The Study On Seed Germination And Seedling Growth Characters Of Ligularia Virgaurea

Ligularia virgaurea is one of a few species of the genus distributed in the higher altitude region. Recently, the Alpine Meadow has seriously deteriorated and Ligularia virgaurea has become one of the predominant toxic weeds in Eastern Tibet. However, no effective prevention has been suggested. In recent years few studies have been done on the sexal-reproduce, seed germination and seedling growth of L. virgaurea, Therefore, to grasp the life history strategy of L.virgaurea is the main purpose of the present study, and it will provide theoretical evidence for management of grassland by discovering the life history strategies of plant adapted to such a special environment in Qinghai-Tibet plateau. Through observation in field and lab and data analysis during two year. The conclusions are summarized as follow:(1)Mature seeds of L .virgaurea may germinate under different light conditions, the germination rate and percentage of seeds stored for one month increase and mean germination time decrease with increasing temperature. However, under low temperature and shaded condition, the germination percentage increases with storage time increasing. The longer storage time, the lower germination percentage. There is a significantly positive relation between germination rate and storage time. Mean germination time of seeds stored for twelve months is shorter than that stored for one month.(2)There is a prominent effect of L .virgaurea seed size on seedling's emergence. Seedling emergence percentage is larger for the heavier seed than smaller seed, and mean emergence time is shorter. There is no relation between light and emergence percentage, consistent with experimental results. But, there are significant effects of light on mean emergence time. Under the unshaded condition larger seeds emerge rapidly. As light rays are weakening, mean emergence time has extended.(3)There is a significant effect of light on seedling growth. Under the unshaded conditions, seedlings from small seeds have higher relative growth rates (RGR) than do seedlings from large seeds. Under shaded conditions, seedlings from both large seeds and small seeds show a increasing tend in RGR. By contrast, seedlings from small seeds have significantly decreased. There is not a significant relation between seed size and seedling's RGR. Larger seedling has faster maximum relative growth rate, suggesting that although the relative growth rate is negatively related with the seed dry mass, the larger seedling has the advantages to get to a larger maximum biomass correspondent with its capability of up-ground competition and early establishment.(4)There is a noticeable effect of light on the morphological features of one-year old seedlings and two-year old seedlings. Under the unshaded conditions, L .virgaurea exhibits largest total leaf area, shorter petiole and excessive roots and its leaves form small angles with petioles, and extend in parallel to the earth surface. Under shaded conditions, L .virgaurea shows smaller total leaf area, prolonged petiole, thinner and larger leaves And its leaves have larger angles from petioles and grow upright. Seedlings from large seeds and small seeds show the same tendency. (5)There is a marked influence of light on biomass accumulation and allocation of L .virgaurea seedlings. Under unshaded conditions, seedling biomass and seed size have a positive relation. Seedlings from heavier seeds are larger than from small seeds. With seedling growing, L .virgaurea plants r/s increases significantly, and allocates more carbohydrate to roots. With the light rays decreasing, seedlings from big and light seeds will allocate more nutrition to leaf growth. By contrast, seedlings from small seeds have significantly increased. Positive relation exists between leaf area and seedling biomass for seedlings. Big individuals of L .virgaurea have numerous structures of photosynthesis. As a result, these increase ability of seedling in colonization and contest.(6)At the beginning of the second growth season, Ligularia virgaurea had grown rhizoma. Clonal structures of seedlings have different phenotypes under varying light. Along with increase in shaded grads, plants of L.virgaurea with growing rhizoma significantly decreased. Under conditions of 75% shade, we don't find out the plants that had grown rhizoma. In individual level, there is trade-off between ramets and mother plants. Under the unshaded condition, the length of L.virgaurea's rhizoma is shorter and the branch intensity increases than do seedlings under shaded conditions.