The Study About Change Of Vegetation And C:N:P Stoichiometry Of Soil In Different Succession Stage In Alpine Grassland

In the Yellow River source region of Qinghai-Tibet Plateau, we selected four alpine grassland stages of degradation succession: gramineae grass-Kobresia humilis community, Kobresia humilis community, Kobresia pygmaea community and the forbs-black soil beach community, and three different enclosed levels of recovery succession, as the research object. Used ecological method to measure vegetation species, biomass, coverage, important value and variety of eco-index in the various successional stages of community, while research content and ecological stoichiometry of the soil organic carbon, total nitrogen and total phosphorus.The following results were obtained:(1) Vegetation changes of communities in the three stages and four periods of alpine grassland degradation succession were:firstly, gramineae and Kobresia were the predominant species of community, had high ecological advantages. With the degradation succession of alpine grassland, aboveground biomass and coverage were decreased, important value of gramineae and Kobresia were gradually decreased, forbs began to invade the communities, important value of the forbs were increased, the number of species were increased, diversity index were increased, when the communities changed into forbs-black soil beach communities, forbs become the predominant species, native vegetation almost disappeared, biological diversity and evenness were decreased, communities structure become unitary. Function of ecology, production and life of alpine grassland were reduced.(2) The loss of soil nutrients, organic matter and total nitrogen content were decreased with succession and soil depth; Total phosphorus were decreased in the early stage of succession, and later did not change significantly; Soil organic matter, total N and C:N value showed a good correlation with the aboveground biomass scale.(3) The soil nutrients had a higher C:N ratio and low N:P ratio in degradation succession process of the alpine grassland, and had different the CNP ecological stoichiometry in different successional stages. It showed that the alpine degradation grassland performanced the limit of N in the succession process. Make sure the soil nutrient threshold of alpine degradation grassland were:C:N>10and N:P>8.(4) Grassland enclosure of alpine degradation grassland could significantly improve the aboveground biomass and coverage, could well improve the situation of grassland soil nutrients, improved soil organic matter, total nitrogen, total phosphorus, and played an important role in recovery and maintain of alpine grassland in Qinghai-Tibet Pleteau.