Emission of CO_2, CH_4 and N_2O from freshwater marsh during freeze-thaw period in Northeast of China

摘要

The freeze-thaw period, 7-8 months in Sanjiang Plain, influences the greenhouse gases fluxes greatly. The static chamber technique aided by gas chromatogram was used for investigating characteristics of emission of CO_2, CH_4 and N_2O from freshwater marsh wetlands located in the Sanjiang Plain. The results showed that there were obvious CH_4 and CO_2 emissions in winter and the CH_4 emission made a relatively large contribution to the total CH_4 flux in the different type freshwater marshes during winter in Sanjiang Plain. And there were significant CH_4 and CO_2 emission peak values during thawing time. The CH_4 and CO_2 emissions from freshwater marsh seasonal flooded were larger than that from freshwater marsh continuously flooded during thawing time. On the contrary, the CH_4 and CO_2 emissions from freshwater marsh continuously flooded were larger than that from freshwater marsh seasonal flooded in winter. During thawing, there was exponential relationship between CO_2 fluxes and the soil temperature (5cm) (R~2 = 0.912, P<0.001). Meanwhile, ecosystem respiration was obviously correlated with the CH_4 fluxes (R~2 = 0.751, P<0.001). We found that the freshwater marshs were N_2O sink in winter and gradually became N_2O source, with increasing temperature during thaw. The characters of the greenhouse gases emission, during freeze-thaw in the Sanjiang Plain, responded to the microbial activity in winter and the effects of thawing on soil carbon mineralization, nitrification and denitrification.