Mechanism Of Reproductive Assurance And Outcrossing Of Papaver Pavoninum,a Spring-flowering Annual Species

Reproductive assurance and outcrossing mechanisms are important areas of research in reproduction and evolutionary ecology of angiosperm.Papaver pavoninum Fisch.is a wild ornamental herbaceous annual species,which is widely distributed in the desert-steppe zone in Xinjiang of northwest China and flowers in the spring.This species is only capable of sexual reproduction,and its hermaphrodite flowers with short floral longevity are nectarless with bright color and strong floral scent,and are pollinated by insects.The flowering pattern,breeding system and pollination features of P.pavoninum were studied via field observations and controlled experiments indoor in this thesis.My aims are to explore the mechanisms of reproductive assurance and outcrossing of this species under the spring environment condition of desert-steppe zone of Xinjiang.Results can not only provide theoretical data for comprehensively revealing the adaptive mechanisms of spring flowering plants in the extreme desert environment of Xinjiang,but they also provide a theoretical basis for conservation and utilization of wild ornamental species flowering in spring.The main results are as follows:(1)Floral longevity of this species was 6.25±0.24 h,suggesting that pollination must be completed in a short time after flowering to ensure reproductive success.About 61%of the anthers in each flower are higher than or equal to the height of the stigma before pollens shed from anthers,indicating that this species is capable of autonomously self-pollination.The anthers began to disperse pollen about 2 h before flowering,and about 20%of pollen within flower had been dispersed before the flower opened completely,and some of them were deposited on the surface of stigma.Thus,this species is capable of cleistogamy.There was no significant difference in the duration of pollen viability under different temperature treatments,suggesting that the ambient temperature had no effect on pollen viability.Since both bagged without emasculation and hand self-pollination after emasculation treatments produced seeds,the species is self-incompatible and can ensure reproductive success via autonomous self-pollination.Seed-set from cross-pollination was significantly higher than that from self-pollination;thus,outcrossing is conducive to improving seed-set.Non-pollination,removal of flower parts and low temperature can prolong floral longevity.However,pollination and high temperature can shorten floral longevity.(2)Individuals of P.pavoninum have only one flower that opens each day,indicating that sexual reproduction can only be achieved through autogamy and xenogamy,thereby avoiding geitonogamy and reducing the chance of self-fertilization.Flowering mostly occurs between 05:00-13:00 each day,which is advantageous in increasing floral display and promoting outcrossing in this species with short floral longevity.The bright petals composed of red,black and peach can increase attraction to pollinators.The main volatile components from the floral organs were benzeneacetaldehyde,(E)-2-hexenal and 1-nonadecene,and the relative amount from flower organs at flowering was stamen>petal>pistil Thus,the stamens are the most likely flower part to attract pollinators,thereby promoting out-pollination.Apis mellifera is the main pollinator,and its period of peak visitation was about 1 h after flowering,which allowed xenogamy to be concentrated in a short period of time after flowering to promote outcrossing.In the unfavorable weather resulting from low temperature and wind frequently in the spring environment of the desert-steppe zone of Xinjiang,P.pavoninum,which has short floral longevity,can ensure its reproductive success via autonomous self-pollination and self-compatiblity under the condition of the lack of pollinators and/or limitation of their activities.In the favorable weather such as the sunny days and the activities of pollinators are regular,this species can promote outcrossing by concentrating flowering in the morning and by having only one flower that opens each day,large and colorful flowers,and a rich floral scent that attracts pollinator visitation within a short period of time after flower opening.