Reproductive Traits Of Saxifraga Signata In The Hengduan Mountains

Alpine environment is considered among one of the harshest on the earth.Unpredictable weathers and scarce pollinators of limited pollination service present great challenges for life here.However,the elevation lift in alpine regions allows the ecological factors to change rapidly within a short spatial distance,which makes the vegetation landscape change rapidly from the foot of mountains to the top.Therefore,the alpine environment has become a natural laboratory for phytogeographical and ecological research.As the most typical north-south mountain in southwest China,the Hengduan Mountains cover a vast area and host unpredictable alpine weathers and diverse vegetation types,all of which make this area an international biodiversity distribution center.Reproduction is the most important life activity of alpine plants.Their reproductive traits and reproductive resource strategies are affected by the environment.The interaction between plants' reproductive traits and alpine environment deserves deeper exploration,such as gender presentation,mating system,insect visiting pattern,floral behavior,pollination,and seed germination.In this study,Saxifraga signata,a typical herb in the Hengduan Mountains of Southwest China,was used as the material,to investigate the influence of alpine environment on the reproductive characteristics of S.signata.Specifically,I analyzed the factors regulating stamen movements of S.signata by natural sampling and artificial control.Furthermore,I observed the process of flowering and pollination in the natural populations of S.signata,measured the reproductive investment of male and female gametes,and conducted the germination experiments of seeds under different cold treatments,in order to reveal the adaptative features of the entire reproductive process of S.signata.The main findings are as follows:1.Flowering and pollination characteristics of S.signata-The flowering period of S.signata is from July to August based on observations at its natural populations.The flowering process can be divided into three phases: preparation phase,male phase and female phase.The male phase lasts 5-7 days,and the female phase lasts 2-3 days.At the intra-flower level,sexual function is completely separated by protandry.However,at the inflorescence level,sexual function is regulated by incomplete dichogamy,and there is a possibility of overlapping period of male and female function.Flies were the predominant visitors of S.signata,among which blow flies and tachinid flies were the main pollinators.Flies showed strong preference over male phase flowers.Supplemental pollination experiments revealed that the reproduction of S.signata was pollen limited.Selfing experiment proved self-compatibility in S.signata,which was thought to be an evolutionary product in face of inadequate pollination service in alpine environments,providing reproductive assurance for S.signata to a certain extent.Pollinator visits made geitonogamous selfing possible,but the degree of dichogamy maintained this probability at 10-20%,avoiding severe inbreeding depression and sexual interference.2.One by one stamen movement of S.signata-Based on the observation of the flowering dynamics at natural populations,this study found that the stamen movement of S.signata presented a "one by one" pattern,that is,the five stamens between the petals move first in sequence.After they are completed,the remaining five stamens close to the petals continue to move,and finally ten stamens complete an ascent and a return in sequence The amount of pollen at the anther level of S.signata also showed distinctive differences,that is,the amount of pollen per anther increased linearly with the ascending sequence,indicating that plants tend to limit the resource allocation per anther in the early stage of male phase,and gradually increase in the middle and late stages.This type of resource investment may help improve the efficiency of pollen export.In addition,the artificial manipulation demonstrated the dynamic response of stamen movements of S.signata to weather conditions and pollination intensity.When the weather was fine or natural pollinators visited frequently,the number of stamens displayed per day increased significantly,and the duration of male phase was shortened accordingly.This dynamic response to pollination environment may increase mating opportunities of male functions and improve the effectiveness of pollen transfer.3.Seed germination-The germination rate of S.signata was moderate,and cold stratification had little effect on germination: In this study,we found that the average germination rate of four cold treatments of S.signata was only 39%,and cold stratification was not a necessary procedure for seed germination in S.signata.In conclusion,the reproductive process S.signata shows a highly flexible response to unpredictable weathers and limited pollination service in the Hengduan Mountains of southwest China,revealing its endurance and adaptation under the harsh environmental stress in high mountains.Meanwhile,this study focuses on the factors influencing the one by one stamen movement of S.signata,which fully demonstrates the dynamic reproductive strategy of S.signata.Considering the trends of global change,this research helps understand the interactions between alpine plants and their changing environment,and provides an empirical study for practical evaluation and prediction on reproductive capacity of alpine plants.