| Permafrost region cover approximately 25%of the Northern Hemisphere's terrestrial surface.Permafrost region stores large amounts of soil organic carbon and total nitrogen,which is an important carbon and nitrogen pool.In the context of global climate change,the permafrost region is thawing and degradation in the global scales,which would change the microbial community and microbially-mediated carbon and nitrogen cycle,resulting in lots of greenhouse gases released into the atmosphere.N2O,CO2 and CH4 are the most important greenhouse gases in the atmosphere,which are significant component of the carbon and nitrogen cycle in the high-latitude permafrost region.However,the emissions of N2O,CO2 and CH4 from forest wetlands in the permafrost region is scarce.In this study,the static opaque chamber technique was used to measure N2O,CO2 and CH4 emission from three type of wetlands in the continuous permafrost region of Daxing'an Mountains,northeast China.The objectives of this study were to(1)understand the temporal variation of N2O,CO2 and CH4 from three type of wetlands in the permafrost region during the growing season,reveal the relationship between greenhouse gas and environmental factors;(2)the effects of spring freeze-thaw cycles on N2O,CO2 and CH4 emissions,to expound the influence of environmental factor on the release of greenhouse gases in the permafrost region;(3)the difference of N2O,CO2 and CH4 flux among the three type of wetlands,reveals the key driver factors of N2O,CO2 and CH4 flux;(4)to evaluate the growing season,spring freeze-thaw period and annual emission and global warming potential in the permafrost region of Daxing'an Mountains.During the growing season,the emission of N2O,CO2 and CH4 were 11.81-79.25 ?g m-2 h-1,60.45-894.42 mg m-2 h-1 and-0.248-11.459 mg m-2 h-1 in the permafrost region of Daxing'an mountains,respectively.There was no significant relationship between N2O emission and most environmental factors.The stepwise multiple linear regression shown that the N2O emission were affected by multiple environmental factors,including air temperature,soil temperature,water table level,pH,nitrate nitrogen,total organic carbon,total nitrogen and carbon-to-nitrogen ratio.The multiple environmental factors could explain 11.49-82.84%temporal variation of N2O emission.The CO2 emission were significantly positive correlated with soil temperature in the three type of wetlands,which could explain 43.89-80.20%temporal variation of CO2 emission.The temperature coefficient of carbon dioxide was ranged from 1.18 to 1.24.The CH4 emission from the three type of wetlands were affected by different environmental factors.The XD wetland and GC wetland were significantly positive correlation between CH4 emission and soil temperature,while XT wetland was affected by water table level.Otherwise,the thaw depth of active layer could increase the release of CH4 emission in the XD wetland.The freeze-thaw cycles had significant influence on the temporal variation of N2O,CO2 and CH4 emission.The N2O,CO2 and CH4 emission were ranged from-35.75 to 74.17 ?g m-2 h-1,19.08 to 696.02 mg m-2 h-1 and-0.067 to 3.457 mg m-2 h-1,respectively.The N2O emission were affected by multiple environmental factors,including air temperature,soil temperature,soil moisture,pH,ammonium nitrogen,nitrate nitrogen,organic carbon,total nitrogen and carbon-to-nitrogen ratio.However,the driver factors were difference in the three type of wetlands.Soil temperature and thaw depth of active layer significantly affect the release of CO2 emission during freeze-thaw period.There is a significant positive correlation and exponential relationship between CO2 emission and soil temperature,which could explain 44.84-95.38%temporal variation of CO2 emission during freeze-thaw period.Similar to the growing season,the Q10 value of CO2 emission during the freeze-thaw period is range from 1.10 to 1.57.In the XD wetland and GC wetland,the CH4 emission was significantly positive correlated with soil temperature,while in XT wetland was mainly correlated with air temperature and soil moisture.Environmental factors could explain 38.53-97.37%temporal variation of CH4 emission during the freeze-thaw period.The Q10 value of CH4 emission during the freeze-thaw period is range from 1.79 to 1.86.The wetland types had no significant effect on N2O emissions both in the growing season and freeze-thaw period,which is mainly due to the low content of mineral nitrogen.The low mineral nitrogen limited the release of N2O emission in the different types of wetland,resulting in the non-significant influence of N2O emission.There had similar influence of wetland types on the CO2 emission in the growing season and freeze-thaw period.The GC wetland was significantly higher than that of XD wetland.Water table level is the key driver that caused differences in CO2 emission.During the growing season and freeze-thaw period,the CH4 emission from GC wetland was significantly higher than XD wetland and XT wetland.The water table affect the release of CH4 emission from three type of wetlands.In the permafrost region of Daxing'an mountains,the cumulative N2O flux in the growing season was ranged from 1.02 to 1.46 kg hm-2,and the annual emission ranged from 1.92 to 2.90 kg hm-2.The contribution of N2O emission from the growing season to the annual emission were ranged from 46.27 to 53.57%.The N2O emissions were released about 0.35 to 0.66 kg hm-2 during the freeze-thaw period,and its contribution rate to the annual emission were ranged from 15.86 to 32.77%.The annual CO2 emission were ranged from 10864.76 to 22205.48 kg hm-2,of which the growing season accounts for 69.95 to 77.21%,while the freeze-thaw period only accounts for 15.37 to 18.56%.The CH4 emission from permafrost region were released about 2.83 to 205.19 kg hm-2.The annual CH4 emission of GC wetland was closed to the average CH4 emission of wetland ecosystem,while that of XD wetland and GC wetland were very low.As the climate warming,the permafrost region was thawing in the global scale,which would release large amount of C from permafrost region into the atmosphere and promoted global climate change.The annual GWP from three type of wetlands were 11589.72±708.73,14708.57 ± 222.71 and 28481.46±898.25 kg CO2-eq hm-2.The growing season occupy large proportion to annual GWP,accounting for 69.02 to 79.36%.Among the three greenhouse gases,the C flux made a great contribution to GWP,while the proportion of N2O emission is only 1.20 to 6.90%.In the context of global climate change,permafrost degradation and soil temperature rise may increase GWP in the permafrost region.The study has great significance for understanding the characteristics and influencing factors of greenhouse gas release from permafrost region and evaluating regional climate change,and provides data basis for the response of greenhouse gas release from permafrost region under global climate warming. |
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