Effects Of Enclosure And Grazing On The Vegetation Restoration And Soil Fertility Improvement Of The Desertification Grassland In Northwest Of Liaoning

The Namusilai Nature Reserve, which was founded in 1987, is located in the dry sandy area within north-west of Liaoning province. Now it has been enclosed more than 20 years, and has been for a natural sandy grassland vegetation sample. It has a profound significance to get the vegetation structure and character of soil nutrient recovery, because it has a very good reference to construct vegetation restoration of wide range degradation sandy grassland. Therefore, combining with needs of restoring degraded grassland in Liaoning Province, by taking Namusilai Nature Reserve as the research object, the present paper has researched the community structure and stability character. Applyed Levins Index and Pianka Index, the niche breadth and niche overlap of main plant populations in the fenced grassland were measured. Besides, the present paper has been analyzed characters of N, P, K contents and storage in different soil layers and their response of different land-use types. Finally, it has selected the methods of organic carbon density and analyzed the change rules of organic carbon storage and dynamic change characteristics of soil carbon sink and source under various land-usages. Main results are as follows:1. It appeared 58 higher plant species belonging to 22 families and 50 genera in 60 plots. Gramineae, Compositae, Leguminosae, and Rosaceae occupied high proportion, about 57%. From the stucture of life stytle, trees, shrubs and perennials consisted of 79 %. The ecotype components consisted of 61% of mesophyte,36% of xerophyte. Population frequency data showed that Lespedeza daurica, Cleistogenes squarrosa, Agropyron cristatum, Artemisia halodendron, Artemisia frigida had taken up much of plant resources, they played an important role in the process of building group. After more than 20 years of seal protection, sandy shrub communities including artemisia shrubs and grasses had been mainly plant community.2. The niche breadth of Lespedeza davurica, Cleistogenes squarrosa, Artemisia halodendron, Agropyron cristatum, Artemisia frigida, Miscanthus sacchariflorus, Thalictrum squarrossum, were 0.95,0.8,0.75,0.75,0.65,0.63 and 0.6 respectively, which were greatly higher than other species, and they had formed common dominant species. There were 27 plant populations, which niche breadth was smaller than 0.1, making up 46.6% of the total. The niche overlap of most species was between 0.3 and 0.6, accounting for 71% of all species-pairs. The niche overlap index among the 7 populations that had the widest niche breadth was between 0.57and 0.88. It had formed the pattern that a few species with larger niche breadth had higher niche overlap.3. Community stability test results showed that the cross points between the ratio curves of species percentage and accumulation relative frequency and an endpoint line of coordinate axis was 29/71. It had a certain gap to 20/80, so the community remained in a precarious successional stage.4. The data of edaphic nutrient showed that with deepening of soil layer, edaphic total nitrogen content of enclosed grassland was reduced significantly. But there was no such feature in the grazing land. The change of edaphic total phosphorus and potassium content were complicated in the enclosed grassland and grazing land, and not had any regularity. The dynamic change of edaphic nutrient storage was obvious in the enclosed grassland. But it was not obvious in the grazing land. After more than 20 years enclosed, the soil nutrient of enclosed grassland had a good recovery.5. With deepening of soil layer, the content of soil organic carbon in enclosed grassland was reduced significantly. But there was no such feature in the grazing land. Soil organic carbon density of the fenced grassland in 0～30 cm soil layer varied from 2.8 kg·m-2 to 4.0 kg·m-2 and the range was 1.2 kg·m-2. Soil organic carbon density of the grazing land in 0～30 cm soil layer varied from 3.4 kg·m-2 to 4.7 kg·m-2 and the range was 1.3 kg·m-2. General speaking, to the fenced land, from May to August and from September to November both were carbon source process, from August to September was carbon sink process. However, soil carbon storage of the grazing land was more stable, conversion of soil carbon sink and source was no significant.