Reproductive Strategies Of Typical Clonal Plant Ligularia Virgaurea At Alpine Meadow In Qinghai-tibetan Plateau

Ligularia virgaurea is one of major weeds in the alpine meadows on the eastern Qinghai-Tibetan plateau. L. virgaurea has become the advantage toxic weed in deteriorated grassland, because of continual over-grazing and selective predation by livestock. In this study, we conducted4years field control experiments and3years field investigation to discuss the effects of the biotic and abiotic factors on clonal growth and sexual reproduction, and the relationship between two reproductive modes at the genet level. In order to fully understand the influence of this species on grassland environments, we also investigated the effect of L. virgaurea on soil properties. Through field observation, we investigated the relationship between floral display and pollinators or predators, as well as the effect of floral display on female reproductive success, and discuss the possible defense mechanisms of L. virgaurea. Because of gynomonoecy system has been paid little attention to the adaptive significance, so in this study, we used3kinds Ligularia species:Ligularia virgaurea, Ligularia sagitta, Ligularia przewalskii as materials, and investigated the effects of external and internal factors on the flower traits within inflorescence, and discuss the evolutionary significance of gynomonoecy system. The main conclusions are as follows:1. Density, light and nutrient has selection pressure to genets’growth traits in different degree.2. Clonal growth is density and light dependences, lower density and higher light intensity promote the clonal growth.3. Sexual reproduction is not density and light dependences, but higher nutrient level promote the occurrence of sexual reproduction by increase the genet size.4. Both sexual reproduction and clonal growth show a positive linear relationship with genet size. A threshold size is required for sexual reproduction and no evidence of a threshold size for clonal growth. Light determined the onset of sexual reproduction, and the genets in the shade required a smaller threshold size for sexual reproduction to occur than the plants in full sunlight.5. No evidence was found of trade-offs between clonal growth and sexual reproduction under different densities and light conditions at the genet level.6. In natural communities, the species diversity, sedges and weed coverage decline with the increasing density of L. virgaurea, but this species had no effect on soil properties. The mainly harm of this species on grassland environment is the rapid space expansion by cloanl growth.7. The pre-dispersal seed predations of L. virgaurea are more than one insect, including Syrphidae, Anthomyiidae and Noctuidae insects, and they are also the important pollinators. Floral display size is the compromise of the evolution between pollinator selection and seed predators.8. L. virgaurea can not reduce predator damage by flowering synchronization or change the floral display size and the flowering phenology. Producing more bisexual flowers ovule in the later flower heads is an effective means to reduce the damage of the predators.9. Three Ligularia were self-incompatibility, and the intra-inflorescence variations in floral traits were significantly:the early flower heads have larger flower display and female-biased sex allocation; the later flower heads have more ovule and male-biased sex allocation. Plant height and leaves removal were not change the variation of floral traits within inflorescence.10. The adaptive significance of Ligularia lies in permitting flexibility in allocation of resources to male and female functions and in attracting pollinators, but in reducing conflict between male and female function and in insect predation can not be ruled out.