| Ecosystem will produce nitrous oxide (N2O) gas into the atmosphere, which is a major part during the nitrogen cycle. The impact on the global climate cannot be ignored. N2O accounted for 70% to 90% by nitrification and denitrification from ecosystem, of which a large part of N2O was produced by soil microbes. According to the report of the United Nations Intergovernmental Panel on Climate Change (IPCC) in the fourth assessment, N2O content has increased from 270×10-9 during the period of pre-industrial to 319× 10-9 in 2005. Carbon dioxide is the most important greenhouse gas. Compared tocarbon dioxide, N2Oconcentration is at a very low level in the atmosphere. However, the monomolecular warming potential of N2O is 310 times than that of carbon dioxide.A number of studies indicated that there was a strong association between N2O flux with soil properties, moisture content, electric conductivity and other environmental factors. In addition, it could be affected by microbial populations and other biological factorsclosely. Coastal wetland is a major coastal ecosystems and an important source of N2O. As the second largest wetland in the world, it is famous for its large size and good state of vegetation. Guan Daoming has discovered that Liaohe was an important source of N2O. But researches on vegetation restoration of wetland and N2O flux is rarely studied, no matter about the relationship and mechanism.With the development of Liaohe Phragmites wetland, a series of ecological problem has showed up, including the declining and degradatioinof natural wetland. Ecological problems have been more and more serious. In this study, sampling sites were selected from degraded wetland, restored wetland and natural wetland during the process of vegetation ecological recovery.The influencing factors about N2O flux from wetland sediment water-air interface were studied.This study investigated N2O flux and its influencing factors in typical degraded wetland, restored wetland and natural wetland of Liaohe estuary in July and September,2014. The results showed that Liaohe estuary wetland was a source of N2O, the N2O emission flux decreased in turn from degraded wetland to restored wetland, and to natural wetland. Furthermore, N2O emission flux in fall was significantly higher than in summer. The daily variation of the N2O emission flux was significantly affected by environmental temperature. The absorption could be affected by temperature variation in the morning and evening. In addition, N2O flux showed a significant positive correlation with air temperature, box-temperature, ground temperature and electric conductivity, while a negative correlation with the moisture content. N2O flux of three types of wetland was primarily affected by ammonia nitrogen, nitrate nitrogen, TOC, the ratio of C:N in wetland sediment. There was a strong relationship between vegetation restoration of wetland and and N2O flux by affecting temperature, moisture, electric conductivity and sediment nutrient substance.Hence, vegetation restoration improved the soil nutrient content effectively and simultaneously inhibited the N2O release of wetland sediment. Although the global warming potential of restored wetland was higher than degraded wetland, it has been 15%lower than natural wetland. The values of the global warming potential (GWP) in per unit yield of degraded wetland, restored wetland and natural wetland are 4.323, 3.689,3.043 g/m2 in future 100 years. Therefore, ecological restoration of Phragmites australis in degraded wetland was one of the key measures in reducing N2O emission.We made an cultivation with a tempreture of 25 ℃, and a water holding rate of 80% in the three types of atmosphere environment with air, oxygen and argon. The cultivation last as long as 192h. The content of N2O was measured 24 hours to make sure the N2O producing rate. Denitrification was the main procedure to produce N2O. The contribution of N2O with denitrification accounted for 74%,68%, 109%.Followed by denitrification was the heterotrophic nitrification, the amount of N2O contribution were 32%,64%,105%. Autotrophic nitrification contribution of N2O emissions were-24%-45%-98%. And nitrifier denitrification contributed 19%, 13%,-16%, respectively.The molecular biology method of PCR-DGGE was used to study the change of nosZ genewith time and space variation. The results showed that the population of bacteria with nosZ at different times in the same area had a big difference, but there was a high similarity for some bacteria with nosZ genes at the same time in different areas. Ecological restoration improved the structure and the populationof degraded wetland soil effectively. A positive inhibition was proved for the release of N2O.Vegetation restoration improved the content of soil organic carbon and dissolved oxygen effectively. Also, it has played a significant role in inhibiting N2O emission.The soil properties of restored wetland have been significantly improved, but a wide gap still existed between restored wetland and natural wetland. |
PDF Full Text Request