| In arid and semi-arid areas, the land salinisation has become very serious because the earth's surface evaporates strongly and highly-mineralized ground water rises above the critical depth. Therefore, the spatial and temporal dynamic of the soil water and salinity, the ground water table and salt concentration are main factors affecting the oasis stability. The plant develops various physiological mechanisms to adapt for the water and salt environment in the long run. Because of rare rainfall, the plant absorbs water from deep soil and ground water with bulky root system for maintaining the physiological function. Consequently, the dynamic of ground water table and water quality has an intense influence on the growth of vegetation. The soil water and salt system is complicated, consisting of ground water and water content, salinity, nutrients contained in soil. Although it is not a problem when salt remains deep in the soil (indeed this is the definition of primary salinity), it is a major problem when the salt is brought close to the surface, upsetting the naturalwater balance.The dynamic of ground water, affected by climate, hydrological cycle,vegetation and various artificial factors, is the significant reason for the dynamic of land salinisation and land cover/land use. The spatial and temporal distribution of water resource is the dominant factor that influences the dynamic of ground water. The influence displays mainly in the seasonal and spatial dynamic of ground water table and water quality. For this reason, to analyze the spatial and temporal dynamic of ground water table and water quality beneath the typical phytocommunity in particular areas, will be helpful to probe into the dynamic formation of soil moisture and salinity, and to understand the spatial variation of vegetation. The dynamic of ground water is also influenced by local climate, such as temperature, humidity, wind speed, and so on. Because of the evaporation, dissolved salt is brought to cumulate at the ground surface and the root zone when the ground water is above the critical level. Then the saline soil is formed.The ecotone is situated in the oasis periphery and affected by artificial factors profoundly. Over grazing and exploitation have caused the steady ecotone system to deteriorate. The influenced scale reaches to 40~60km, and the vicinity of oasis area within 3~6km is affected the most. The vegetation coverage is sharply declined to 2%~3% and even worse. Take oases to the north of Tianshan Mountain in Xinjiang as an example, the vegetation coverage of the areas is even lower than that of the desert outside. As a result, these regions have become the zone of facture, which threatens the existence of oases instead of maintaining their stability.This paper focuses on a comparison between areas beneath desert phytocommunity and oasis areas in terms of the dynamic of soil moisture and salinity together with its impact on phytocommunity. To illustrate this point,VIthe dynamic of the water and salt in Fukang oasis will be analyzed. By comparative analysis of the dynamic of soil moisture and salinity in farmland, the abandoned land inside new oases, sand dune and the grassland periphery, the influence of dynamic state of soil moisture and salinity on the oasis stability can be clarified. Thus, we may draw the following conclusion:l.At the plains in Fukang, the ground water table rises gradually from south to north, and it falls in the desert. During the growing season, the ground water tables at each sampling point are falling, but the total salinity of the soil does not change much.2.The change of water content and salt concentration in soil is a dynamic process of balanced accumulation and consumption. It is influenced markedly by the ground water table.(l)The dynamic of the water and salt at the oasis peripheryIn the horizontal direction, the water content and salinity of soil increase gradually from south to north, and fall in the desert. In the vertical direction, water content and soluble sa...
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