| For a long time,reproduction,as the core of evolution,has been widely concerned by biologists.As the highest altitude and largest plateau in the world,the Qinghai-Tibet Plateau(QTP)has the characteristics of low temperature,low pressure,strong wind,heavy rain,snow cover,strong ultraviolet radiation,but the growth and reproduction of plants in this area show strong adaptability to the harsh environment.The growth and reproduction of plants in this area show strong adaptability to the harsh environment,which can not only adapt to the selection of all kinds of non-pollinating organisms,but also show a high success rate of reproduction in the harsh alpine environment.The QTP covers correspondingly wide geological and climatic gradients,and thus hosts abundant plant diversity.Due to its extreme environmental and biological diversity,the QTP is also an ideal region for studying the mechanism of plant ecological adaptation and reproduction.In order to study the optimal allocation of reproductive resources in the inflorescence of alpine plants,the effects of non-pollinator on pollination and reproduction of alpine plants,and the significance of abiotic factors on adaptive evolution of alpine plants.In this paper,three kinds of flowering plants in alpine meadows on the QTP,which have been under the selection pressure of pollinators,nectar robbers and abiotic environment for a long time,were used as experimental materials to study the reproductive strategy and adaptive mechanism of alpine plants.This study can not only help us to understand the reproductive and evolutionary strategies of alpine plants,but also provide an important theoretical basis for the protection of alpine plant diversity and the effective utilization of biological resources.The main contents are as follows:(1)Floral sex allocation and reproductive success within inflorescences of Delphinium trichophorum.(2)Effects of nectar robbing on geitonogamy and inbreeding depression of Gentiana straminea.(3)Adaptive significance of the hairy corona structure to Comastoma pulmonarium.The main results are as follows:1.Floral sex allocation and reproductive success within inflorescences of Delphinium trichophorumIntra-inflorescence variation in floral sex allocation and reproductive success are common in hermaphroditic plants,and several non-exclusive hypotheses,including resource competition,architectural effect and the mating environment,have been formulated to explain this phenomenon.In order to investigate the optimal allocation mode of male and female reproductive resources between different positions in the inflorescence,through comparison of floral and seed traits,the floral sex allocation and female reproductive success within inflorescences of Delphinium trichophorum(Ranunculaceae),a typical alpine plant was investigated.Observation of pollinator movements,artificial flower-removal experiment,and hand-supplemental pollination were also used to investigate the effects of resource competition and mating environment on allocation of reproductive resource in the inflorescence.The major results are as follows:(1)From bottom to upper positions of inflorescence,stamen number,stamen mass/pistil mass,pollen number and pollen/ovule ratio all increased significantly,while pistil mass and ovule number declined gradually,thus upper flowers performed male-biased function.Seed set ratio of upper flowers were significantly lower than bottom and intermediate flowers.The number and mass of mature seed per fruit decreased significantly with the increase of flower position,indicating greater female reproductive success of bottom flowers.(2)The flower-removal experiment improved single seed mass of the remaining fruits,but did not increased the number of mature seeds per fruit.There were no differences of seed set ratio among positions after hand-supplemental pollination of upper flowers,which suggested that the position-dependent pattern of seed reproduction within inflorescences was attribute to pollen limitation rather than resource competition.(3)The protandry of Delphinium trichophorum and the directional visiting behaviors(from bottom to upper)of pollinator Bombus sushikini led to variations of mating environment within inflorescences.On the basis of the above results,we concluded that intra-inflorescence variation in floral sex allocation and reproductive success of D.trichophorum were results of adaptation to mating environment and this strategy was of great importance to optimize the male and female fitness for the species.2.Effects of nectar robbing on geitonogamy and inbreeding depression of Gentiana stramineaIn the relationship between animals and plants,nectar robbing is an abnormal flower-visiting behavior that is different from that of ordinary pollinators.It usually changes the traits and reward of flowers,which has an important impact on the pollination mechanism and reproductive strategy of alpine plants.Gentiana straminea(Ranunculaceae),as the object of study,three treatments of artificial nectar robbing,stop nectar robbing and control were used to compare the effects of nectar robbing on flower visiting behavior,flower visiting efficiency,total pollen removal and seed setting rate of legal pollinators.Four treatments of different robbing treatments(netted and robbed)and pollination modes(selfing and outcrossing)were adopted,and the obtained seeds were used to carry out further common-garden experiments to study the degree of inbreeding depression in several life history stages under the conditions of nectar robbing and stop nectar robbing.Based on the statistics of plant density,nectar robbing frequency,flowering pattern and nectar traits of different populations,and through the experiment of common-garden,the effect of nectar robbing frequency of different populations on the evolution of nectar traits was discussed.The main results are as follows:(1)Nectar robbers indirectly weakened the degree of geitonogamy of plants by affecting the flower-visiting behavior of legitimate pollinator,such as the number of flower visits per plant,the visiting time per flower and the flight distance between plants.(2)By consuming nectar resources,nectar robbers cause changes in resource allocation of Gentiana straminea,thus affecting the degree of inbreeding depression in the later stage of their life cycle.(3)There are significant differences in the frequency of nectar robbing among populations at different elevations.Nectar robbers may act as a selection pressure on the evolution of nectar traits,resulting in different nectar secretion among different populations.The above results show that nectar robbing plays an important role in the cost and corresponding compensation mechanism of cross-pollination in alpine plants,and reveals the important role of nectar robbing in the evolution of flower traits and environmental adaptation of alpine plants.3.Adaptive significance of the hairy corona to an alpine plant Comastoma pulmonariumRainwater,which occurs frequently in alpine areas,will wash away part of the pollen and reduce the ability of pollen germination,and strong ultraviolet radiation will also reduce the vitality of pollen.Plants in this area often evolve a special flower structure in order to avoid adverse environmental factors.In this paper,the hairy corona of alpine plant Comastoma pulmonarium was studied to explore the evolutionary and adaptive significance of this distinctive floral structure in the extreme alpine environment and its effects on plant reproductive fitness.By comparing the natural state with the flowers with artificial removal of accessory crown,the main results are as follows:(1)The hairy crown can effectively reduce the scouring of pollen quantity by rain-wash,maintain viability of pollen grains in front of rain immersion and intense solar radiation.(2)The hairy crown increased the fertilization rate,but had no significant effect on seed weight and seed germination rate.This study indicates the hairy coronal structure of Comastoma pulmonarium has adaptive strategy to both male and female reproductive success in the harsh environment of alpine regions,rainy and strong radiation,and further confirms selection on the flower morphology of alpine plants by abiotic factors. |
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