| Grassland is a type of land, which has a variety of complex functions, and accounts for 33.6% of the total area in China. The recovery and stability of grassland ecological system is important to maintain the natural ecosystem restoration and stability. Besides, it lays a foundation for the development of animal husbandry. Gannan Tibetan autonomous region in Gansu province is located in the northeast edge of the Tibetan Plateau. It has the typical alpine meadows and grassland. With the development of animal husbandry, of the interference of human factors on the grassland ecosystem is more and more serious, such as overload, overstocking and digging cordyceps with disorderly, which lead to large area of grasslang degradation. Plant community structure has great changes, the proportion of excellent forage decreases, and the covering area of toxic weed increases gradually and forms advantage population. Ligularia virgaurea is a kind of perennial herbaceous plants which belongs to Ligularia of Compositae. It has two breeding ways, sexual reproduction and asexual reproduction. The leaves, roots and stems of the plants have toxicity, especially for cattle and sheep. It is a symbol toxic weed in degenerate grassland of Tibetan Plateau. There must be competitive relationship between Ligularia virgaurea and other plants for the limited resources. Microbial population in prairie soil will change and affect the structure stability of plant community. Arbuscular mycorrhizal (AM) fungi are widely distributing on land ecological system. They can infect the majority of plant roots and form symbiotic association with the plants. So there are many intensive mycelia network in soil ecosystem, through which AM can accommodate the competition balance between plants. So the experiments are carried out field investigation experiment and indoor experiment to explore the relationship between AM fungi and the plant, and reproductive characteristics of the plant.1) The results showed that in 2010, AM fungi infection rate and spores density is at most when the density is medium. In July, the density is higher, Ligularia virgaurea biomass are larger. But in September, Ligularia virgaurea have the largest biomass under medium density, and AM fungi promoted the growth of the plants siginificantly (P<0.05). In 2011, AM fungi infection rate and spores density is also at most under medium density. In July, there is no significant difference among the biomass under three densities (P>0.05). The plants grew older, the biomass with medium density was larger, and the least with high density. There are significant difference between the different treatments (P<0.05). The influences of AM fungi to the plant are affected by time and density.2) Time, density and the interactions have significant difference on the density, height and advantages of adjacent plants (P<0.01). In 2010, with density increasing the height, density of Ligularia virgaurea are increasing, the density is lower; the advantages of neighboring species are more. In June of 2011, there are no significant difference among the height and advantages of neighboring species of three densities (P>0.05). Along with the growth of the plants, its density is higher, the height is lower, and the other advantages of plants are less.3) Under constant temperature, the seeds germination rate of Ligularia virgaurea is the highest with 77.2% at 25 ℃, and seedling survive is the most. The length of buds and roots are the longest at 20 ℃. During variable temperature, the germination rate is the highest with 79.2%, seedling survive is the most at 5-15 ℃, but low temperature limit the growth of plants. The time of vernalization is longer, the germination rate is higher, which can reach to 81.8%, but the buds and roots are shorter. The seed germination rate of medium seeds is the highest with 84.8%, survive of seedlings are the most, buds and root length are the longest. |
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