| The research on "missing sink" is main content in the global carbon cycle and global climate change .The research on the carbon cycle show that the "missing sink" is the part of terrestrial ecosystem, such as soil. Soil CO2 concentration is origin from live shoot, live root .soil microbial and carbon dioxide in the Earth atmosphere . The CO2 concentration in karst soil is greater than that in the Earth atmosphere. Its absorption and emission are affecting Carbon dioxide in the Earth atmosphere. The research on dynamics of soil CO2 concentration is very important to research on the dynamics of atmospheric CO2 The atmospheric CO2 concentration in the karst district is lower than other districts. But soil CO2 concentration in the karst district is greater than other districts. The sources and sinks of atmospheric CO2 are becoming chief problem in the carbon cycle. People pay more attention to daily and seasonal variation in soil CO2. However, they seldom focus on karst districts.We took the karst experimental site of Jinfo mountain nature reserve area as example. We select four experimental sites-grassland, forest .the bare land and Chimonobambusa to carry out the research. The research include: 1) measuring CO2 concentration in the soil air and vegetation air by using CO2 measuring instruments; 2) measuring the releasing rate of CO2 coming from soil surface byusing alkaline absorbing method; 3) measuring the hydrochemical indexes of soil water . The research results are as follows:(1) The author has made field observation of depth distribution of soil air CO2 in the Mt.Jinfo Karst Experiment Site. The results show that two concentration gradient, soil to atmosphere and soil to carbonate rock, are form. In the interface of soil and atmosphere, the COj in the soil release to the atmosphere. But variation of the CO; concentration in the bottom soil show that sink effect of carbonate rock on the soil air CO2(2) The diurnal observation results of soil CO2 dynamics in the different vegetation show that the soil CO2 concentration in the bare land is sensitive to environment, but the soil CO; concentration in the other experimental site, which covered with vegetation, restrain the variation.(3) The diurnal observation results of soil CO2 dynamics in the field display the variation of soil CO2 concentration and the releasing rate of CO2 coming from soil surface is controlled by temperature .The correlation between CO2 concentration in the top soil and temperature is very significant. But the correlation between CO2 concentration in the bottom soil and temperature is not significant. On the other hand, the change of the release amount of CO2 was same that as the temperature. So, the temperature is main factor determining change law of the release amount of CO2 from soil and its rising and falling bring out the increase and decrease of release amount of CO2 The correlations between CO2 in the atmosphere and the release amount of CO2 were very significant.(4) The result shows that the CO2 concentration in the soil is sensitive to the rainfall. The soil CO2 dynamics response to rainfall in the soil section was regular migration process: one gradient with up-high and down-low before rainfall-two gradient with up and down high and middle - low from the beginning rain -one gradient with up-high and down-low .The intensity of rainfall will influence the CO2 concentration in the soil. The CO2 concentration in the soil will rise in the rainfall. But rainwater wad filled in the soil holes and form thin water - layer,which force the soil CO2 to transfer to bottom and accumulation. The change of CO2 concentration after precipitation within vegetation demonstrates CO2 concentration in the vegetation impacted by rainfall and deposition in the rainfall.(5) The observation results of atmospheric CO2 concentration in the field display the sink effect of karst soil on atmospheric CO2 .The result of the correlation between CO2 vegetation air and the releasing rate of CO2 coming from soil surface s...
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