Physical And Chemical Properties Of Soil Of Vulnerable Ecosystem In Lhasa,Tibet

Soil is the foundation of terrestrial ecosystem, and it is an important component of the land surface environment. The physical and chemical properties of soil not only affect the exchange of energy and material between organisms and environment, but also affect the composition of plant community, and restrict the stability of the ecosystem. In recent years, due to global warming and human activities, the degradation of alpine ecosystem in Tibet is more and more serious, and the ecosystem becomes more vulnerable. The research on the properties of soil in fragile ecological zones contributes to monitoring the state of the ecosystem and promoting the functions of ecosystem services.In this study, we chose two types of fragile ecosystems in Lhasa Valley, including shrub meadows and wetlands. And four depth levels(i.e., 0-5cm, 5-10 cm, 10-20 cm, 20-30 cm and 100cm) of soil samples were collected from the 4000-4800 m altitude range of shrub and meadow areas. Then, we analyzed the temperature, nitrogen, phosphorus, potassium, organic matter, pH and calcium, magnesium, sodium, iron, manganese and other elements of the content. At last, the method of data statistics was used to analyze the spatial heterogeneity of soil physical and chemical properties of fragile ecosystem, and correlation analysis were done between different indicators. The main conclusions are as follows:(1) The change characteristics of soil temperature surrounding the shrub meadow and wetland of Lhasa. The change of soil average daily temperature in the year showed a cosine curve and the diurnal variation of soil temperature showed a sine curve. Soil temperature of shrub meadow was lower than that of wetland. The diurnal variation of soil temperature in the wetland during the year(12.13℃) was slightly higher than that of the shrub meadow area(11.63℃). Soil freezing time(147d) was significantly shorter than that of the shrub meadow in a year in the wetland(53d). But the heating rate and cooling rate of wetland soil were higher than that of shrub meadow. The soil temperature of shrub meadow and wetland soil in 20 cm depth is stable.(2) The soil physical and chemical characteristics of shrub meadow and wetland areas. In the shrub meadow area, the soil was acidic, and the soil was neutral in the wetland. Except for calcium and manganese, the content of soil nutrient in shrub meadow was higher than that of wetland. The content of organic matter, total nitrogen and calcium decreased with the increase of soil depth, and the total potassium, sodium and iron increased with the increase of soil depth. There was no significant correlation relationship among total phosphorus, magnesium, manganese content and soil depth. While the organic matter, total nitrogen and manganese content in the wetland soil decreased with the increase of soil depth, and the increase of calcium, iron and p H showed an upward trend with the increase of the depth. The correlation relationship among total phosphorus, total potassium, sodium, magnesium content and soil depth is not obvious.(3) Correlation relationships among soil nitrogen, phosphorus, potassium and organic matter, temperature and other indicators in shrub meadow and wetland soil. Correlation relationships among soil organic matter, nitrogen and phosphorus in shrub meadow and wetland were high. However, the nitrogen, phosphorus and potassium in the soil of shrub meadow area show obvious vertical distribution, and the soil temperature is an important influence factor. The altitude of wetland soil ranged in a small region, and the correlation relationship between the distribution of N, P, K of the soil is poor. The correlation relationship between total nitrogen and soil pH value in wetland soil was obvious, but the relationship between soil nitrogen and pH value in shrub meadow was not obvious.