| With growing concern for environmental issues, the ecological function and protection of wetland has been paid attention more and more. On land, wetland is main storage of soil carbon, its soil stocks much carbon. Wetland is generally considered as the "regulator "of greenhouse gas and the "sink" of CO2, it has the vital significance in the global environmental change study. The carbon cycle of wetland ecosystem has become a focus in global change research. And nitrogen is the most important restrictive nutrient of wetland soil and it is the main factor which causes eutrophication of rivers and lakes. Thus, the material cycle of the nitrogen of wetland ecosystems has important practical significance.The water fluctuation zone of Three Gorges Reservoir is wetland which is controlled alternately by land and water formed from the land in the dual interference with nature and human. It is unique wetland ecosystem. The highest water level of Three Gorges Project was 172.8m (in 2008) and 171.43m (in 2009) respectively. In the study, according to altitude section(145-160m,160-170m,170-175m) of water fluctuation zone of the Small River Basin in Three Gorges Reservoir, all soil samples were taken in 2008 and 2009. Through the analysis of experimental data by SPSS 17.0 and EXCEL 2007 after the determination of basic properties of soil samples in laboratory, the main conclusions are as follows.The main types of soil are purple soil, yellow soil and damp soil in the study area. The soil texture of samples was little light and there was much more sand content in the soil. The mean of sand content was 39.11%. the maximum was 82.33%.The distribution of soil pH was mainly at 7.5-8.5. it reflected that the soil was neutral or weak alkaline. There was a lot of K and P in the nutrient elements of the soil, but N was little. The average content of N was 85.90mg·kg-1. CV was 27.74%. The average content of hydrolyzed nitrogen was 63.19mg·kg-1, CV was 39.40%. The average content of total phosphorus and available phosphorus was 1.11g·kg-1 and 16.71mg·kg-1.The average content of total K and available K was 21.26g·kg-1 and 71.24mg·kg-1.SOC was generally at a low level in the study area. Its content ranged 4.83-20.25g·kg-1 and the mean was 11.18g·kg-1. All the factors such as soil parent materials, vegetation, land-use and flooding affect the content of SOC. From statistics analysis about SOC, the content of SOC under different land-use patterns prior to flooding was quite different in the study area. The order of the content of SOC was paddy field(14.75g·kg-1)>grassland(11.94g·kg-1)> abandonment land(9.88g·kg-1)> dry land(9.10g·kg-1). Through the comparison of SOC content in 2009 and 2008, it was found that the SOC content of 2009 was higher than that of 2008 in the study area. Therefore, flooding environment is conducive to the accumulation of soil organic matter.Through the analysis of nitrogen content in the soil of different regions or different land-use patterns in the study area, the result was that the variation of soil nitrogen content and SOC content was consistent. The order of the content of soil total nitrogen and available nitrogen was paddy field> grassland> abandonment land> dry land. The duration of flooding also affected the soil content of nitrogen, but the zone which was flooded longest had not the highest content of nitrogen. Where the soil was flooded as much time as dried there was rather more conducive to the accumulation of nitrogen. If the soil was flooded only extremely short time that can lead to the accumulation of soil nutrients decreased. The soil nitrogen content of 2009 was more than that of 2008 in the study area. It varied with the same trend of SOC.Study on relationship between carbon/nitrogen and soil flooding situation showed that the flooding condition was favorable for the accumulation of carbon and nitrogen in soil. Study showed that there was good correlation between SOC and N. Study on soil C/N value showed that the order of the content of soil C/N value among different land-use patterns was paddy field> abandonment land> dry land> grassland. Because organic matter with high C/N value decomposes slowly, it is favorable for preservation of SOC. Summary, when the nitrogen content is in a certain level, the sequestration capacity of soil carbon in paddy field is stronger than other land-use patterns.Therefore, those may show that paddy soil under long-term flooding is potential "carbon sink". The soil organic nitrogen is main form in the soil N. The more soil organic matter, the more soil nitrogen. To a certain extent, the soil which is in flooded condition plays the role of "nitrogen sink". The content of SOC and N in 2009 was higher than that in 2008 in the study area. It showed that wetland soil of Three Gorges Reservoir played the role of "carbon/nitrogen sink."...
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