Study On The Reproductive Strategy Of Genus Saussurea In Eastern Margin Of The Qinghai-Tibet Plateau

Saussurea DC was a large genus of the composite family, mainly containing five subgenera: Subgen.Eriocorrne, Subgen.Amphilaen, Subgen.Theodorea, Subgen.Florovia and Subgen.Saussurea, the most of Saussurea were annual or biennial herbage 、perennial herb, even a semi-shrub. Currently, there are total of more than 400 species in the world, mainly in Asia and Europe region. There are about 264 species in China, mainly in the Hengduan Mountains to the Qinghai-Tibet Plateau area, always be the common component of alpine meadow plant communities. According to statistics, there are 36 kinds species of Saussurea in Gannan Tibetan Autonomous Prefectur. Saussurea distributes in a larger span of altitude, response of elevation changes,different species takes varied reproductive strategies. However, previous studies in reproductive strategies of Saussurea, is more focused on a single aspect of that, lack of comprehensive analysis for reproductive strategy around the whole process of seed generation. Therefore, this paper made the eastern of Gannan Tibetan Autonomous Prefecture as the main study area, collecting Saussurea plant specimens and seeds annually from August to October in 2012—2014 in the area(Samples were collected, try to keep complete plant, In laboratory weighing various parts of the drying plant, the plant’s dry weight data obtained; clean up debris after seed collection, it is stored for use), we researched Saussurea plants of reproductive allocation adjustments in different elevation, and seed properties(seed size, seed surface ornamentation, the chemical composition of the seed) and the germination rate of seeds. Do the comprehensive research and analysis, in order to interpret more about Saussurea reproductive strategies when living environment changes.The main research results are as follows:1.With the increase of altitude, the individual plants decreased significantly, negatively correlated between plant size and altitude, smaller individual plants showed the better adaptability.2. With the increase of altitude, the absolute resources input on the reproductive organs is decreased, the reason is to avoid decreases the resources of vegetative organs and then reduce the survival rate, and the same time, to avoid the waste of resources.3. Saussurea ensure the investment of resources of the tubular, suggesting that the tubular flower contains pistil and stamen, is the core part of the reproductive organs. In high altitude,the more resources investment of tubular flower increase the rate of successful pollination.4. By studying sex allocation of Saussurea, we did not get a change trend, in a high altitude, partial female allocation and partial male allocations all exist, different species takes varied reproductive strategies.5. Throuth the research of relationship between Saussurea seed size and altitude, we do not have a unified conclusion. With the increase of altitude, some species of the genus plants will choose the large seed to produce a strong competition seeding, some species will choose the large number of small seeds to overcome the high altitude stress.The reproductive strategies was different because of different species.6. The weight of seeds in a capitulum is highly correlated with the 100 seeds weight. It can be inferred that the number of seeds in a capitulum is not changed too more, and the number of the seeds is relatively stable.7. In the study found the content of C in seeds was relatively stable, while the content of P and N increased with the decrease size of seed. Therefore, because of its high N and P content, the seed has a high level of protein and ribosome to support the early growth of the seedling, to overcome the harsh environment.8. From low to high elevations, Saussurea seed surface ornamentation have a tendency to complicate evolution. Seed surface stripe width(SW) and distance between stripes(DBS) decreased while sulcus depth(SD) increased. The seeds of Saussurea changes its surface ornamentation of seed coat to absorb more water and nutrients, and in high altitude receive more sunlight, to promote seedling sprouting.9. Seed size and seed germination index was positively correlated, which means that the more smaller the seed is, the faster the seed germination. Because of the large number and the faster germination rate, small seed has stronger ability to colonize, to make up for its smaller inferior seedlings.10. The seed germination time showed a negative correlation with altitude, at higher altitude seed germination in earlier time. In a high altitude, the environment is harsh, effective plant germination time is shorter, compared to low altitude, seed germination conditions is worse, so under the same conditions,the seed from the higher altitude,its germination rate is higher than the seed from a lower altitude,the advantage in germination rate ensures the completion of the life cycle.