| Methane is an important greenhouse gas,and natural wetlands are the largest source of atmospheric methane.Carex peatlands is an important wetland type.The microtopography in Carex peatlands is widely developed,and its unique surface morphology directly affects the material circulation and energy flow process in the peatlands.In the Carex peatlands,the hummock-hollow microtopography makes the soil temperature(ST),water level(WL),vegetation type and other factors show certain micro-pattern differences,which may directly affect the release of CH4 in the peatlands.The aim was to learn the production,oxidation,transport and release of methane and what are the mechanisms that affect methane release at a Carex peatland in Changbai Mountains,located in northeast China.The study site was a sedge peatland.Gas samples of emitted CH4 were drawn from hummocks,under hummocks and hollows using a closed chamber method to analyze CH4 flux.Soil samples for soil factors analyze were collected at the depth of 0?30cm to analyze soil organic carbon,dissolved organic carbon,total nitrogen,total phosphorus,the number of methanogens and methanotrophs,etc.Pore water samples for gas analysis were collected at the depth of 0?30cm to analyze?CH4,?CO2 and dissolved methane concentration.In addition,water table levels and peat temperatures were measured at each microtopography locations.The main conclusions are as follows:(1)In the Carex schmidtii peatlands,environmental factors at different microtopography locations(hummocks,under hummocks and hollows)have significant spatial heterogeneity.The analysis of variance showed that among the non-biological factors,the soil organic carbon(SOC)and dissolved organic carbon(DOC)in hummocks were significantly higher than under hummocks and hollows(p<0.05),while the total nitrogen(TN)and total phosphorus(TP)in hummocks were significantly lower than under hummocks and hollows(p<0.05).The microbial biomass carbon(MBC)in under hummocks was significantly higher than hummocks and hollows(p<0.05).Among the biological factors,the number of methanogens(MPB)in hummocks was significantly higher than under hummocks and hollows(p<0.05).The unique morphological structure of the hummock-microtopography makes the microclimate of different geomorphic locations appear different,which leads to the spatial and temporal heterogeneity of soil factors in different geomorphic locations and soil depths.(2)There were spatial differences in soil CH4 production pathways in the Carex schmidtii peatlands.The main way to produce CH4 in the Carex schmidtii peatlands was acetic acid fermentation.Due to the perennial flooded environment and high organic carbon content,the acetic acid fermentation reaction was promoted,and the contribution rate of acetic acid fermentation to methane production in under hummocks was higher than hummocks and hollows.The contribution rates of CH4 production by acetic acid fermentation were 49.84%-77.23%,57.28%-87.33%and 42.35%-69.78%,respectively.The contribution rates of CH4 production by H2/CO2 reduction pathway were 22.77%-50.16%,12.67%-50.16%and 30.22%-57.65%,respectively.(3)In the Carex schmidtii peatlands,the soil CH4 production rate and oxidation rate had obvious spatial heterogeneity,and the CH4 production rate and oxidation rate in hummocks were significantly higher than under hummocks and hollows(p<0.05).The rate of CH4production and oxidation in hummocks was higher,and its maximum CH4 production rate was 11 times of under hummocks and 16 times of hollows,and its maximum CH4 oxidation rate was 4.15 times of hollows and under hummocks.The high carbon and oxygen exposure environment in hummocks were the important reasons for its high CH4 production and oxidation potential respectively.(4)CH4 transport was spatiotemporal and heterogeneous in the microgeomorphologic pattern.Spatially,the soluble CH4 concentration of soil pore water appears in hollows was higher than under hummocks and hummocks.There was a significant time variability in the transmission rate of CH4 between the sedge and hummocks.The CH4 transmission variation coefficients of sedge and hummocks at different sampling times were 452.08%and-241.76%,respectively.Segde had a strong gas transmission function,which can release the CH4produced by the soil into the atmosphere and avoid oxidation by the aerobic soil layer.Hummocks had a strong ability to transport oxygen,and the existence of the vascular system can effectively oxidize CH4,which has an important regulatory effect on the carbon output of the wetland.(5)In the Carex schmidtii peatlands,CH4 emission flux had temporal and spatial heterogeneity.The emission flux of soil CH4 showed a single-peak curve trend with time.Spatially,the average CH4 emission flux in hollows was significantly higher than in hummocks(p<0.05),which were(426.94±153.52)and(172.02±81.59)mg·m-2h-1,respectively.WL,ST,soil water content(SWC),SOC and soil nutrient(TN,TP)were the main factors affecting the spatiotemporal variation of CH4.Among them,WL and ST were the main factors affecting the seasonal dynamics of CH4 emission.WL affects the decomposition of organic matter and CH4 emission in wetland by affecting soil moisture,temperature and aerobic-anaerobic respiration of soil microorganisms.However,ST controlled the seasonal variation of CH4 emission by influencing microbial activity and vegetation growth.The main factors affecting the spatial dynamics of soil CH4 emission were WL,SWC,SOC and soil nutrients.WL causes spatial heterogeneity of soil CH4 emissions by affecting the REDOX environment of soil,while SWC,SOC and soil nutrients affect spatial dynamics of CH4emissions by affecting the activity and distribution of soil microorganisms and the production of root exudates.(6)There were obvious temporal and spatial differences in the cumulative carbon emission of CH4 from the soil between the hummocks and the hollows in the growing season.The cumulative emission of CH4-C from the soil in 2019 was significantly lower than 2020,and the cumulative emission of CH4-C in the two years in hollows was significantly higher than hummocks.Combining the distribution density of hummocks and two years of field monitoring data,the average cumulative emission of soil CH4-C in the growing season was(1.05±0.04)×103g/m2.The raised hummocks in the Carex schmidtii peatlands have caused the heterogeneity of the wetland environment on a small scale,and have a significant impact on the production,oxidation,emission and transmission of soil CH4.The oxidation of CH4 in hummocks plays a leading role in the release of CH4,which can effectively reduce CH4 emissions,and has an important regulatory effect on carbon output from wetlands.Therefore,this study will help understand Carex schmidtii peatlands CH4 release process and the influence mechanism,effective support peatlands CH4 emissions and coupling relationship between environmental and biological factors,but also to accurately assess Carex schmidtii peatlands CH4 emissions.It is of great significance for the quantitative assessment and accurate estimation of CH4emissions from peatlands in the context of global climate change. |
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