| Water is the decisive factor to keep the wetland ecosystem stable and healthy, and water level gradient is an important environmental gradient in wetland ecosystem. The fluctuation of water level is not only the key factor which controlled the wetland characteristics but also one of the typical disturbance characteristics of the wetland. Wetland soil is an important part of wetland ecosystem, it is the first place for wetland to obtain chemical substances, and wetland soil is also the intermediary of chemical changes and the direct supporter of wetland plants. The water condition and the fluctuation of water level and soil type, structure and fertility in wetland will affect wetland plant's community distribution and production, community stability, species diversity and community succession. Therefore, it has a great practical significance to research the wetland constructive species in response to fluctuation of water level and soil environmental factors.Shanghai Chongming Island is the most important strategic reserve of land area, the 43.7% of whose area is formed by beach reclamation. During the process of beach reclamation, artificial reclaimed water desalination changes the inorganic wetland environment, and the corresponding plant community composition also changes. The study site is located in the wetland restoration demonstration area of reclaimed land area and the water level of major rivers is controlled. Growth of Phragmites australis in different channels is recorded by sampling method and the reason of differences in Phragmites australis growth and reproduction is explained from water level fluctuations and soil aspects. Based on the research above, we can quantify the relationships between water level, soil environmental factors and growth, reproduction of Phragmites australis, and further to provide basic data for the sustainable use of conservation and restoration of Phragmites australis community, and also to provide a scientific basis for restoration and reconstruction of reclaimed wetland. The main findings and conclusions are as follows:1. The plots in study area has differences in water level, and the water level of the region in spring is mainly surface flooding, summer and autumn is mainly underground water level, the water level in three plots is the lowest in autumn:the average water level of plot 1 is -46.81±23.40 cm, plot 2 is -23.62±15.81cm, plot 3 is-15.50±8.94cm.2. Soil bulk density and organic matter of the plots change with the season as "V" trend, and lowest in summer, soil total nitrogen content decreased with seasonal variation; soil bulk density of plots is above the normal range of 1.1～1.4g/cm3; soil organic matter and total nitrogen are on the low side. Soil bulk density and organic matter are not different between the various seasons in each plot, but soil total nitrogen has differences among the plots only in the fall. In each season, soil water content of three plots increase along with the vertical depths, and the soil water contents of each layer (0-20cm,20-40cm,40-60cm) are closely related with water level. In spring, soil water content of surface layer (0-20cm) is the maximum of three seasons:plot 1 is 306.1±16.4g/kg, plot 2 is 362.4±9.7g/kg, plot 3 is 408.4±20.7g/kg; in summer, soil water content of surface layer (0-20cm) are different between the three plots; in autumn, soil water content of the layer below 20cm varies between the three plots.3. The growth dynamics of the Phragmites australis population density, plant height, basal diameter, leaf number and leaf area per plant, aboveground biomass in the three plots are recorded:the density maximum appears in the summer in plot 2, 152±13N/m2; base diameter maximum is in the spring of plot 1:7.35±0.31mm, the maximum leaf area per plant is in summer in plot 3:547.69±16.67cm2, the maximums of stem length, leaf number per plant and aboveground biomass are in plot 3 in the fall. While the aboveground biomass of Phragmites australis in this region major decision by plant height and basal diameter, and plant height on the contribution of biomass larger than base diameter. The reproduction conditions indexes of Phragmites australis (flowering rate,the number of flowers and seeds) in plot 3 are at the highest values, and each index is different between plots in autumn. 4. From the analysis of the relationship between water level,soil environmental factors and growth and reproduction of Phragmites australis, we can get:when the water level is above the surface, the reed's growth status is directly related to the water level; when the water level is below the surface, the Phragmites australis growth status and reproduction condition are related with the different levels of soil water content, meanwhile soil bulk density and total nitrogen content also determine the reed plant height, the number of flowers and seeds. Above all, the environment of low soil water content, low soil total nitrogen content and high soil bulk density is not conducive to the growth and reproduction of Phragmites australis.
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