Breeding System And Ecological Adaption Of Three Species Of Genus Ligularia In The East Of Qinghai-Tibet Plateau

Ligularia sagitta, L. virgaurea, and L. przewalskii of genus Ligularia (Compositae) are distributed in the east of Qinghai-Tibet Plateau of China. Among them, the former two plants with the behavior of sexual reproduction and clonal propagation are dominant poisonous weeds on the alpine grassland, and their damages to grassland are serious with each passing day. In this thesis, the breeding system and reproductive strategies of the three species were observed and analysed. The adaptation and evolution of the genus Ligularia under the condition of psychro-environment were discussed.The result showed that the flowering and fruiting periods of the three species were from mid-June to the beginning of October, and their inflorescences were racemose arrangement with capitulum. The outcrossing index were 4 in the all three species, the breeding system was given priority to outcrossing, part self-compatibility, insects pollinator-dependent. The main factors effecting the success of sexual reproduction were pollinators scarcity and insects infection.The primary factor to limit seed setting was the windy psychro-environment which limits the activities of insects, leading to the insect number to visited flowers decreased. All these factors induced the low setting percentage. But the plants didn't accept this fact passively, instead they took active strategies of adaptability, such as mass blossom, prolonging the functional period of female and male gametophyte, and generalization of pollen medium. Therefore, the potential of sexual reproduction in the three species was still very great.Under natural conditions, the clonal growing rhizomes of L. sagitta and L. virgaurea were suppressed due to interspecific competitions on the grassland, therefore the reproduction of the two plants mainly dependen on seeds. This fact suggests, we should aim at sexual reproductive organs in management of the two weeds, we also need to pay more attention to ecological recovery on the degenerating grassland to prevent land form further desertification.