Effects Of Fertilization On Vegetation And Soil Of Degraded Grassland On Northern Tibetan Plateau

In order to explore the scientific approaches to restoring degraded grassland in Naqu Prefecture of Tibet, plot fertilization experiments are carried out, and effects of different fertilization applications on vegetation and soil of degraded grassland are systematically compared in such respects as height, coverage, richness, aboveground biomass, niche, and physical and chemical properties of soil, based on which effects different fertilization applications on improving degraded grassland are evaluated. The main results are as follows:(1) On the whole, compared to the control, the application of organic fertilizer with phosphate fertilizer can significantly increase total aboveground biomass while dramatically reduce weed production and its relative biomass. It can also increase the yield of legumes, sedges and their relative biomasses. Therefore, from the socio-economic perspective, organic fertilizer with phosphate fertilizer proves to be a better application to increase total aboveground biomass and proportion of fine forage grass on degraded grassland. However, in consideration of protecting biodiversity and promoting sustainable development, organic fertilizer is better. It is difficult to achieve both goals at the same time.(2) Overall, compared to the control, the application of nitrogen fertilizer with phosphate fertilizer can not only raise average height of degraded grassland vegetation, but also improve relative coverage of grasses noticeably while reduce that of weeds. Hence, in terms of landscape benefit of ecological system, nitrogen fertilizer with phosphate fertilizer is optimal application.(3) Relationship between diversity index and aboveground biomass is that in areas with application of organic and phosphate fertilizers, diversity index is in a clear positive linear correlation with aboveground biomass; and it displays a clear negative linear correlation in areas with no fertilizer, with phosphate fertilizer or with nitrogen and phosphate fertilizers. (4) Niche breadths of major species widen markedly after fertilization. Meanwhile, fertilization plays different roles in different species. Adaptability of Roegneria nutans, Saussurea spp.and Potentilla bifurca improves, while that of Stipa purpurea, Kobresia littledalei and Subsessiliflora decreases. Niche overlap is greater between weeds and sedges, weeds and grasses, among weeds and among grasses. Species competitions exist chiefly among them.(5) In various fertilization applications, soil moisture in various sample land progressively diminishes with increase of depth, whereas bulk density of soil gradually increases. Chemical fertilizers combined with organic ones can increase soil nutrient content most in degraded alpine grassland, followed by applications of organic fertilizers only and chemical fertilizers only.