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

Abstract

Abstract The autumn freeze-thaw period is an important period to influence soil carbon dynamics. However, the activities of soil CO2 and CH4 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 CO2 and CH4 fluxes in 30a, 45a, and 66a Brich forests in the Daxing'an Mountains permafrost zone, and established the relationships between soil CO2 and CH4 fluxes and soil temperature and humidity, and soil active carbon and nitrogen. The results showed that soil CO2 and CH4 fluxes of all three stand ages showed a gradual decrease during the monitoring period. Soil CO2 and CH4 fluxes showed a trend of increasing and then decreasing with stand age. The average soil CO2 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 CO2 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 CO2 and CH4 fluxes. NO3--N and MBC/N had greater effects on soil CO2 and CH4. The global warming potentials ranged from 2171.84—4132.93 kg/hm-2.