Comparison Of Soil CO₂Efflux Rate Among Four Typical Subtropical Forests In Hilly Areas Of Mid-subtropical, China

Soil is the largest carbon (C) pool in terrestrial ecosystems. Carbon storage in soil pool accounts for about1300-2000PgC, which is2-3times of vegetation C pool and more than2times of the atmospheric C pool. The C storage in the forest soil accounts for73%of the global soil organic C, soil is the important sink of atmospheric CO2. Just because of the enormous capacity of reservoir of the soil C, a small amount change in soil C may influence the discharge from soil C pool to atmosphere. A large amount of researches indicate that the influences of the soil organic C release is as important as the influences that industry discharges CO2to the atmosphere, influences the global climatic change with the greenhouse effects, influences the nutrient supply of the vegetation of land too, and then produces deep influences on the distribution, composition, structure and function of the ecosystem of land; meanwhile, the greenhouse effects will promote the losses of the soil organic carbon conversely.Soil CO2efflux in four forests(Cunninghamia lanceolata, Pinus massoniana-Lithocarpus glaber, Choerospondias axillaris, Cyclobalanopsis glauca) in hilly areas of central Hunan, China,from August2010to July2011, were investigated by using static chamber to sample released gas from soil for chemical analysis with gas chromatography. The influences of forest type, seasonal dynamics and soil moisture on soil CO2efflux were investigated.The results are as fellows:(1) The maximum flux occurred in July and the minimum flux occurred in February. seasonal variations of soil respiration rate were from34.73-350.48mg.m-2.h-1in C. lanceolat, from62.03-278.98mg.m-2.h-1in P. massoniana, from52.11-285.95mg.m-2.h-1in C. axillaris, from51.95-278.5mg.m-2.h-1in C. glauca; The average rates of soil CO2efflux in four forests was the highest for C. axillaries forest (157.99mg.m-2.h-1), immediate for C. lanceolata plantation (151.25mg.m".h-1) and C. glauca forest (144.75mg.m-2.h-1), and the lowest for P. massoniana forest (142.19mg.m-2.h-1).(2) The four forests had significant different seasonal change patterns of soil respiration processes. C. axillaris, P. massoniana and C. exhibited irregular fluctuated curves during the study period. The greatest significant correlation were found between soil efflux and soil temperature (within the depth from0to5cm depth, from5to10cm depth, respectively) in four forest types (p<0.001). However, there were no significant for the correlation between soil CO2efflux and forest type, soil moisture (p=0.09).