[Dynamics of CO2, CH4 and N2O emission fluxes from mires during freezing and thawing season].

In the Sanjiang Plain, the freezing and thawing phase have 7 - 8 months and play important role in the greenhouse gases emission. The characters of the greenhouse gases emission during freezing and thawing season in the Sanjiang Plain were studied, using the static chamber and gas chromatogram method. The results observed show that there were obvious CH4 and CO2 emissions in winter and the CH4 emission made a relatively large contribution to the total CH4 flux from the different type mires during the winter in the Sanjiang Plain. And there were significantly CH4 and CO2 emission peak values during thawing time. The CH4 and CO2 emissions fluxes from seasonal flooded mire were larger than that from continuously flooded mire during thawing time. On the contrary, the CH4 and CO2 emissions from continuously flooded mire were larger than that from seasonal flooded mire in winter. During thawing, there was exponential relationship between CO2 fluxes and the soil temperature (5cm) (R2 = 0.912, p< 0.001). Meanwhile, CO2 fluxes was obviously correlated with the CH4 emission fluxes (R2 = 0.751, p < 0.001). The mires are N2O sink in winter and gradually become N2O source, with increasing temperature during thawing time. The characters of the greenhouse gases emission, during freezing and thawing in the Sanjiang Plain respond to the microbial activity in winter and the effects of thawing on soil carbon mineralization, nitrification and denitrification.