| L. virgaurea and L. sagitta, which are the most deleterious weeds in psychrograssland, as well as L. przewalskii of genus Ligularia (Compositae) are widely distributed in the east of Qinghai-Tibet Plateau, In this thesis, clonal growth characteristics, plasticity of resources availability and biomass allocation of the three species were researched by employing the method of comparative study between their natural populations and transplanted populations. The aim of this study was to probe into the ecological strategies of the weeds and provide scientific evidences for the management of the toxic weeds. The main conclusion is as follows:1. L. virgaurea and L. sagitta were guerrilla clonal plant of perennial herb.2. In the process of clonal growth, each rhizome only developed a ramet and there was no net or linear clonal growth form. So the clonal architecture of the two species was defined as guerilla pseudoaxis style.3. Clonal hierarchical selection models of L. virgaurea and L. sagitta included four hierarchies: clonal fragment, root of ramet, ramet and genet.4. The type of physiological integration of L. virgaurea and L. sagitta both belonged to splitor. This character might improve invasion ability of ramet in vacant habitat, and adapted to the character of life history that L. virgaurea and L. sagitta presented under transplantation condition.5. Branching intensity and rhizome length of L.virgaurea and L.sagitta increased with the increasing of resource level. When the resource was rich in habitation, the ability of clonal propagation was significantly increased. And ratio of development root reached to 100%. Thus, certain ramets were reproduced.6. Branching angles of L.virgaurea and L.sagitta usually took on radial pattern of 0?and 180?, accordingly avoided the competition among ramets effectively. Their rhizomes developed root system at first. It was easier for roots to live through the winter in the alpine region with short growth season and was propitious to individual plant to survive. This is one of their adapting strategies.7. Under natural and transplantation conditions, L.virgaurea and L.sagitta showeddiversified life history forms. Under natural conditions, they presented S form, while under transplantation condition, V form.8. Root system played a key role for survive, reproduce and live through extreme cold winter in psychro-environment. Under natural condition, root system biomass of seedling was a majority of total biomass and there was a trade-off between root and above organ (leave); in mid-stage of growth, the larger root system was associated to higher biomass of sexual reproduction. During whole growing period, resources allocation to underground biomass presents high-middle-low model. In transplanted populations, L. vigauria and L. sagitta increased obviously their clonal propagation ability and there was a positive relativity between root system and clonal propagation biomass. L. przewalskii presents to be slightly positive between root biomass and clonal reproductive biomass. These results showed root system played an important role in survive and reproduction of the three species.9. Instead of being in accordance with the variety of altitude, the increasing or reducing of the total output of biomass was accordant with resource conditions of populations. When their communities were densely and resources limited, the total biomass were reduced. On the contrary, the total biomass was relatively high.10. Trade-off between clonal and sexual reproduction was not detected during the experimental research.11. L.virgaurea and L.sagitta had two reproductive ways, sexual reproduction and clonal propagation. On grassland where vegetation coverage was higher, the reproduction of the two plants mainly depended on seeds, as the clonal propagation ability was restrained due to the furious competition of underground resources. Once vegetation degenerates and competition between species weaken, the two species will inhabit fleely in local...
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