【摘要】 在北京东灵山地区 ,沿一定海拔梯度 ,对藜芦 (Veratrumnigrum)这一雄花两性花同株的多年生草本植物的繁殖特征进行了初步研究。结果表明 :藜芦开花植株的生物量显著大于未开花植株的生物量。藜芦开花植株大小存在最小临界值 ,总种群的最小临界值为 2 .61g ,不同种群的繁殖临界值存在一定的差异。根据花粉 胚珠比 (Pol len ovuleratio ,P O比 )推测 ,藜芦应属于以异交为主的混合交配系统。雄花的大小与生物量都比两性花小 ,而且其开放时间也晚于两性花 ,但二者的花粉生产量却没有显著差异。这种现象与人们针对雄花两性花同株植物的雄花功能所提出的最优资源分配假说 (Optimalresourceallocationhypothesis)是一致的更多还原

【Abstract】 A preliminary study was conducted on the reproductive features of d ifferent populations of Veratrum nigrum along an altitudinal gradient in Don gling Mountains, Beijing. V. nigrum is a perennial, andromonoecious herb. We u se P/O ratio (Pollen/ovule ratio) as an estimate of the level of outcrossing. Re source allocation was measured by means of dry weights. We found that the flowering individuals within a population were larger than the non_flowering individuals. The resource allocated to reproduction was strongly correlated with that allocated to vegetative growth. Individuals of V. n igrum would not produce flowers and fruits until a threshold size was reached, whi ch ranged from 1.11 g to 3.98 g in different populations. The minimum size showe d no trend along the altitudinal gradient, indicating that an invariable minimum v egetative biomass for the species might exist. Pooled together, a minimum size o f 2.61 g for reproduction followed from the regression line. Above the threshold there existed a relatively simple linear relationship between vegetative and rep roductive biomass. Population density decreased firstly and then increased along altitudinal gradient, but it seemed that density is not related, in a straightf orward way, to the reproductive features of V. nigrum in the study region. Many workers had shown that the flowers of self_incompatible and other xenogamou s taxa produced more pollen grains than closely related self_compatible and/or a utogamous taxa, while the number of ovules per ovary was rather conservative, in contrast to other floral characteristics. In this article, we estimated P/O rat ios both at the level of a hermaphrodite flower and at the level of an individua l (including male flowers). We found that the difference in mean hermaphrodite f lower P/O ratios among populations was not significant. Hermaphrodite flowers ha d P/O ratios from 799 to 1 090. However, the difference in mean individual P/O r a tios among populations was strongly significant. The lowest individual P/O ratio was 1 601 and the highest was 4 146. According to the correlation between P/O r at ios and mating systems established by Cruden, V. nigrum in Dongling Mo unta ins was facultatively xenogamous. There was a positive correlation between the P /O ratios of hermaphrodite flower and the ratios of reproductive to vegetative b iomass. Hermaphrodite flowers are mainly distributed at the tip raceme of the panicle, w hile males are at the lateral racemes. Sometimes, flowers near the base of the l ateral racemes are hermaphrodite. Hermaphrodite flowers bloom earlier than male flowers, and the two flower types differed in dry weights. Hermaphrodite flowers averaged 5.10×10 -3 g while male flowers averaged 4.04×10 -3 g. Herma phrodite flo wers were on average 26% more massive than male flowers. Flower diameter was (1. 42±0.01) cm for hermaphrodite flowers and (1.24±0.01) cm for males. Hermaphrod ite fl owers were on average 15% larger than male flowers. However, the pollen producti on of hermaphrodite and male flowers remained almost the same. The results docum ented here suggest male flowers of V. nigrum provide resource savings to t he plant compared to hermaphrodite flowers. Since male flowers have lower resour ce use for equal pollen production in comparison to hermaphrodite flowers, they are more efficient at male function than hermaphrodite flowers. These results le nd support to the optimal resource allocation hypothesis for the function of mal e flowers within an andromonoecious sexual system.更多还原