527-38. doi: 10.1007/s10265-011-0466-2. Epub 2012 Jan 24.
Studies of diclinous species have showed that floral sex allocation and female reproductive success were quite variable within inflorescences. However, little attention has been paid to gynomonoecious species, in which individuals produce both female and bisexual flowers. The purpose of this study was to investigate the variations in reproductive patterns at different capitulum positions within racemiform synflorescence in Ligularia virgaurea, and to determine selective mechanisms of variations in reproductive patterns. We conducted observational and experimental studies in natural populations of the gynomonoecious composite L. virgaurea. Floral sex allocation, seed production and pre-dispersal seed predation were quantified in the field. The results showed several patterns of variation from top to bottom capitula, including an increase in bisexual flowers and flower number per capitulum, but a decrease in seed set and size. Removing earlier capitula during bud stage did not change floral sex allocation in later capitula. And no effect was found on seed set under supplemental pollination. Thus, although it has been reported many times in previous studies, the variation of floral sex allocation in L. virgaurea may not result from architectural effect or mating environment, and the variation of seed production could not be fully explained by pollination success. Additionally, our results showed that L. virgaurea was susceptible to high levels of bisexual biased predation, which was greater for top capitula. We therefore suggest that these variations may help to enhance reproductive success of L. virgaurea in the face of bisexual-biased seed predation.
雌雄同株植物的个体既产生雌花又产生两性花。雌雄同株植物的研究表明，花序内的花性别分配和雌性生殖成功具有相当大的变异性。然而，人们对雌雄同株植物的关注较少，在雌雄同株植物中，个体既产生雌花又产生两性花。本研究旨在调查在异花合轴头状花序中，不同头状花序位置的生殖模式的变化，并确定生殖模式变化的选择机制。我们在雌雄同株的复合种千里光（Ligularia virgaurea）的自然种群中进行了观察和实验研究。在野外量化了花的性别分配、种子产量和预散布种子捕食。结果表明，从顶部到头状花序的下部有几种变化模式，包括两性花和每个头状花序的花数增加，但结实率和大小下降。在芽期去除早期头状花序不会改变后期头状花序的花性别分配。在补充授粉下，对结实率没有影响。因此，尽管在以前的研究中多次报道过，但千里光花的性别分配的变化可能不是由于结构效应或交配环境引起的，并且种子生产的变化不能完全用授粉成功来解释。此外，我们的结果表明，千里光容易受到高水平的两性偏向捕食的影响，顶部头状花序的两性偏向捕食更大。因此，我们认为这些变化可能有助于提高千里光在面对两性偏向种子捕食时的生殖成功。
