|其他摘要||Soil respiration is a major component of the global terrestrial carbon cycle. An incubation experiment with three treatments (soil only, and soil mixed with 1.25% and 2.5% of maize straw) was established in early October, 2011, on bare ground in the Yanqi Basin simulating of field straw returned. CO2 efflux and soil CO2 concentration at different depths were recorded from June, 2012 to January, 2013. Diurnal and seasonal variations of CO2 efflux and soil CO2 concentration were determined. The relationship between temperature, CO2 efflux and soil CO2 concentration were analysed using various Regression analysis methods.
The results indicated that there was obvious diurnal variation of CO2 efflux under all three treatments. The maximum rate of CO2 efflux occurred during 12:00~16:00 (local time), the minimum during 5:00~7:00.On average, the total amount of carbon released during daytime accounted for about 58% ~70% of that for the whole day. There were strong seasonal variations of CO2 efflux under all three treatments, showing peaks in middle to late July and/or middle to late August and the minimum values occurred in winter.
There was also obvious diurnal and seasonal variations of soil CO2 concentration at 10 cm、20 cm、30 cm and 50 cm. The maximum soil CO2 concentration was found between 19:00~21:00 at 10 cm, 0:00~3:00 and 9:00 at 20 cm、30 cm and 50 cm, respectively, and 7:00 near the surface. The peak of soil CO2 concentration was lagged by one hour at 10 cm, comparing with that of soil temperature. The peaks of soil CO2 concentration at 20 cm and 30 cm were lagged by five hours relative to soil temperature. Over the seasonal cycle, soil CO2 concentration peaked in early July and/or middle to late August. Soil CO2 concentration was higher with straw addition than without at all depths, and showed an increase with depth. The gradient of soil CO2 concentration over depth showed a decrease with depth. The minimum gradient of soil CO2 concentration was found in November, and the maximum in June and/or September.
There were exponential relationships between CO2 efflux and soil surface temperature for all three treatments, which were highly significant in autumn (R2 >0.9, P<0.01), significant (R2 >0.4, P<0.05) of soil with straw and not significant (R2=0.287, P>0.05) of soil only in winter, but not significant in summer (P>0.05), highly significant during the whole observation. There were exponential relationships, a linear and nonlinear relationships between soil CO2 concentration and soil temperature at 10、20、30 cm soil for all three treatments, which were highly significant in autumn (R2 >0.9, P<0.01) and at 20、30 cm soil in summer (R2 >0.4, P<0.05), but not significant at 10 cm in summer (P>0.05), significant at 10 cm soil and highly significant at 20、30 cm soil for all three treatments. There were linear relationships between CO2 efflux and soil CO2 concentration at 10、20、30 cm soil for all three treatments, which were highly significant during the whole period.|