Study On The Response Of The Reproductive Traits Of The Five Species Of Saussurea DC With Altitude In Qinghai-Tibet Plateau

Reproduction is a critical issue in the study of plant evolution,and since there is a limit to the amount of resources available at each stage of plant's development,plants must seek an optimal allocation scheme for resources in terms of growth,survival and reproduction,in order to achieve the reproductive success.The resource allocation and reproductive strategies have certain significance for interpreting and predicting vegetation structure changes and zone shifts during global change.Growth environment conditions such as altitude have a great influence on the individual size of plants and reproductive strategies.Plants growing at different altitudes may adopt relatively different reproductive strategies.In the Arctic or high altitude areas,insect-borne pollination success is often limited by the low frequency of pollinators,so they must improve self-pollination,apomixis and vegetative propagation;and obligate or apparently outcrossing species will take an increase the means by which pollinators attract structural investment.The unique geographical environment and complex climatic conditions of the Qinghai-Tibet Plateau have enriched the abundant vegetation types and many endemic species,while the harsh environmental factors such as frost,snow,gale,low temperature,low pressure and strong ultraviolet radiation,etc.Then how do plants arrange their breeding strategies to cope with the reproductive pressures in high-altitude areas,attracting the attention of many reproductive and evolutionary ecologists.In view of this,we study the five species of alpine plant(S.leontodontoides,S.katochaete,S.stella,S.iodostegia,S.tangutica)widely distributing in Qinghai and Tibet,analyze the floral characteristics,seed characteristics and reproductive allocation of different altitude populations and discuss the relationship between floral characteristics,seed characteristics,reproductive distribution and individual size of different altitude populations.So as to reveal the internal rule of the influence of altitude on plant reproductive strategies.The results show:(1)Altitude has an important influence on the floral characteristics and seed characteristics of the five species of the Saussurea genus,but the altitude has differenteffects on the different reproductive characteristics of the Saussurea genus.Compared with low altitude population,capitulum biomass,the weight of the tubular florets,hundred kernels weight and seed weight of high altitude population gradually increased;while the number of tubular florets,the number of pollen and the number of seeds gradually decreased.As the altitude increases,the pollinator's activity frequency decreases.In order to complete the reproduction of Saussurea genus,the plant's reproductive success is prompted by increasing the investment in the flower structure.In the alpine environment,the larger seeds have stronger competitive advantage and survivability,and the seedlings are more resistant to stress(such as anti-food,anti-cold,anti-drought,etc).(2)There are significant differences in the reproductive invest and reproductive allocation of the high and low altitude populations of the five species of Saussurea genus.In other word,the altitude has an important influence on the reproductive strategies of Saussurea genus.Compared with low altitude population,the plant's reproductive invest of high altitude population gradually decreases,but the reproductive allocation gradually increases.It shows that in the case of limited resources in high-altitude areas,the amount of resources that plants can use is reduced,so the amount of resources allocated to each organ is also shrinking.In a limited resource environment,plants put more resources into the “ flower ” structure,as the altitude increases,the plant's input to reproductive resources(absolute capital)is decreasing,while the investment in reproductive organ resources(relative capital)is increasing.(3)The floral characteristics,seed characteristics,reproductive invest and reproductive allocation of Saussurea genus have strong individual size dependence,and the different reproductive characteristics of the same species have different dependence on individual size,but the same dependence of reproductive characteristics on individual size also varies from species to species.Individual size dependent reproductive characteristics are the plasticity of plants to the environment.In other word,the Saussurea genus adapts to changes in altitude gradients by adjusting the allometric relationship between individual size and reproductive characteristics.(4)By using the residual method to control the size of individual plants,there are trade-offs between the number of tubular florets-the weight of tubular florets(flower size)and the number of seeds-hundred kernels weight(seed size).By reducing the number of flowers and the number of seeds,plants produce “ big and excellent ” flowers and seeds to adapt to the environment and improve their fitness.