Global warming will increase the greenhouse gas (GHG) fluxes of permafrost regions. However, little is known about the difference in GHG fluxes among different types of permafrost regions. In this study, we used the static opaque chamber and gas chromatography techniques to determine the fluxes of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in predominantly continuous permafrost (PCP), predominantly continuous and island permafrost (PCIP), and sparsely island permafrost (SIP) regions during the growing season. The main factors causing differences in GHG fluxes among three types of permafrost regions were also analyzed. The results showed mean CO2 fluxes in SIP were significantly higher than that in PCP and PCIP, which were 342.10 & PLUSMN; 11.46, 105.50 & PLUSMN; 10.65, and 127.15 & PLUSMN; 14.27 mg m(-2) h(-1), respectively. This difference was determined by soil temperature, soil moisture, total organic carbon (TOC), nitrate nitrogen (NO3--N), and ammonium nitrogen (NH4+-N) content. Mean CH4 fluxes were -26.47 & PLUSMN; 48.83 (PCP), 118.35 & PLUSMN; 46.93 (PCIP), and 95.52 & PLUSMN; 32.86 & mu;g m(-2) h(-1) (SIP). Soil temperature, soil moisture, and TOC content were the key factors to determine whether permafrost regions were CH4 sources or sinks. Similarly, PCP behaved as the sink of N2O, PCIP and SIP behaved as the source of N2O. Mean N2O fluxes were -3.90 & PLUSMN; 1.71, 0.78 & PLUSMN; 1.55, and 3.78 & PLUSMN; 1.59 & mu;g m(-2) h(-1), respectively. Soil moisture and TOC content were the main factors influencing the differences in N2O fluxes among the three permafrost regions. This study clarified and explained the differences in GHG fluxes among three types of permafrost regions, providing a data basis for such studies.

Autumn freeze-thaw period significantly influenced the soil temperature, moisture, nutrients, and then affected the structure and diversity of soil microbial community. In this paper, three types of wetlands in the permafrost region of Daxing' an Mountains were selected to investigate the greenhouse gas fluxes during the autumn freeze-thaw period. CO2, CH4 , and N2O fluxes during the autumn freeze-thaw period ranged from 24.76 to 124.06 mg m(-2) h(-1),-249.10 to 968.87 mu g m(-2) h(-1), and - 4.21 to 12.86 mu g m(-2) h(-1). CO2 fluxes were mainly influenced by soil temperature and moisture. CH4 fluxes were mainly influenced by temperature and soil moisture. And N2O fluxes were significantly affected by temperature, soil moisture, ammonia nitrogen, and nitrate nitrogen. Environmental factors could explain 64-73.2%, 51-85.4%, and 60.3-93.3% of temporal variation of CO2, CH4, and N2O fluxes, respectively. Comparing different wetlands, the soil temperature was the significant factor to affect the CH4 flux. The global warming potentials during the autumn freeze-thaw period ranged from 717.83 to 775.57 kg CO2-eq hm(-2).

Forest fires lead to permafrost degradation and localized drought, and regional droughts increase the probability of forest fires, leading to a positive feedback loop between climate change and fires. However, the relationship between fire occurrence and climatic factors change is unclear for boreal forests, which represent the largest land-based biome and stock of carbon. Here, we analyzed the relationship between lightning fire occurrence and meteorological and topographic factors based on the fire frequency, burned area, and meteorological data from the primeval forest region of the northern Daxing'an Mountains in China. We found that lightning fires occurred most frequently at an altitude of 600 to 700 m. From 1999 to 2019, the frequency of lightning fires showed an overall upward trend, whereas the affected area had no obvious change. It can be attributed to fire suppression efforts and greatly increased investment in fire prevention in China. Snow cover had a strong regulatory effect on the start and end dates of lightning fires for seasonal cycle. The frequency of lightning fires was positively correlated with the average temperature, maximum temperature, and surface evaporation and negatively correlated with precipitation and surface soil moisture (0-10 cm). The result will be useful in the spatially assessment of fire risk, the planning and coordination of regional efforts to identify areas at greatest risk, and in designing long-term lightning fires management strategies.