Characteristic Of Soil Carbon And Nitrogen Contents And Enzyme Activities In Permafrost Regions Of Daxing’an Mountains

With the global warming,the permafrost regions gradually degenerate and shrink,and the carbon stored in the permafrost slowly releases to the atmosphere,thus affecting the regional carbon and nitrogen cycle.China is the third largest permafrost country in the world,with about 22% of its area covered by different types of permafrost.As an important forestry base in China,the Daxing’an Mountains distributed typical permafrost in high latitude.Under the background of climate warming,the process of soil carbon and nitrogen cycle is bound to change.Therefore,we selected the typical forest(Larix gmelinii,Pinus sylvestris var.Mongolica,Betula platyphylla)in permafrost regions of Daxing’an Mountains as the research objects,analyzing the change regularity of soil carbon and nitrogen contents and soil enzyme activities of different forest types during the growing season(from May to September),and discussed the environmental factors affecting soil carbon and nitrogen contents and soil enzyme activities.Revealing the changes of soil carbon and nitrogen pools in permafrost regions under the background of climate warming,which provides an important theoretical basis for studying the biogeochemical cycle process of permafrost.The main research results are as follows:(1)The soil carbon and nitrogen contents and soil enzyme activities of Larix gmelinii,Pinus sylvestris var.mongolica and Betula platyphylla all showed obvious seasonal dynamic changes,and the change trend of surface soil(0-10cm)was basically the same as that of underlying soil(10-20cm).The soil organic carbon,dissolved organic carbon and total nitrogen contents of the three forest types all showed a "double peak" pattern,which peaked in June and August respectively.The content of ammonium nitrogen and nitrate nitrogen in forest soils tended to increase,decrease and increase.The activities of urease,invertase and cellulase in Larix gmelinii and Pinus sylvestris were higher in summer,lower in spring and autumn,and the change range was larger.The activities of urease and invertase in Betula platyphylla soil were higher in summer,while the activities of cellulase in autumn were higher than those in spring and summer.(2)There were significant differences in soil carbon and nitrogen contents and soilenzyme activities of different forest types throughout the study period(from May to September).There were significant differences in soil organic carbon between Pinus sylvestris var.mongolica and Betula platyphylla and dissolved organic carbon between Pinus sylvestris var.mongolica and Larix gmelinii in 0-10 cm layer(P<0.05).The total nitrogen content of Larix gmelinii soil was significantly different from that of Betula platyphylla soil(P<0.05).There were significant differences in soil ammonium nitrogen content and invertase activity between Larix gmelinii,Pinus sylvestris var.mongolica and Betula platyphylla(P<0.05).The urease activity of Larix gmelinii soil was significantly different from that of Pinus sylvestris var.mongolica and Betula platyphylla(P<0.01).In the 10-20 cm layer,the organic carbon,ammonium nitrogen content and urease activity of Betula platyphylla were significantly higher than those of Pinus sylvestris var.mongolica(P<0.05).The soil total nitrogen content and urease activity of Betula platyphylla were respectively significantly higher and extremely significantly higher than those of Larix gmelinii.(3)In the vertical direction,the contents of soil organic carbon,dissolved organic carbon,total nitrogen,ammonium nitrogen,nitrate nitrogen and soil urease,invertase and cellulase activities of the three forest types decreased with the depth of the soil profile.(4)The correlation analysis showed that the contents of soil organic carbon,ammonium nitrogen,nitrate nitrogen and invertase activity were positively correlated with water content(P<0.01),and the contents of soil organic carbon,ammonium nitrogen,urease and invertase activities were negatively correlated with pH value(P <0.01).Soil organic carbon content was significantly positively correlated with total phosphorus and available phosphorus content(P<0.05).Soil cellulase activity and dissolved organic carbon content were significantly positively correlated with total phosphorus(P<0.05)and extremely significantly positively correlated with total phosphorus(P<0.01).The contents of soil organic carbon and ammonium nitrogen had significant effects on soil urease and invertase activities(P<0.01).The contents of soil organic carbon and dissolved organic carbon had great influence on soil cellulase activity(P<0.05).