| The permafrost region in the Daxing'an Mountains is located in the southern margin of the Eurasian permafrost zone.Peatland is one of the main geomorphic features in permafrost region,with an area of about 3.55×10~6 km~2 in Arctic region,and2.50×10~6 km~2 in Eurasia continent.Although peat bogs account for only 3%of the land area,their soil carbon storage accounts for 15%-30%of the soil carbon pool.Soil dissolved organic carbon(DOC)is considered as the most active and sensitive indicator of peatland carbon cycle,and its accumulation and decomposition directly affect the global carbon balance.This study selected Calamagrostis angustifolia peatland(CP),Larix gmelina-sphagnum peatland(LP),and Eriophorum vaginatum peatland(EP)in the Daxing'an Mountains as the research objects,and carried out in-situ experiments to explore the variation rules of soil moisture,heat and DOC in three kinds of permafrost peatlands during autumn freezing period.The differences of soil moisture,heat and DOC in permafrost peatlands during different freezing periods were compared and analyzed to reveal the influence of soil moisture and heat changes on DOC in permafrost peatlands.The conclusions of this paper are as follows:(1)During the fall freeze period in 2019 and 2020,the DOC content of all three multi-year permafrost peatlands showed EP>CP>LP,where the mean DOC content of0-50 cm soil in 2019 was 83.99 mg-L-1,45.75 mg-L-1,and 43.13 mg-L-1,respectively.the mean DOC content of 0-30 cm soil in 2020 The mean values of soil DOC content in0-30 cm in 2020 were 110.14 mg-L-1,104.92 mg-L-1 and 63.60 mg-L-1,respectively.(2)During the fall freeze in 2019,all three perennial permafrost peatland DOC contents showed fluctuating decreasing changes in the pre-freeze period,with shallow soil DOC decreasing more than deep,and EP soil fluctuating more in the mid-freeze period,with a maximum difference of 149.76 mg-L-1.CP and EP soil DOC changed more moderately in the mid-and late-freeze periods.2020 fall freeze CP,EP shallow Soil DOC and LP shallow and deep soil DOC showed fluctuating decreasing trends from September 28 to October 7,and CP and EP deep soil DOC showed a trend of increasing and then decreasing.Overall,the DOC showed a fluctuating decreasing trend with time during the freezing period in autumn.(3)During the freezing period in autumn 2019 and 2020,the shallow soil water content was greater than the deep soil water content in all three permafrost peatlands,and the variation in the shallow soil water content was greater than that in the deep layer.the deep soil temperature was higher than the shallow soil temperature in all three permafrost peatlands,and the variation in the shallow soil temperature was greater than that in the deep soil temperature.(4)Soil temperature was the main influence on soil DOC changes during the pre-freeze and mid-freeze periods in fall 2019.In contrast,soil water content was the main factor controlling soil DOC changes during the late freeze period.Throughout the fall freeze period,LP shallow soil DOC was mainly driven by surface temperature(R~2=0.297,p<0.01),while deep soil DOC was mainly influenced by deep water content(R~2=0.196,p<0.05);overall soil DOC was more influenced by surface temperature(R~2=0.195,p<0.05).three peat species during the fall freeze period in 2020 ground soil DOC was less influenced by hydrothermal changes.(5)The soil DOC contents of CP,LP were different between the two years,and the shallow and deep soil DOC were significantly different between 2019 and 2020(p<0.05),and the EP soil DOC was significantly different between the two years only for the deep soil DOC(p<0.05).There were significant differences(p<0.05)between LP,EP 0-10 cm soil water content,and CP,LP 10-20 cm soil water content between the two years,and there were small changes in soil temperature,and only CP surface temperature had large changes. |
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