Characteristics and influencing factors of soil CO2 release under different land use types in the typical dolomite area of humid subtropical regions

To further reveal the law of karst carbon cycle，as well as understand the characteristics and influencing factors of soil CO2 release in different land use types in the dolomites in the Huangzhouhe basin，which is the sub-basin of the Shanmuhe basin， a world natural heritage site in karst area， Shibing， southern China， in this study，the soil CO2 concentration in three different land use types （forest land， dryland， paddy field）were measured for one year.Soil samples were collected to analyze their physical and chemical properties. The results show that，（1） The annual average soil CO2 concentration in different land use types is， paddy field（21，008×10-6）> forest land（9，038×10-6）> dryland（5，660×10-6）；（2） The variation patterns of monthly soil CO2 concentration curve and monthly mean air temperature change curve of forestland and dryland in a year were similar，and annual variation law was generally consistent.The soil CO2 concentration gradually increased from January to July， and reached the peak value in August ，which was 16，157×10-6 and 13，458×10-6， respectively；（3） The CO2 concentration in paddy soil gradually decreased from January to March ， and the lowest value in March is 11，727×10-6， it gradually increased from March to December， and began to fluctuating increase in August， and reached a peak of 29，993×10-6 in October；（4） The soil CO2 concentration in dolomite area has a significant seasonal variation law of high in summer and autumn and low in spring；（5） Air temperature and rainfall have significant effects on CO2 concentration of forest land and dryland soil， but have no significant effect on the CO2 concentration of paddy field ；（6） The correlation coefficient of soil CO2 concentration corresponding to the difference of its organic carbon content is R=0.70 （P=0.03）， indicating that the difference of soil organic carbon has certain impacts on soil CO2 concentration， and the soil CO2 concentration increases with the increase of soil pH value.