Study On Reproductive Characteristics And Ecological Adaptability Of Saussurea Przewalskii In Qinghai-Tibet Plateau

Qinghai-Tibet Plateau is the "modern distribution center" of the genus Saussurea where exists the unique geographical environment,complex climate,rich vegetation types and many endemic species.Because of the differences in altitude,many environmental factors were harmful to the growth of plants,such as frost,snow,gale,low temperature,low pressure,strong ultraviolet radiation,and severe soil conditions.These disadvantages could also affect the types of pollinators,quantity and scope of activities.Therefore,the combination of these factors can force alpine plants to adjust their breeding strategies to cope with reproductive stress in high altitude environments.In addition,the life cycle of many plants in the "natural and ideal adaptive ecological laboratory" of the Qinghai-Tibet Plateau have been shortened and the flowering and breeding periods have also been correspondingly shortened.However,most alpine plants,under normal conditions of life,they can ensure flowering and breeding.Therefore,in order to survive in such a stressful environment,they must have its special characteristics of floral structure,reproductive strategies and ecological adaptability mechanisms.S.przewalskii is a common and dominant species broadly distributing in the higher altitude of Qinghai-Tibet plateau.It enjoy light,but can survive in colder weather.In this article,30 populations of S.przewalskii distributed in different altitudes of the Qinghai-Tibet Plateau were selected as samples.Sampling and drying weight methods were used,floral characters,resource allocation,seed size,pollinator and another biological characteristics were analyzed,the change rule between them and altitude was demonstrated and at last the ecological adaptation mechanism of this species was discussed.The results showed:(1)Aboveground biomass(individual size),plant height,the dry weight biomass of vegetative and reproductive organs tended to decrease significantly with altitude increases.S.Przewalskii on the alpine rock reduced their individual size in order to adapt to such higher and colder stressful environment.(2)As altitude increases,there was a trade-off between mass and number of capitulum and floret(the mass gradually increases and the number graduallydecreases).The higher the altitude is,the more obvious trade-off relationship is.This showed that in the cases of the limited resources,more resources were invested in protection structure and floret display.Hence perfect flower display can attract more pollinators to pollinate in order to ensure sexual reproduction.(3)The length of sexual organs(filaments,anther,style and style branches)increased significantly,while pollen number decreased with the increase of altitude,which indicated that plants prolonged the length of sexual organs to increase pollen carrying capacity(increase anther length)and stigma contact area(extend the style branch length to improve the sensitivity of insects),in order to facilitate to make up for the decrease of the diversity and abundance of pollinating insects in high-altitude area as well as the decrease pollen number and other adverse effects on the entire pollination process factors so as to increase the chance of pollination.(4)During the flowering period,there was a significant negative correlation between vegetative allocation and altitude as well as a significant positive correlation between reproductive allocation and altitude.That is to say,S.przewalskii maximized the investment of limited available resources to the reproductive structure and used the trade-off approach to ensure survival and to increase the successful rate of reproduction.Eliminating the impact of individual size,the relationship between reproductive allocation,vegetative allocation and altitude still existed.After removing the impact of altitude,the relationship between reproductive allocation,vegetative allocation and individual size still existed.Above all,a conclusion could be drawn that both altitude and individual size could affect the allocation of plant resources balance.(5)The relative resources of S.przewalskii distributed to female and male organs decreased extremely with altitude increasing,and it also showed the tendency of partial estrogen distribution with altitude.That is probably because plants increased the stigma contact area(improve insect susceptibility)to achieve the pollen carried by pollinator to ensure the successful completion of pollination and fertilization to produce big seed.Eliminating the impact of individual size,it was found that altitude can still affect sexual distribution,and the relationship between individual size and sexual distribution did not exist after removing the influence of altitude.So there wasno dependence on individual size on the distribution of S.przewalskii.(6)The number of seeds showed a significant decrease with altitude increase,while the seed size(100-grain weight)tended to increase gradually,indicating that the S.Przewalskii produced high-quality,low-quantity seeds to improve fitness at high altitudes.Large seeds have a stronger competitive advantage and survivability in the high-cold environment.They had sufficient nutrition and strong seedlings which were more resistant to stress(anti-feeding,cold-resistance,drought-resistant,etc.).(7)Among the pollinators,bees were the most common species in the three altitude areas where the Saussurea DC.distributed.According to the frequency of visiting flowers,bees possessed the highest frequency following by flies,other insects(beetles,etc.),butterflies and ants.With the increase of altitude,the diversity,activity frequency,and abundance of pollinators were significantly reduced.