The Reponse Of Plant Communities And Its Ecological Stoichiometry Of Alpine Meadow To Freeze-thaw Degradation In Qinghai-Tibetan Plateau

Alpine meadow is the main vegetation type of grassland ecosystem in the Qinghai-Tibet Plateau, and it has rich native biological resources and precious alpine plant with anti-stresses genes, plays important roles in animal production with plateau characteristics, regulates river catchment capacity and maintains regional ecological security. However, the degeneration of alpine meadow seriously threatens ecological, productive and livelihood security throughout the rivers. The factors contributing to alpine meadow degradation mainly include artificial and natural factors, in which grazing and engineering construction are mainly artificial factors and global warming and rat trouble are mainly natural factors, neglecting freezing-thawing cycle, which is an important factor to cause alpine meadow degradation. On the basis of different degree of freezing-thawing degradation, This study investigated the composition of plant communities, cover, height, diversity and aboveground biomass and determined the content of C, N and P in dominant plants and soil at natural, light, moderate and severe degradation stages of alpine meadow caused freezing-thawing cycle for clarifying the features of alpine meadow and stoichiometry in the process of freezing-thawing cycle, which would benefit to propose the recovery strategies for the alpine meadow degradation from optimizing plant community composition and improving nutrient supply in the permafrost region of the northern Tibetan Plateau. The main results were as following,1. The features of plant communities at natural, light, moderate and severe degradation stages was clarified in this studyThis study showed that the plant community composition of alpine meadow at natural, light, moderate and severe degradation stages was different, indicating that the domination of sedge and gramineous plants gradually decreased, and poisonous and unpalatable plants in leguminosae and compositae gradually increased as the freezing-thawing degradation increased.2. This study explained the response of community and productivity of alpine meadow to freezing-thawing degradationPlant community cover and species richness index firstly increased and then decreased, and community height and aboveground biomass decreased gradually, while (3-diversity index increased in the process of freezing-thawing degradation, indicating that the freezing-thawing degradation increased the habitat heterogeneity in the study region.3. This study disclosed the effect of the freezing-thawing degradation on C, N, P stoichiometry of dominant plants of alpine meadowThe results of this study showed that the freezing-thawing degradation did not affect the C content and decreased the N and P content of Carex moorcroftii, while C:N, N:P and C:P of Carex moorcroftii increased gradually, probably caused by a greater shortage of soil P in the study areas, which suggested that the application of phosphate fertilizer is beneficial to encourage the healthy growth of dominant species.4. This study explained the respose of C, N, P stoichiometry of alpine meadow soil to freezing-thawing degradationThe C, N, P content and N:P and C:P in soil decreased with the increase of freezing-thawing degradation, indicating that the soil nutrient lost gradually in the process of freezing-thawing cycle, which suggested that the supply of soil nutrient is a basic way to restore alpine meadow degradation.5. This study proposed the restorable strategies for alpine meadow degradationThis study proposed that the Medicago ruthenica from legumes and Elymus nutans and Qinghai bluegrass from gramineous were used to sow by mixture though bunch and reseeding pattern. The cattle and sheep manure had to return to natural meadow by finding other energy instead of animal feces. and poultry dung was used to improve the situation P limitation.