The Formation Of Secondary Bare Land In The Source Regions Of The Yellow River And The Ecological Relationship Between Species Of Plant Community

The "black soil land" is a special style in tibetan plateau of the global grassland degradation. It was divided into three stages in this study, which are the embryonic period, the transition period and the forming period. we used space instead of time,combination quantity ecology ,breeding ecology and chemical ecology these methods to research about the composition of grassland vegetation in different stages,the association between the major plant species,the width and overlap degree of the niche of the advantage species and the vegetative propagation characteristics of the main toxic weed. At the same time we aslo made some preliminary exploration about the Pedicularis Gansuensis allelopathy. Preliminary revealed the alpine grassland degradation in the "three-stage" induced a series of community characteristics change according to quantitative ecology, reproductive ecology and chemical ecology. Looking forward to provide some theoretical basis for the latter improvement and restoration of natural grassland.The results showed that:Variance tests and 2×2 contingency table analyses were used in quantitative analysis of the interspecific association among the plant species of the three stages in the source regions of the Yellow River. The results showed that the degradation of Alpine meadow affected the overall interspecific association of plant communities'changes from 58.2141 to 94.8654. And with the increased level of the degraded meadow, the overall interspecific association among main plant species of the community also transformed from significant- negative correlation to none. With the same living form and water ecotypes species from the relationship of interdependeney converted to competition."Black soil land"secondary poisonous weed community tends to be more random and accidental. With the increase of grassland degradation, the competition between some poisonous weeds and edible forage became more intense.Soil in the source regions of the Yellow River tends to be drought and salinization because of the increased degradation of grassland. The dominant species in the community has occured great changes. The community of cyperaceae and gramineae changed to the miscellaneous plant community. The utilization of grassland has been degraded, and even evolved into secondary bare land.The niche breadth of Kobresia humilis,Elymus nutans,Poa crymophila,Kobresia pygmaea and Koeleria var. cristata are more than 0.9, like generalist. Ajania tenuifolia,Lagotis brachystachya,Stipa aliena have narrow niche breadth, like specialist. The larger niche overlap species are Kobresia humilis and Kobresia pygmaea (0.9948),Poa crymophila and Kobresia pygmaea(0.9881),Kobresia humilis and Poa crymophila (0.9811). The smaller niche overlap species Stipa aliena and Ajania tenuifolia (0.2984),Stipa aliena and Lagotis brachystachya (0.3071) Stipa aliena and Ajuga lupulima(0.3909). The dominance of wide nitch cyperaceae and gramineae community are lower but narrower niche of miscellaneous grass are higher than before, because of its unique ability to adapt, with the increased degradation[0] of grassland, and their advantages in the communities also increased.With the increased degradation[0] of grassland, the asexual reproduction [0]characteristics of Ligularia virgaurea has changed, plant height, branching intensity, and the underground biomass and the internode length all increased with the aggravated degradation of grassland. The important values of Ligularia virgaure in the grassland have increased too. This is the typical embodiment of the cloning plants for survival adaptation. Lagotis brachystachya reflects a strong vegetative propagation characteristic[0] in survival competition as a typical cloning alpine meadow. Grassland degradation, the lack of nutrition these have led Lagotis brachystachyas to increase the branching number , so put more capital for the underground biomass , enlarge its scope and access to deep-level nutrition that will ensure the base line growth.[0] This is also the specific risk-sharing features[0] of the cloning plants. Cloning of configuration changes in response, the grassland degradation caused by changes in the level of resources.The aqueous extracts from Pedicularis Gansuensis can restrain the seed germination and seedling growth of Poa.pratensis observably, and its effect with the increase of its concentration increased. However, there was no significant effect both for seed germination stage and seedling growth stage of Elymus nutans. Through field visits, we found that Pedicularis Gansuensis can affect Elymus nutans and the mixture of Poa.pratensis grassland ground biomass. Pedicularis Gansuensis invade and poisoning to artificial grassland on a powerful ability can not be ignored.Through the research of degraded grassland in"three stages"of the"black soil land"we found that the dominent species in the community has undergone great changes with the increased degradation. Population niche breadth and superposition of the changes not only with the degree of degradation of grassland and exacerbated, while niche in turn driven the degradation of the grassland[0] to a certain extent. The degradation of grassland soil is always lags behind the degradation of grassland vegetation, The changes of configuration of cloning plants, indicates that"black soil land"grassland soil nutrient deficiencies to some exeant. Relevance of the species through analysis that the"black soil land"secondary poisoning pose a weed community tends to randomness and chance,"black soil land"is probably not the ultimate stage of succession. Thought the Pedicularis Gansuensis allelopathy we found that, Pedicularis Gansuensis's unique invasion must draw enough attention at the artificial grassland during the latter part of management.