Characteristics of soil CO2 and CH4 fluxes in birch forests during the autumn freeze‒thaw period in the permafrost region of the Daxing′an Mountains, Northeast China

The autumn freeze-thaw period is an important period to influence soil carbon dynamics. However, the activities of soil CO 2 and CH 4 in different stand ages of birch forests in high latitude perennial permafrost regions of China during this period are not clear. Therefore, in this study, we investigated soil CO 2 and CH 4 fluxes in 30a, 45a, and 66a Brich forests in the Daxing'an Mountains permafrost zone, and established the relationships between soil CO 2 and CH 4 fluxes and soil temperature and humidity, and soil active carbon and nitrogen. The results showed that soil CO 2 and CH 4 fluxes of all three stand ages showed a gradual decrease during the monitoring period. Soil CO 2 and CH 4 fluxes showed a trend of increasing and then decreasing with stand age. The average soil CO 2 flux of 30a (19.24±4.03) mg·m -2 h -1 was the lowest throughout the monitoring period and was significantly smaller than that of the other two stand ages ( P <0.05). 45a and 66a had average soil CO 2 fluxes of 36.44±5.20 mg·m -2 h -1 and 35.49±4.22 mg·m -2 h -1 , respectively, which were not significantly different from each other ( P >0.05). The average uptake fluxes of 45a (-25.92±3.55) μg·m -2 h -1 > 66a (-24.73±4.01) μg·m -2 h -1 > 30a (-12.22±2.33) μg·m -2 h -1 , and 30a was highly significantly smaller than 45a and 66a ( P <0.01), and the difference between 45a and 66a was not significant ( P >0.05). Soil temperature and moisture were both highly significant on soil CO 2 and CH 4 fluxes. NO 3 - -N and MBC/N had greater effects on soil CO 2 and CH 4 . The global warming potentials ranged from 2171.84—4132.93 kg/hm -2 .