Temporal and spatial distributions of CO2 in soil and their influencing factors under different LUCC: A case study of the Dalongdong underground river drainage area

The objective of this work is to further understanding the temporal and spatial distribution characteristics of CO2 in soil and its influencing factors under different land use and cover change (LUCC). We choose four types of land usage including forest land, grassland, maize land and tobacco leaf land in the Dalongdong underground river drainage area of western Hunan as examples to observe CO2 concentration of soil under these land usage conditions for one year. The results show that the soil CO2 concentrations are of the following sequence: grassland (7,527 mg·m-3)> forest land (7,197 mg·m-3)> tobacco leaf land (4,562 mg·m-3)> maize land(4,414 mg·m-3). With increasing depth of profiles, the soil CO2 in grassland and maize land usage rises first (at 10-30 cm depth) and then is stabilized (at 30-50 cm depth), and the forest land and tobacco leaf land show a trend of increasing first (at 10-30 cm depth) and then decreasing(at 30-50 cm depth). Monthly change curves of them show that the concentration of soil CO2 increases from February to August, decreases from August to December, and decreases slightly from December to February of next year. The lowest and highest values of soil CO2 concentration occur in February and August, respectively. The correlation analysis also indicates that the effect of temperature on the soil CO2 concentration is the most significant. In addition, the difference of organic carbon under different land use and the rainfall factor coupled with the temperature can pose major influence on the change of soil CO2 concentration.