关键词: 绿洲, 生态系统, 环境特点, 运行机制

Abstract: Being different from those in other ecosystems on environmental characteristics, structure and work mechanism, oasis ecosystems are the most important ecosystems in arid land. The conception, environmental characteristics, structure and work mechanism of oasis ecosystems are systematically discussed in this paper. The results show that oasis ecosystems are the systems existing only in arid land, they have higher productivity with denser vegetation that lives on the external natural water resources. The main types of the oasis ecosystems in Xinjiang include oasis farmland, oasis human settlements, lower grassland and plain Togay ecosystem. The environmental characteristics have basic influence to the oasis ecosystems. On the climate, there is airflow exchange between the oases and the deserts. It is observed that the coo-l wet air is transported from the oases to the deserts, and the deserts perform an opposite process. The wet airflow from the oases takes a part in the hydrological process in the deserts. On the hydrology, the water resources are relatively richer and more stable on the oases. Most of surface water flow is channeled by human in farmland and cities in the upper-middle area of the oases for the use of human production and life, the lower grassland ecosystems exist only on the underground water which formed by the outlet water from the farmland. An investigation of some typical vegetation shows that the depth of the underground water table and the quantity of the underground water influence critically the state of the lower grassland ecosystems. The soil types in the oases vary in a certain law from the upper to the lower reaches along the surface water flow on the oases. Generally, the soil types from the upper to the lower reaches are：zonality soils (gray desert soil) -hydromorphic soils (bog soil, meadow soil) -solonchak. In the area of farmland, the soil reformed by the people is as oasis soil. The influence of human activities to the natural oases expresses on the two aspects：one hand, the natural oases are the objects of the human cultivating; on the other hand, the priority on water distribution hold by the artificial ecosystems causes great negative influence to the water use of the natural oasis systems. The former makes the area of oases become smaller and smaller, the later makes the living environment of the natural oasis systems become worse and worse. A complete oasis system is organic entirety linked by the water flow from the mountain area, from the upper to the lower reaches, it spatially composed by： (1) the mesophyte on the spring overflow zones, (2) vegetation along the rivers, (3) vegetation on the salic lower land at the lower reaches of the ancient rivers and the flood plain, and (4) lakes at the ends of the rivers. Many of the modern oases have no complete structure because of the interference of human activities. Many lakes at the ends of the rivers were dried up, which leads all the salic materials deposit on the oases. That is an important element causing salinization in the oases.

Key words: oasis, ecosystem, environment, work mechanism