雄全同株植物簇花芹花期性别分配与开花式样

Floral sex allocation and flowering pattern in the andromonocious Soranthus meyeri (Apiaceae)

簇花芹(Soranthusmeyeri)是古尔班通古特沙漠中常见的、具雄全同株性系统的伞形科多年生早春短命植物。该文对簇花芹花期性比(两性花数/总花数)与植株大小的关系及其开花式样进行了研究,重点对花期大小依赖的性别资源分配进行了讨论。结果表明:2006–2008年簇花芹群体水平的性比分别为0.69±0.03、0.62±0.03和0.69±0.02,彼此间无显著差异(p>0.05),表明其性比是相对稳定的,可能受遗传因素的控制。雄花生物量与花粉量均比两性花的小,说明产生雄花比产生两性花所需资源少。一级复伞形花序比二级复伞形花序具有较多的两性花,说明前者易从植株上获得资源用于增加雌性适合度;而后者产生较多的雄花以避免在雌性功能上资源投入的浪费,增大花展示以吸引更多传粉者来增加花粉输出总量,提高其整体适合度。植株水平的性比与地上营养器官的生物量间呈正相关关系,说明较大个体对雌性功能的投资较大,雌性繁殖成功受资源限制。复伞形花序内各伞形花序几乎同时向心开放,且所有两性花及花序均为雄性先熟,雌雄阶段完全分离,但一级复伞形花序比二级复伞形花序早开放约5天,彼此开花重叠期约为1天。这些特征对于一级复伞形花序进行异株异花授粉以及植株内不同级别花序间的同株异花传粉、避免雌雄功能间的干扰具有重要意义。

Aims Andromonoecy, the presence of both staminate and hermaphrodite flowers on the same individual, was observed in Soranthus meyeri, a common early spring ephemeral perennial in the Guerbantonggut Desert of Northwest China. The relationships between sex ratio （number of hermaphrodite flowers/total number of flowers） and plant size and the flowering pattern of both staminate and hermaphroditic flowers of this species were studied to determine size-dependent sex allocation and flowering pattern. Methods The study was conducted from May to June in 2006-2008. Morphology, number and dry mass of both staminate and hermaphroditic flowers were determined. Position of the two types of flowers and their flowering pattern at the level of the flower, umbel and individual were recorded. Individual biomass was determined, and the relationship between number of staminate and of hermaphroditic flowers and plant size was analyzed. Important findings The sex ratio within a population of S. meyeri was 0.69 ± 0.03, 0.62 ± 0.03 and 0.69 ± 0.02 in 2006, 2007 and 2008, respectively, and there were no significant differences among the years. This indicates that the sex ratio of this species is stable and possibly controlled by genetics. Staminate flowers produced less pollen, and their biomass was smaller than that of hermaphrodite flowers, suggesting that staminate flowers were less expensive to produce. Primary umbels produced more hermaphrodite flowers than secondary umbels, indicating that the primary umbels are capable of obtaining more resources from the mother plant and increase female fitness. Resources saved by not producing hermaphroditic flowers in secondary umbels could be reallocated to produce more staminate flowers, thus increasing floral display to attract more pollinators as well as enhancing pollen export and overall fitness. The sex ratio per plant was significantly, positively correlated with aboveground vegetative organ biomass, and large plants allocated more to the female function than small plants. Thus, female reproductive success is limited by availability of resources. Flowers in the primary umbel bloom first, followed by those in the secondary umbel five days later. All umbels of the same order flower simultaneously, and all flowers within an umbel open centripetally. Separation of male and female phases through protandry is complete both within hermaphrodite flowers and within umbels, thus avoiding interference between the male and female function and promoting xenogamy. However, there is an overlap of about one day between umbels of consecutive orders, which can provide conditions for geitonogamy.