Intra-inflorescence Variation Of Floral Traits And Sex Allocation In Camptotheca Acuminata Decne

The variation of floral phenotypic traits and sex allocation among different position within inflorescence is a very common phenomenon in Angiosperms. The common variation pattern is that the number and size of reproductive structure decreasing successively from early flower to later flower within the same inflorescence with sequential blooming, and the resources allocation of later flower tend to male. So far in the previous research, several factors have been proposed to explain the variation in floral trait and sex allocation among position within inflorescences, such as resources competition, architectural effects, pollinator directionality, adaptive hypothesis etc. Camptotheca acuminata (Nyssaceae) a endemic species in china, which is widely distributed in Yangtze River Basin and the provinces of Southwest China. The study of distribution, biological characteristics, medicinal value, reproductive biology, ecological benefit, introduction and cultivation in C. acuminata had been reported. But intra-inflorescence sex expression and allocation of C. acuminata has been not studied until now. C. acuminata’s cyme is composed of1-13(generally4/5)capitula. Within the cyme of C. acuminata, the early capitula are composed of hermaphrodite flowers, with large capitulum in diameter and high fruit set; the late capitula’s sex expression tend to male, with small capitulum in diameter and low fruit set or no fruit. There are significant variation in floral traits and resource allocation among different position of capitulums within inflorescence. The main questions we addressed are:(1)Measure intra-inflorescence variation of floral traits and sex allocation among different position in natural conditions.(2)Pollen limitations were tested by comparing fruit set and infructescence mass between natural pollination group and supplementary hand-pollinated group.(3)We expected part of capitula removal can increase the available resources within inflorescence. The influence of architectural effects and resource competition to floral traits and sex allocation of different position within inflorescence for C. acuminata were measured separately by comparing capitula’s floral and fruit traits in equivalent position of different treatment groups.(1)In natural conditions, there are significant differences in the diameters of capitulum and corolla, flower number, length of short stamen and style, ovary size (diameters and dry-weight), fruit set rate and infructescence mass among different positon within the cyme of C. acuminata. (2)The fruit set and infructescence mass not changed significantly after supplementary hand-pollinated, thus the limitations of pollen was not found.(3)After removing part of the capitula, the pollen grains per flower in the remaining capitula increase significantly, while the diameters of corolla and the length of short stamen change significantly, and the differences between position disappears. After removing part of the capitula, the differences between position in style length and ovary size (diameters and dry-weight) were ameliorated, but not eliminated completely. However, the differences in fruit set and infructescence mass remained unchanged regardless of the plant’s resource status. This suggests that resource constraints rather than architectural effects have stronger influence on the nongynoecial characters for flowering season such as:the diameters of corolla, the length of short stamen and the pollen grains per flower; while architectural effects play a dominant role on fruit set and infructescence mass. But the gynoecial characters for flowering season such as style length and ovary size (diameters and dry-weight) were affected by both resources competition and architectural effects.In conclusion, The influence strength of resources competition and architectural effects to diverse floral traits of inflorescence in C. acuminata was different. The evolution of inflorescence andromonoecy in C. acuminata may be the result of adaptation to specific resources and reproduction competition.