The CO₂ Flux Of Soils And The CO₂ Concentration Of Surface Layer At Arid Region In Temperate Zone

The impact of golbal warming on human survival and sustainable development is a global major issue,which goes beyond science and technology and penetrates into political, economic,diplomatic,cultural educational and other areas of society.However,there are some things unknown in greenhouse gases "sources" or "sinks" in circles of the Earth.The "missing carbon sink" mystery has not yet been answered.Compared top to the historical formation and evolution of the Earth,the history of observations research of atmospheric greenhouse gas is very short.The observation and research methods and equipment need to be improved.Human beings are actively seeking various mitigation and adaptation measures to deal with them. Therefore,in-depth study of regional characteristics of greenhouse gases is very urgent and important.A design and development of the soil surface(horizontal) and profile(vertical) of carbon dioxide in situ observation methods and devices have been carried out of the temperate,arid areas in China.Two observation sites were selected with a typical grassland in chestnut soil,desert grassland in sierozem,Elm stand in fragmental soil and chinese pine stand in gray-cinnamonic soil.The concentration in surface layers and the flux of carbon dioxide between soil surface and atmosphere with 38-point of sample have been measured and researched in situ since 2005.The main results are as follows:1.An in situ method and apparatus for measuring CO₂ flux at soil surfaceAn in situ method and apparatus for measuring carbon dioxide flux at soil surface have been carried out.The methods and devices can be used for the concentration observations of carbon dioxide at surface layer of atmosphere and the flux measurment of carbon dioxide between soil and atmosphere in situ,with spending of small,portable and easy to operate devices,and diverse points of reliable data,directly and rapid obtained.2.An In Situ Method and Apparatus for Measuring CO₂ Flux at Various Depths of Arid Soil An in situ method and apparatus for measuring carbon dioxide flux at various depths of arid soil have been carried out.The methods and devices can be used for soil CO₂ flux of observation at different depths(0-200 cm).Other values are the CO₂ storage Estimation at different soil depth,the value Estimation of CO₂ emissions caused by change of land-use and land-cover,as well as restoration of vegetation or soil fertility rate of evaluation.3.The characteristics of the carbon dioxide concentration in the surface layer of the atmosphereThis research focus on the concentration of carbon dioxide from the surface layer of atmosphere in 4 vegetations:typical grassland in chestnut soil,desert grassland in sierozem, Elm stand in fragmental soil and chinese pine stand in gray-cinnamonic soil.The background concentration of carbon dioxide is 323.49±21.36×10^-6.There are differences of the carbon dioxide concentration as the different types of vegetation:Elm stand in fragmental soil for minimum 297.92±15.56×10^-6,and the desert grassland in sierozem for maximum 331.82±19.17×10^-6.Vegetation controls the changes of carbon dioxide concentration in the surface layer of atmosphere.It is found that there are some seasonal and diurnal variations.In the seasonal variation with a trend of "S",the CO₂ concentration of 336.54±27.12×10^-6reaches a summit in November and that of 305.05±15.45×10^-6 falls to the minimum.In the diurnal variation with a trend of "valley" shape,the CO₂ concentration of 318.2×10^-6 touches the minimum at 16:00 and that of 329.0×10^-6 is up to the maximum at 24:00 or 0:00.The changes in the trend of CO₂ concentration in diurnal is opposite the changes in the trend of temperature.The key factors that influenced the the CO₂ concentration are the types of vegetation coverage,and other meteorological factors.4.The characteristics of the carbon dioxide flux from the interface of Soil - the atmosphereThis research focus on the flux of carbon dioxide from the interface of soil -atmosphere in 4 soils:chestnut soil in typical grassland,sierozem in desert grassland, fragmental soil in Elm stand and gray-cinnamonic soil in Chinese pine stand.The the average of carbon dioxide flux in four types of soil surface is 230.05μmol/m².h.The range of changes is from -147.27μmol/m².h to 2319.55μmol/m².h.The order of the flux as soil types is 351.82μmol/m².h in fragmental soil＞347.33μmol/m².h in gray-cinnamonic soil＞193.36μmol/m².h in chestnut soil＞162.37μmol/m².h in sierozem.The flux of carbon dioxide from forest soils(fragmental soil and gray-cinnamonic soil) is significantly higher than that from grassland soil(Chestnut soil and sierozem).It is found that there are some seasonal and diurnal variations in carbon dioxide.In the seasonal variation with a trend of "S" shape,the CO₂ flux of 516.79μmol/m².h comes to a summit with the release from soil into the atmosphere mainly in September,and that of -7.09μmol/m².h falls to the minimum with soil absorption from the atmosphere to the soil. The trend of carbon dioxide flux in season is basically the same with the trend of climate change in local,and the trend of the carbon dioxide flux is slight later then the trend of climate change.In winter,a phenomenon of absorption(-7.09μmol/m².h),appears in each soils in January.This change will reduce and regulate the cabon dioxide concentration of atmosphere.In the diurnal variation with "mountain" shape,the CO₂ flux of 154.13μmol/m².h is smallest at 4:00 and that of 154.13μmol/m².h is the maximum at 12:00.The changes trend of CO₂ flux in diurnal is as follows,as the climate change with turn of day and night,and the trend of the carbon dioxide flux is significant later then the trend of climate change.It is found that environmental factors affect the flux of carbon dioxide.Air temperature in soil surface,soil temperature(0-10 cm,10-20cm and 20-30 cm) and soil moisture(0-10 cm) is positively related to the carbon dioxide flux in soil surface.And the soil moisture in 10-20 cm and 20-30 cm depth is negatively related to the flux of carbon dioxide in soil surface.There is not significantly different between the air relative humidity in the soil surface and the carbon dioxide flux.During the winter,it is not found that the snow absorbs carbon dioxide in the atmosphere.5.The characteristics of the carbon dioxide flux from the Soil profileThe carbon dioxide flux from the soil profile is observed and researched in 4 soils: chestnut soil,sierozem,fragmental soil and gray-cinnamonic soil.It is found that the carbon dioxide flux from Soil profiles change with the general trend of increased depth of soil.There are different rates of carbon dioxide in different soil types.In chestnut soil on the typical grassland soil,there is a downturn when soil calcium plot of the encounter occurred.In gray-cinnamonic soil on Chinese pine stand,there are two downturns,not only in the soil calcium plot,but in the mother layer of the soil.It is also found that soil texture takes part in the change and size of the carbon dioxide flux in soil profiles.There is not significant correlation between the flux of carbon dioxide and the air humidity.In summary,there is a complexity in researching carbon dioxide concentration,flux of carbon dioxide.And there are other more relative factors,including vegetation,soil type, soil texture,and weather involving the biosphere,pedosphere,lithosphere,hydrosphere between the material,energy and information exchange.The research of concentration and flux of carbon dioxide is a long-term, comprehensive history of the evolution process,which revealed the need for a longer period of time of the observation and research and repeated verification.Observation equipment also needs automated devices,as these will be further research and improvement.