Characteristics Of Soil Carbon And Nitrogen Content And Enzyme Activity In Marsh Wetlands In The Northern Da Hinggan Mountains

Wetlands have unique hydrological characteristics and rich biodiversity,and play an im-portant role in regulating runoff,improving water quality,and regulating microclimate.There-fore,wetlands are also known as’biological supermarkets’and’kidney of the earth’.The area of Da Hinggan Mountains wetland is 153.08×10⁴ hm²,accounting for 3.91%of the total wet-land area in China and 24.42%of the total wetland area in Heilongjiang Province.In this study,four typical swamp wetlands in the northern Da Hinggan Mountains were selected as the re-search objects,namely Alnus sibirica wetland,Sedge wetland,Larix gmelinii-Carex Schmidtii wetland and Larix gmelinii-Moss wetland.The characteristics of soil carbon,nitrogen and en-zyme activity in the 0-30 cm soil layer during the growing season were analyzed,and the changes of soil carbon and nitrogen components and enzyme activity in different swamp wet-land types in the permafrost region of the northern Da Hinggan Mountains were revealed,which provided basic data for wetland protection and nutrient cycling in permafrost regions.The main conclusions of this study are as follows:（1）From June to October,the SOC content in 0-10 cm soil layer of Alnus sibirica wetland,Sedge wetland and Larix gmelinii-Carex Schmidtii wetland increased to the maximum value of37.37 g·kg^-1,29.27 g·kg^-1 and 36.67 g·kg^-1,respectively,with an increase of 49.87%,30.46%and 89.66%,respectively.The SOC content of Larix gmelinii-Moss wetland fluctuated be-tween 20.5 and 21.93 g·kg^-1.The content of EOC in 10-20 cm soil layer of Alnus sibirica wet-land,Sedge wetland and Larix gmelinii-Moss wetland increased to the maximum in September.The fluctuation of EOC content in four swamp wetlands soils in 20-30 cm soil layer was dif-ferent.The MBC content of four kinds of swamp wetland soil was lower in June and October,and the maximum value appeared in July to September.The DOC content in the soil of four swamp wetlands varied greatly.From June to October,except for the Larix gmelinii-Moss wet-land,the DOC content of the other three marshes decreased significantly.（2）From June to October,the contents of NH₄⁺-N and NO₃^--N in the four marsh wetlands showed a fluctuating downward trend.In the surface soil,the NH₄⁺-N in the Sedge wetland decreased the most,reaching 64.47%,and the Larix gmelinii-Moss wetland decreased the least by 44.93%.Soil NO₃^--N ranged from 0.55 to 3.30 mg·kg^-1.From June to October,the content of MBN in 0-30 cm soil of Alnus sibirica wetland and Sedge wetland decreased by 25.12%and22.33%respectively,while that of Larix gmelinii-Carex Schmidtii wetland and Larix gmelinii-Moss wetland increased by 24.57%and 40.02%respectively.The content of DON was greatly affected by the type of marsh wetland.From June to October,the increase of DON content in the 0-10 cm soil layer of Alnus sibirica wetland and Larix gmelinii-Moss wetland was 77.94%and 43.86%,respectively,while that in Larix gmelinii-Carex Schmidtii wetland and Larix gmelinii-Moss wetland decreased by 23.80%and 60.42%,respectively.The change trend of DON content in the four marsh wetlands in the 10-20 cm soil layer was similar to that in the surface layer.（3）From June to October,the soil catalase activity of Alnus sibirica wetland and Sedge wetland fluctuated little,and the two kinds of Larix gmelinii swamp showed a fluctuating de-cline.The maximum decrease of 20-30 cm soil layer in Larix gmelinii-Carex Schmidtii wet-land was 55.25%,and the minimum decrease of 0-10 cm soil layer was 5.54%,and the differ-ence of 0-30 cm soil layer was significant（P<0.05）.From June to October,the sucrase activity of Larix gmelinii-Carex Schmidtii wetland and Larix gmelinii-Moss wetland was the highest in June,which was 19.38 mg·g^-1·24h^-1 and 26.10 mg·g^-1·24h^-1,respectively.The soil urease activ-ity in different soil layers of the four marsh wetlands showed a fluctuating downward trend,and the overall activity was less than sucrase.（4）The carbon and nitrogen components of Larix gmelinii-Carex Schmidtii and Larix gmelinii-Moss wetland were greatly affected by soil moisture content,and most of them were significantly positively correlated（P<0.01）.The nitrogen components of Sedge wetland and Larix gmelinii-Carex Schmidtii were greatly affected by soil p H,and most of them`were sig-nificantly negatively correlated（P<0.01）.The DOC content of the four kinds of wetland soil was greatly affected by soil temperature.The sucrase of Sedge wetland was greatly affected by soil moisture content（P<0.01）,the sucrase in Alnus sibirica wetland,Larix gmelinii-Carex Schmidtii and Larix gmelinii-Moss wetland was mainly affected by the content of carbon com-ponents（P<0.05）,and the sucrase in Sedge wetland was mainly affected by the content of EOC（P<0.05）.Soil sucrase was mainly affected by active carbon fractions（P<0.01）,while ure-ase was mainly affected by NH₄⁺-N,NO₃^--N,DON and MBN contents.Soil moisture content was significantly correlated with carbon,nitrogen and enzyme activity（P<0.05）.It can be seen that there are great differences in soil carbon and nitrogen contents and en-zyme activities among different types of marsh wetlands in the northern Great Xing’an Moun-tains,the average SOC and MBC contents in the 0-30 cm soil layer are the highest in the Alnus sibirica wetland and the lowest in the Larix gmelinii-Moss wetland.The contents of soil TN and MBN were the highest in Sedge wetland,while the two kinds of Larix gmelinii wetland were relatively low.The soil enzyme activities of different wetland types were also different,the soil catalase and sucrase activities of Sedge wetland were higher,while the urease activities of the two Larix wetland were higher.This study provides basic data for the study of soil nutri-ent cycling and mechanism in swamp wetlands in permafrost regions of China.