The Migration And Change Characteristics Of The Soil CO₂, And Karst Effects In Karst Region In Panlong Cave, Guilin

At present, with the situation of atmospheric CO2 concentration elevating and the greenhouse effect intensifying, carbon cycle has been one of hot topics in the world. One of the soil carbon pool is an important component of the global carbon cycle, and it has directly effects on the global carbon balance. And that karst area is occupied 12% the area of all lands in the world and 1/3 land of China, karst area is an important part of the earth surface system. Therefore, studying the migration and chang regularity of the soil CO2, and karst effects in karst region can contribute to find out the carbon cycle model, and it was helpful to karst dynamic system. In addition, soil released CO2 to the atmosphere through soil respiration, and it plays an important role in of atmospheric CO2 source and absorb effect, so soil respiration was the main way in carbon flow ways. So, in order to reveal the soil carbon cycle in karst ecological system and the mechanism research, study the migration and chang regularity of the soil CO2, and karst effects in typical karst region was significant on the research of soil carbon cycle.Since December 2009 to December 2010, using the karst experimental site Panlong Cave in Guilin as the example and chosing two plots in the scrub brush of slope and depression in karst areas, this research had tested the spatial distribution and seasonal variation of CO2 concentration, and slao the daily variation and the changes by different spaces of soil CO2 emission had been monitored in a long time (half a month time, more than a year). Analyzing the migration and change rule of soil CO2 in Epikarst, so as to reveals the karst dynamic mechanism of soil CO2 with Epikarst karstification, and the source, absorbing effect of karst-soil CO2 with atmospheric CO2. The results showed that: (1) In the two plots, the soil CO2 emission rate is greater in the deep soil than that in the top soil in spring and summer, and it's opponent in autumn and winter and also the emission rate is greater in hillside than that in the karst depression; the soil CO2 emission rate had related with the soil temperature and soil water content; The soil CO2 emission rate had seasonal variation obviously, in summer(June to September), the soil CO2 concentration is one or three times than that in the other periods, and it showed a close relation with the temperature, soil moisture content and biological activities.(2) The soil CO2 concentration had seasonal variation obviously with a trend of highest in summer and lowest in winter, in summer (May to August), the soil CO2 concentration is two or three times than that in the other periods, and it showed a close relation with the temperature, precipitation and biological activities. And it was higher in the deep soil than that in the surface and the depressions than the slope, especially in summer the soil CO2 concentration of the depression had high nearly 1000 mg/m2 than slope.(3) In the vertical soil profile, the soil CO2 concentration was increasing with soil depth increases in most cases, but the CO2 concentration of slope (-50 cm and 80 cm) and depression (-80 cm and -100 cm) all were reducing with soil depth increases during the rainy season, so named it two-way change.(4) The rate of limestone dissolution was positively correlated with the soil CO2 concentration, and also had seasonal variation obviously for spring and summer the erosion was huge and small in autumn and winter; the trend of dissolution intensity had the soil CO2 concentration was almost uniform in different soil depths, overall when CO2 concentration increased, the dissolution rate increased, it indicated that the soil CO2 concentration and time of soil water residence was the two key factors that the driving the karstification.(5) Theδ13C value of soil organic carbon has obvious change in different seasons, but the change rule of slope, depression and grassland has inconsistent; From surface to downward, the soilδ13C value has more positive with the increase of soil depth, and theδ13C value of depth soil has stable; the two kind of advantage plant,both Vitex negundo and Loropetalum chinense their average 813C value of every parts have range for -25.15‰～-28.23‰; And Theδ13C value of soil organic carbon has soil organic carbon range for -19.00‰～-22.32‰, indicated that the 813C value of soil the organic carbon has obviously higher than theδ13C value of local plants.