| Global warming is one of the most serious environmental problems facing mankind in twenty-first Century. Research shows, such as the rise in greenhouse gases in the atmosphere of CO2, N2O concentration is the main cause of global warming.According to estimates,80%～90% of CO2,5%～20% of N2O each year from soil, and farmland soil is the important source of greenhouse gas emissions. Forest soil respiration is an important part of the global soil carbon cycle, its’dynamic changes will produce a far-reaching impact on the global carbon cycle of forest soil, soil is also an important source of atmospheric N2O. Exist in the subtropical region of China is the world’s forest types in the same latitudes forest ecosystem characteristic, plays an important role in the global terrestrial ecosystem C, N cycle.This study is based on Chinese Academy of purple soil in Yanting agro- ecological experimental station, during the period from October 14,2012 to September 24,2014, using the static chamber- gas chromatography method for the determination of Sichuan Hilly Area in wheat- maize rotation field as well as alder and Cypress Mixed Forest Soil CO2 and N2O fluxes, analysis of soil environmental factors such as soil temperature, humidity and soil soluble organic carbon (DOC) and inorganic nutrients (NO3--N and NH4+-N) content on soil CO2 and N2O emissions. Using the observation data of farmland and forest soil CO2 and N2O on the release of the DNDC model and the Forest-DNDC model is verified. The main results are as follows:(1) Wheat-maize rotation farmland in hilly area of Sichuan as well as alder and cypress mixed forest soil are important CO2 and N2O release source, and the changes of soil CO2 and N2O emission show obvious seasonal trend. The soil CO2 and N2O emission peak appeared after the temperature change and large rainfall events, soil N2O emission peaks caused by fertilization and heavy rainfall events, and the changes of soil respiration rate depends on temperature change. In the summer of farmland and forest soil respiration and the release of N2O was significantly higher than that in winter. Farmland and forest soil average respiration rate was 41.60 and 60.15mg C m-2h-1 during October in 2012 to October in 2013.(2)The change of soil environmental factors has significant effect on soil heterotrophic respiration and N2O emission from farmland and forest land. Among them, the relationship between soil temperature and soil respiration rate of cropland and woodland can use the exponential model the R= a × eb×T to describe. A significant correlation between soil temperature, humidity and farmland and forest soil N2O emissions. Nitrate nitrogen content in farmland and forest soil CO2 release was significantly correlated, no correlation with soil N2O emissions, but does not mean that the nitrate content had no effect on the emission of N2O. The relationship between farmland and forest soil soluble organic carbon (DOC) and soil CO2, N2O emissions are available in a linear regression equation fitting. Multivariate regression analysis showed that,the main driving factors in the area of farmland and forest soil respiration is the soil temperature and humidity, the main driving factor of soil N2O emissions is soil organic carbon content,soil nitrate nitrogen and soluble organic carbon (DOC) content, the main driving factor of forest soil N2O emissions is soil DOC content.(3) DNDC model and Forest-DNDC model can better simulate the respiration of farmland and forest soil N2O emission and heterotrophic, this model can apply to study in the study area. The results of farmland and forest soil CO2 and N2O release data and field measured model is very close, RMSE is less than 15%, basically to capture the changes in temperature and several major rainfall induced soil CO2 emission peak, soil fertilization and precipitation N2O excitation peak. |
PDF Full Text Request