In hermaphroditic plants,female reproductive success often varies among different positions within an inflorescence. However,few studies have evaluated the relative importance of underlying causes such as pollen limitation,resource limitation or architectural effect,and few have compared male allocation. During a 2-year investigation,we found that female reproductive success of an acropetally flowering species,Corydalis remota Fisch. ex Maxim. var. lineariloba Maxim. was significantly lower in the upper late developing flowers when compared with the lower early flowers. Supplementation with outcross pollen did not improve female reproductive success of the upper flowers,while removal of the lower developing fruits significantly increased female reproductive success of the upper flowers in both years,evidencing resource limitation of the upper flowers. Female production in upper flowers was greatly improved by simultaneous pollen supplementation of the upper flowers and removal of the lower fruits,suggesting that,when resources are abundant,pollen may limit the female reproductive success of the upper flowers. The less seed mass in the upper flowers didn't increase in all treatments due to architecture. In the upper flowers,ovule production was significantly lower and the pollen :ovule ratio was significantly higher. These results suggest that male-biased sex allocation in the upper flowers may lead to increased male reproductive success,whereas the lower flowers have higher female reproductive success.
Theory predicts that cosexual plants should adjust their resource investment in male and female functions according to their size if female and male fitness are differentially affected by size. However, few empirical studies have been carried out at both the flowering and fruiting stages to adequately address size-dependent sex allocation in cosexual plants. In this paper, we investigated resource investment between female and male reproduction, and their size-dependence in a perennial andromonoecious herb, Veratrum nigrum L. We sampled 192 flowering plants, estimated their standardized phenotypic gender, and assessed the resource investment in male and female functions in terms of absolute dry biomass. At the flowering stage, male investment increased with plant size more rapidly than female investment, and the standardized phenotypic femaleness (ranging from 0.267 to 0.776) was negatively correlated with plant size. By contrast, female biased allocation was found at the fruiting stage, although both flower biomass and fruit biomass were positively correlated with plant size. We propose that increased maleness with plant size at the flowering stage may represent an adaptive strategy for andromonoecious plants, because male flowers promote both male and female fertility by increasing pollinator attraction without aggravating pollen discounting.
