| The increasing concentrations of atmospheric CO2 and CH4 emission are the main cause of globle warming.It is necessary to further study the spatiotemporal variability of small-scale CO2 and CH4 emissions in order to quantify the CO2 and CH4 emissions from wetland ecosystems on a regional scale.As one of the most important organic carbon pools in terrestrial ecosystems,peatands play an important role in maintaining global carbon source/sink relationships and climate change.Carex peatlands are widely developed in high latitude regions of northern hemisphere,and the microtopography may have a significant impact on the temporal and spatial dynamics of soil CO2and CH4 emissions.Therefore,this study investigated the emission fluxes of soil CO2 and CH4 in diffirent microtopography part?hummocks and hollows?and diffirent water level conditions?high and low water level?,combined with soil temperature?ST?,water level?WL?,soil organic carbon?SOC?,total nitrogen?TN?,total phosphorus?TP?and soil?-glucosidase??G?,N-acetylglucosaminidase?NAG?,acid phosphatase?AP?,and peroxidase?PER?in the growing season in a Carex schmidtii peatland of Changbai Mountain,Northeast of China.This study expounded the temporal and spatial dynamics of soil CO2 and CH4 emissions,evaluated the cumulative emissions of soilCO2 and CH4 during the growing season of the Carex peatland and clarified the soil CO2 and CH4 emissions characteristics in hummock-microtopography.On this basis,the effect and rate of contribution of non-biological factors?ST,WL,pH,SWC,SOC,TN and TP?and biological factors?soil?G,NAG,AP and PER enzymes?on soil CO2 and CH4 emmision were analyzed to reveal the influencing mechanism of hummock-microtopography on soil CO2 and CH4emissions in the Carex peatland.The main conclusions were following:?1?Environmental factors showed significant spatial heterogeneity in the Carex peatland.Variance analysis showed that the soil temperature?ST?,soil pH and soil organic carbon?SOC?content in hummocks were significantly higher than those in hollows?p<0.05?,but soil total nitrogen?TN?and total phosphorus?TP?contents were significantly lower than those in hollows?p<0.05?.The water level?WT?in hummocks was lower than that in hollows,but WL was not significant difference between hommocks and hollows?p>0.05?.The SWC content in soil 0-10cm layer in hummocks was significantly lower than that in hollows?p<0.05?,while the SWC content in soil10-20cm layer in hummocks was significantly higher than that in hollows?p<0.05?.Among the biological factors,the activities of soil hydrolase??G,NAG and AP enzymes?were significantly higher in hommocks than that in hollows?p<0.05?,while the activity of PER enzyme was significantly lower than that in hollows?p<0.05?.?2?In the Carex peatland,the soil CO2 and CH4 emission fluxes had obvious seasonal dynamics in hummocks and hollows.The soil CO2 emission flux of hummocks and hollows all showed that low-value areas of emission flux were in spring or autumn,and peak areas of emission flux appeared in summer.Among them,the minimum value of soil CO2 emission flux in hummocks was279.52±46.77 mg m-2 h-1,which appeared in October,and the maximum value was 2021.03±34.40mg m-2 h-1,which appeared in July.The minimum soil CO2 emission flux in hollows was 68.76±0.44mg m-2 h-1,which appeared in May,and the maximum value was 735.26±166.93 mg m-2 h-1,which appeared in August.The soil CH4 emission flux showed obvious unimodal change trend in the growing season in hummocks and hollows.The low flux area of soil CH4 emission flux of hummocks and hollows all appeared in the spring and the peak area all appeared in the summer.Among them,the minimum value of soil CH4 emission flux in hummocks was 1.29±0.07 mg m-2 h-1,which appeared in May,and the maximum value was 502.44±30.14 mg m-2 h-1,which appeared in August.The minimum soil CH4 emission flux in hollows was 0.64±0.21 mg m-2 h-1,which appeared in May,and the maximum value was 500.13±35.89 mg m-2 h-1,which appeared in July.?3?In the Carex peatland,the average emission flux and the cumulative emission flux of soil CO2 and CH4 all showed spatial heterogeneity during the growing season.The average emission flux of soil CO2 in the growing season showed hommocks in low water level>hommocks in high water level>hollows