Study On The Dynamics And The Main Influencing Factors Of CO₂ Emission In A Changbai Mountain Peatland

Studying the dynamics of carbon dioxide（CO₂）fluxes in peatlands in the context of climate change and their responses to environmental changes has been one of the hot spots in wetland science research,aiming at understanding the process of wetland carbon cycle and the stabilization mechanisms of ecosystems,in order to exert their ecological effects in response to climate change.Northern peatlands have persisted as small carbon sinks,and they are very sensitive to environmental changes.In this study,we used the eddy correlation technique to analyze the variation of CO₂ fluxes and the main influencing factors in three years with increasing temperature in a typical peatland in Changbai Mountains;We used chamber and high-throughput sequencing technology to investigate the influence mechanisms of different snow cover on CO₂ fluxes by setting three snow depths of 0 cm,60 cm and 90 cm in winter;We measured the contents of light-fraction organic carbon（LFOC）,dissolved organic carbon（DOC）,microbial biomass carbon（MBC）and easily oxidizable carbon（EOC）in different seasons.Elastic network regression models and structural equation models were used to reveal the contributions of different soil organic carbon fractions to the seasonal changes of soil organic carbon（SOC）and CO₂ fluxes,and this study preliminarily clarified the response mechanisms of CO₂ fluxes to environmental changes in the study area under the condition of increasing temperature.The main findings of this study are as follows:1.The daily,seasonal and annual variation of net ecosystem exchange（NEE）in the growing season showed a"U-shaped"curve,while ecosystem respiration（ER）and gross primary productivity（GPP）showed an inverted"U-shaped"curve.There was an interannual variation in NEE,study area in 2018 and 2019 showed as a carbon sink,the cumulative carbon sinks were 311.52 g C m^-2 yr^-1and 302.38 g C m^-2 yr^-1,respectively.However,2011 showed as a carbon source,the cumulative carbon source was 57.04 g C m^-2 yr^-1.NEE is mainly regulated by ER and GPP,the differences of carbon sink function in different years mainly occurred in the peak growing season of plants,which was due to the different water and heat conditions in the growing season.GPP is related to the start and duration of the growing season,photosynthetically active radiation,and varied with plant phenology.Temperature is the main factor affecting ER,precipitation and water level mainly affect the interannual NEE.In 2011,the wetland ecosystem in the study area converted from a carbon sink to a carbon source,mainly because of the higher ER caused by lower water level.CO₂fluxes fluctuated during the non-growing season,and"CO₂pulse"occurred after the snow was melt.And CO₂ fluxes were significantly correlated with snow depths,but there was no significant correlation between CO₂fluxes and snow depths when snow depths were shallow.2.The results of the snow depth gradient control experiment showed that during the snow cover period,the snow cover had a blocking effect on the emission of CO₂ from the wetland to the atmosphere,thus reducing the CO₂ fluxes;However,after the snow melt,CO₂ fluxes increased by 0.75 g·cm^-2·s^-1 and 0.46 g·cm^-2·s^-1 in the 60 cm and 90 cm treatment groups,respectively,significantly higher than that in the treatment group without snow cover.This effect of snow cover was associated with a significant increase in soil temperature,which allowed the presence of liquid water around the soil particles.This warming effect of snow cover ensured the activities of soil enzymes and soil microorganisms,attenuated the negative effects caused by low temperatures,increased the diversities of bacterial communities,and provided more ecological niches for microorganisms that can resist dehydration and low temperature environments.3.The results of the study confirmed that DOC and LFOC are important fractions in the carbon cycle process.The contributions of LFOC to SOC is positive,consistent with the seasonal variation of SOC.However,there were some seasonal differences in the labile organic carbon fractions that mainly contributed to the SOC changes,among which,MBC was the main organic carbon fraction that played a major role in winter.The effects of different environmental factors on soil organic carbon pools have direct and indirect effects.Soil p H directly affected soil carbon pools,while soil temperature indirectly affected soil organic carbon by affecting soil microorganisms;Combined with the results of high-throughput sequencing and correlation analysis,it was found that phospholipid fatty acids of the subsoil and the soil fungal composition might play a key role in the soil carbon cycling process.In summary,among the effects of environmental factors on ecological processes and functions of peatlands in cold regions,temperature was an important environmental factor affecting NEE,although precipitation and water level were not the limiting factors for net carbon exchange during the growing season,they were key factors for interannual variation of carbon sink/source in wetlands,and can even change the source/sink function of wetlands;The isolation and warming effects of snow cover can reduce the negative effects of low temperature on the activities of soil microorganisms,ensure the normal soil biochemical processes,and play an important role in wetland carbon cycle of non-growing season;DOC and LFOC might have the potential to influence the carbon cycle of wetlands in cold regions.This study deeply explored the response mechanisms of soil-atmosphere net carbon exchange in peatlands at different time scales to climate change and the factors influencing interannual carbon flux dynamics,which can provide scientific supports for understanding the transformation and mechanisms of wetland carbon sink/source and the function of wetland ecological services,and it is valuable and instructive for the scientific management of wetland.