| Nitrous oxide(N2O)is an important greenhouse gas playing an important role in both global climate change and stratospheric ozone depletion.The riparian marsh plays an important role in modulating atmospheric concentrations of N2O.The static chamber-GC techniques were used to explore the spatiotemporal variations of N2O fluxes in Calamagrostis angustifolia swamp meadow marsh(CASMM),Ecotone wetland(EW)and Carex Schmidtii Meinsh.marsh(CSMM)along the pristine riparian in Sanjiang Plain from October 2015 to October 2016.During the non-growing season(October 2015 to April 2016),growing season(May 2016 to October 2016),Freeze-Thaw Cycles(FTCs,March to April,2016)and the whole year(October 2015 to October 2016),the source/sink and the spatiotemporal variations of N2O flux and its influencing factors were investigated systematically for CASMM,EW and CSMM in Sanjiang Plain.The main research results show that:(1)Explaining the variations of N2O fluxes in the riparian marshes in different periods.During the non-growing season,all the three marshes were found to absorb N2O over all sampling times from the end of October 2015 to March 2016.However,N2O emission fluxes were mainly observed in the middle of October 2015 and from March to April 2016.The maximum emission peak and maximum absorption peak were observed in autumn and winter respectively,which all occurred in CASMM.During the non-growing season,the N2O average fluxes in the three marshes showed CASMM(-18.58 ?g m-2 h-1)>EW(-10.39 ?g m-2 h-1)>CSMM(-2.72 ?g m-2 h-1).Statistical analysis showed significant differences(P<0.001,n=33,2000 iterations)in the variability of N2O fluxes among the three marshes during the non-growing season.During the growing season,N2O fluxes in the three marshes showed CASMM(17.32 ?g m-2 h-1)>EW(15.47?g m2 h-1)>CSMM(-8.03 ?g m2 h-1);The variabilities of N2O fluxes in the three marshes were significantly different(P<0.001,n=33,2000 iterations).The maximum emission peak and maximum absorption peak during the growing season were all observed in autumn of 2016,which occurred in CASMM and CSMM,respectively.During FTCs,the average flux of N20 in the three marshes in the riparian wetlands showed CSMM(27.35±27.44 ?g m-2 h-1)>EW(23.36±27.94 ?gm-2 h-1)>CASMM(11.67 ± 47.81 ?g m-2 h-1);Both the maximum emission peak and maximum absorption peak of the three marshes were observed in March and April in CASMM.N2O fluxes in the three marshes were significantly different(P<0.001,n=15,10000 iterations)during FTCs.During the whole year,the average annual flux of N2O in the three riparian marshes showed that CSMM(-5.60±11.30?g m-2 h-1)>EW(2.39±18.57 ?g m-2 h-1)>CASMM(-0.88±11.26 ?g m-2 h-1),but the N2O fluxes of the three riparian marshes were not significantly different(P>0.05,P=0.858,n=22).(2)Exploring the influencing factors of N2O fluxes in the riparian marshes in different periods.During non-growing season,the influencing factors of N2O fluxes in CASMM,EW and CSMM were air temperature and soil NH4+-N content in the a to 10 cm soil depth;air temperature;and air temperature and soil volumetric moisture content in the 10 to 20 cm soil depth,respectively.During growing season,the influencing factors of N2O fluxes in CASMM were soil NH4+-N content in the 30 to 40 cm soil depth,the influencing factors of N2O fluxes in EW was affected by the interactions of multiple environmental variables,and the influencing factors of N2O fluxes in CSMM was soil NH4+-N content in the 20 to 30 cm soil depth and soil NO3--N content in 0 to 10 cm soil depth.During FTCs,soil NH4+-N and soil NO3--N content were the main influencing factors of N2O fluxes in CASMM.However,the influencing factors of N2O fluxes during FTCs in EW and CSMM were uncertain.Further studies will be required to understand the influencing factors of N2O fluxes in EW and CSMM during FTCs.During the whole year,atmospheric temperature and NH4-N content in the soil depth of 30 to 40 cm were the key influencing factors of N2O fluxes variations in CASMM,and atmospheric temperature was the key influencing factor of N2O fluxes variations in EW.However,the variations of N2O flux in CSMM may be affected by the interactions of multiple environmental factors.(3)Revealing the source or sink of N2O fluxes in the riparian marshes in different periods.During the non-growing season,the three pristine riparian marshes became sinks of N2O;However,during the growing season,the whole pristine riparian marsh became a source of N2O.During the non-growing season,CASMM and EW were the sinks of N2O.But they became the sources of N2O during the growing season.However,CSMM was a sink of N2O during every season.The results showed that the three marshes were all the potential sources of N2O during FTCs.The results indicated that the three riparian marshes acting as a N2O sink in the whole year and winter.However,they became the source of N2O in spring,summer and autumn.However,CASMM and CSMM were all the sinks of N2O,EW was a source of N2O during the whole year.But,the changes of source and sink of N2O fluxes in the three riparian marshes with seasonal changes.(4)In the three marshes,the contribution rates of N2O emission flux in CASMM,EW and CSMM in the non-growing season to the annual N2O emission flux are respectively 43.33%,41.27%and 77.22%.CASMM,EW and CSMM respectively contributes 56.67%,58.73%and 22.78%of the annual N2O emission flux in the growing season.In addition,the contribution rates of N2O emission flux in CASMM,EW and CSMM during freezing-thawing cycle reached 28.47%,29.42%and 62.46%respectively in the whole year.This study relied on China's largest freshwater marsh wetland-Sanjiang Plain riparian marsh wetland,and systematically revealed the spatiotemporal variations and a source or sink of N2O flux in the riparian marsh of Sanjiang Plain during the non-growing season,growing season,soil freezing and thawing cycle and the whole year.The influencing factors of N2O fluxes in different types of riparian marshes in different periods were determined.This study laid the foundation for the study of N2O fluxes in the riparian marsh of the Sanjiang Plain,and can provide scientific basis for the development and protection of wetlands. |
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