in high water level>hollows in low water level,and the average emission flux of soil CO2 was significantly different between hummocks and hollows?p<0.05?.The average emission flux of soil CH4 in the growing season showed hollows in high water level>hollows in low water level>hummocks in high water level>hummocks in low water level or hollows in high water level>hollows in low water level>hummocks in low water level>hummocks in high water level.The cumulative emission of soil CO2-C in the growing season was as following:hommocks(1.03×106 mg/m-2)>hollows(0.28×106 mg/m-2),while the cumulative emission of soil CH4-C in the growing season was hummocks(3.45×105 mg/m-2)>hollows(2.30×105 mg/m-2).Combined with the distribution density of hommocks,the cumulative CO2-C was 0.51×106 mg/m-2,and the cumulative emission of soil CH4-C was 3.12×105 mg/m-2 in the growing season in the Carex peatland.That was,there was significant spatial heterogeneity in the cumulative emissions of soil CO2-C and CH4-C and the cumulative carbon emission per unit area was 8.22×105 mg during the growing season of the Carex peatland.?4?Correlation analysis showed that ST,WL,pH,SOC,TP,?G enzyme,AP enzyme and PER enzyme were significantly correlated with the soil CO2 emission in the hummocks?p<0.05?,and linear regression analysis and path analysis showed that the main factors affecting the seasonal variation of soil CO2 emission flux were SOC,WL,pH,ST,PER and?G enzymes in hummocks,and their contribution rates were 21.31%,18.01%,17.09%,16.03%,11.19%and 11.01%,respectively.Among them,soil enzymes mainly affect the seasonal changes of soil CO2 emissions by affecting SOC.The ST and NAG enzymes were significantly correlated with the soil CO2 emission flux in hollows?p<0.05?,and were the main influencing factors for the seasonal variation of CO2 emission flux in hollows,with contribution rates of 61.73%and 38.27%,respectively.The environmental factors related to the soil CH4 emission flux were WL,SOC,TN,TP and PER enzymes in hummocks and linear regression analysis and path analysis showed that the main factors affecting the seasonal variation of soil CH4 emission flux were pH,TN,TP and PER enzyme,and their contribution rates were 31.01%,25.68%,25.41%,and 11.35%,respectively.WL hads a high indirect effect on the seasonal variation of soil CH4 emissions by affecting soil nutrients?TN and TP?in hummocks.The environmental factors related to the soil CH4 emission flux were WL,ST,pH and NAG enzymes and linear regression analysis showed that the main reasons for the seasonal variation of soil CH4emission fluxes were ST,pH and WL and their contribution rates were 44.97%,27.52%and 24.20%,respectively,mainly through direct effects on the seasonal variation of CH4 emission flux in hollows.?5?Linear regression analysis and path analysis showed that the important impact factors of soil CO2 emission had SOC,PER enzyme,TP,pH,?G enzyme and ST,and their contribution rates were33.44%,24.43%,20.47%,7.75%,4.63%,and 4.59%,respectively.Among them,SOC,TP and soil PER activities were mainly direct impact factors,while microclimate?ST?and other physical and chemical properties?pH,SWC?were indirectly affected to soil CO2 emission by soil nutrient?SOC,TP?and soil?PER?enzyme activities.The factors affecting soil CH4 emission flux were soil?G enzyme,ST,WL,pH,NAG enzyme and SOC in hummock-microtogrophy,and their contribution rates were 30.61%,21.91%,17.22%,14.15%,11.08%and 5.03%,respectively.Among them,?G enzyme,ST,WL and pH were mainly direct influence factors,while SOC mainly affected the spatial variation of CH4 emission through affecting soil enzyme activity.The hummock-microtopography is widely distributed in peatands,and its small-scale environmental heterogeneity has a significant impact on soil carbon emissions?CO2 and CH4?in ecosystems.Therefore,this study is of great significance for quantitative assessment and accurate estimation of total soil CO2 and CH4 emissions from peatands in the context of global change,and can provide basic data for the implementation of relevant international conventions and the construction of related models in China.At the same time,it can provides data support for the ecological restoration of degraded peatands. |
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