| With the situation of atmospheric CO2 concentration elevating, carbon cycle has been one of hot topics in the world. Soil carbon pool is an important component of the global carbon cycle, and it has direct effects on the global carbon balance. Karst area is occupied 12% the area of all land in the world and 1/3 land of China, karst area is an important part of the earth surface system. There is 99.55% carbon of the earth combined with carbonate rock.. Moreover, recently research shows the modern karst process closely connects with the global carbon cycle. Soil active organic carbon refers to the fractions of organic carbons that are easy to move and to be oxidized and mineralized, and they are quite available to plant and soil microorganisms. Soil dissolved organic carbon (DOC) and microbial biomass carbon (MBC) are considered to be the useful indicators of active organic carbon. Soil active organic carbon is involved in all biological and biochemical processes in soil, the minor change of active organic carbon can be detected before the content of total organic carbon (TOC) in soil has changed, although it accounts for small fraction of TOC.The soil active organic carbon accelerated karst erosion because of its acid and chelation. Thus soil active organic carbon was important to karst dynamic system. In addition, soil organic pool released CO2 to the sky through soil respiration, so soil respiration was the main way in carbon flow ways. So study soil active organic carbon and soil respiration was signification on the research of soil carbon cycle.The research took the karst and non-karst soils of Mao village for research objects, by compared karst region with non-karst region in the same climate zone, on the migration and transformation of soil carbon way, observing the dynamic change in time intervals to soil active organic carbon and soil respiration. It took two years to collect dada by field monitoring and experimenting and carbon stable isotope.The study results showed that:1,The DOC content in karst soils were far less than in non-karst soils due to neutral and partial alkaline of pH value, high content of humus acid in organic matter, because humus acids react with the high content of calcium and magnesium ions in karst soils and thus the formation of stable compounds. The average content of DOC in non-karst soils were 7.62 times higher than that in karst soils in the depth of 0~20cm, and the content of DOC in non-karst soils were 6.30 times higher than that in karst soil in the depth of 20~50cm. DOC content had the highest value in autumn, and decreased with the increasing of soil depth in spatial distribution in two kinds of soils.2,The MBC content in karst soils (the average value: 716.75mg.kg-1) were higher than that in non-karst soils (the average value: 573.66mg.kg-1) in the depth of 0~20cm. It may due to the higher content of SOC and nutrient elemental was favor to microbial biomass growing. In addition, the content of MBC had decreased with the increasing of soil depth in spatial distribution in two kinds of soil. Moreover, the seasonal effects of MBC content was no significant difference for two kinds of soils.3,The monthly dynamics of soil active organic carbon had the same trend in the two soils, they were can be divided into four stages: (1) September to November, MBC content had big fluctuation, and DOC had the highest value in the year with high temperature, less rainfall and increasing plants litters;(2) December to January, the content of soil active organic carbon were lowest in the year, because the temperature dropped quickly, the activity of microbial biomass fell;(3) February to April, the concentration of soil active organic carbon increased with temperature rising, rainfall more frequently and all lives coming round;(4) from May to August, it was hot and rainy, DOC was decomposed by microbial biomass and part of DOC lost with water at heavy rainfall, so the DOC content in soil was not high.. The soil microbial biomass carbon turnover rate was fast in this period, so the MBC content was in low level.4,The content of DOC had positive correlation to the content of soil temperature in two soils; The content of MBC was weak negatively correlated to the content of water in soil. Relationship between DOC and water content were negative in two soils, especially in non-karst soil had remarkable negative relation(r=-0.448**,sig.<0.01). The content of DOC had negative correlation to pH value in karst soil, but the relationship was weak in the non-karst. The content of MBC had weak negative correlation to pH value in two soils. Relationship between DOC in karst soil and HCO3- in spring was remarkable positive , but the relationship was negative in DOC and dissolution rate of test-slices in karst region. The correlation was better in karst than in non-karst region between MBC content and HCO3- in spring.5,The results of research show that the value of soil respiration in karst soil(the average value: 118.81 mgC.m-2.h-1 )was obvious smaller than that in non-karst soil(the average value: 156.99 mgC.m-2.h-1 ), and the regular of seasonal changes were Summer>Spring>Autumn>Winter, in addition, value of soil respiration in Summer was 2.66-4.81 times higher than that in Winter.6,The best fitting function was exponential function model between soil respiration and soil temperature. The fitting equations were: karst soil y=189.45e0.084T (p<0.01)and non-karst soil y=200.82e0.059T( p<0.01),and the value of Q10 were 2.33 and 1.82 ,respectively. The response was more sensitive of soil respiration and environment changes in karst soil than that in non-karst soil. In addition, theδ13C values of CO2 emissions from soil respiration in karst soil were heavier than that in non-karst soil, and appeared the corresponding relationship between light carbon and high temperature or heavy carbon and low temperature.7,Soil CO2 concentration at different depth in karst soil changed from low to high and then to low and then turn to high at bottom, the wavy trend looked like deviated"N"shape. Soil CO2 concentration increased obviously with soil depth in non-karst soil. In addition, the highest concentration of soil CO2 mainly appeared at bottom in the karst profile in Winter and Spring, and it had a trend to migrate to subsoil in Summer and Autumn. The concentration of soil CO2 in non-karst soil was 1.65-7.54 times higher than that in karst soil because of the special karst environment.Research conclusions:1,The DOC concentration in karst soil was far less than that in non-karst soil.2,The MBC concentration in karst soil was obvious higher than that in non-karst soil.3,The value of soil respiration in karst soil was obvious lower than that in non-karst soil. The fitting function between soil respiration and soil temperature results showed that ,the response was more sensitive of soil respiration and environment changes in karst soil than that in non-karst soil.4,The concentration of soil CO2 in karst soil was far less than that in non-karst.
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