| Environment in Tibetan alpine grassland is poor, it's characteristics display mainly: alpine, drought, rarefied air, daily temperature difference is large, longer sunshine time,strong ultraviolet radiation,shorter soil formation age,thin soil layer,low degree soil weathering,high gravel content and low vegetation richness. Research on nitrogen storage rules of differentiation of alpine grassland falls into vertical gradient and horizontal distribution of vegetation biomass and soil nitrogen distribution nitrogen storage,the paper analyzed and discussed main factors lead to such differences and changes.First,Alpine grassland ecosystems vertical differentiation gradient nitrogen storage laws1 Alpine grassland ecosystems is affected by topography, climate, soil and the impact of a high degree of posters,the genera aboveground biomass nitrogen (Kg N ? m-2) is low,With the elevation,aboveground biomass was slowly increasing in nitrogen. Different altitude, alpine grassland distribution of vegetation types are significantly different.2 Alpine grassland ecosystems on the elevation gradient on soil properties affect the total biomass of nitrogen significantly,nitrogen level of total biomass was significantly lower than the national average,soil temperature, moisture content and soil bulk density affected biomass nitrogen significantly, when the soil bulk density is between 1.4 g ? cm-3 and1.5 g ? cm-3 , the total biomass nitrogen reaches its maximum.3 Below-ground biomass nitrogen is main vegetation nitrogen storage pool in northern Tibet alpine grassland ecosystems. 40cm deep underground biomass plot total biomass of more than 90% of the elevation gradient of nitrogen below-ground biomass significant difference test showed that below-ground biomass of 4460m above sea level was significantly higher than other elevation gradient, below-ground biomass nitrogen and soil temperature have a positive correlation, between soil temperature below-ground biomass into an upward trend in nitrogen, as the soil temperature up, below-ground biomass nitrogen turned up an upward trend.4 Northern Tibet alpine grassland soil nitrogen overall density levels were significantly lower, it is low nitrogen density areas in China, vertical density nitrogen gradient change greatly. Nitrogen density trends are: 4830m(0.9892 gN·m-2)>4900m(0.9684 gN·m-2)>4663m(0.9012 gN·m-2)>4610m(0.8644 gN·m-2)>4421m(0.7748 gN·m-2)>4518m(0.6132 gN·m-2)>4562m(0.6112 gN·m-2)>4775m(0.5844 gN·m-2)>4470m(0.4132 gN·m-2)>4720m(0.1432 gN·m-2).Second,The level of alpine grassland ecosystems at different scales of nitrogen storage laws1 The highest aboveground biomass nitrogen values of the level of scale appear in the Cuoqin county for 0.767 g N ? m-2,lowest in the Zhada county as 0.102 g N ? m-2,northern Tibet alpine grassland gradient aboveground biomass on the level is0.3492gN ? m-2 on average. Aboveground biomass center were Cuoqin County, Anduo County and Ritu County, forming three gradually reduced toward four sides and showing the distribution of radial distribution pattern of aboveground biomass.2 there is a clear regional differences in 40cm deep northern Tibet alpine grassland biomass nitrogen, The high nitrogen below-ground biomass are Ritu County, Naqu County, Anduo County, Zhada County and southern Zhongba County, reacheing 4.56gN ? m-2-12 gN ? m-2,the highest up to 12gN ? m-2, forming higher nitrogen below-ground biomass in northern Tibet Area, higher nitrogen below-ground biomass for the northern region east line of alpine grassland. Various points of other below-ground biomass ranged from 1.221 g N ? m-2 to 2.756 g N ? m-2 , formeing Geji County, Gaize County, Nima County, Shenzha County and Cuoqin County the center of the lower region below-ground biomass nitrogen.3 Soil nitrogen density and environmental factors analysis showed that 40cm soil nitrogen density and temperature are closely related, temperature is of the main factors of 40cm deep soil nitrogen reserves, soil nitrogen density and soil bulk coefficient is -0.02, reaching the level of significant negative correlation, it showed the impact of soil bulk density distribution of soil nitrogen. When the soil bulk density is between1.4 and 1.5g ? cm-3, the highest density of soil nitrogen is achieve. Density of soil nitrogen and soil particle composition analysis showed that the density of the formation of soil nitrogen and soil particle size is directly related to each other, the higher content of soil particles between 0.25 and 0.075mm, the smaller corresponding density of soil nitrogen. The higher content of soil particle≤0.075mm, the smaller density of soil nitrogen. |
PDF Full Text Request