The Characteristic Of Soil Activated Carbon And Nitrogen And Greenhouse Gas Fluxes Of The Different Types Of Forests In Shennongjia

The carbon cycles are important components of global carbon cycles,and plays an irreplaceable role in global carbon balance.Minor changes in forest soil may influence atmospheric CO2 concentrations,and then exert a great impact on the distribution,composition,structure and function of terrestrial ecosystem.Shennongjia is located in Qin-Ba Mountain Areas,and situated in the catchment area of the two major water conservancy projects in China(Three Gorges Project and middle route of South-to-North Water Transfer Project),the stability of the forest ecosystem is closely related with the ecological security of our country,and is the vital lifeblood of the country's economic development.Long-term human activity,especially after human interference,Shennongjia region has formed large areas of secondary forest and artificial forest.The investigation of the variation in soil active carbon and nitrogen as well as greenhouse gas flux after the change of forest types,and the simulation of soil greenhouse gas fluxes of different forest types under the background of precipitation change and related influencing mechanism,have important scientific meanings in sustainable management of local forest and forecasting the feedback effects between global warming and terrestrial ecosystem.This study took mixed evergreen and deciduous broadleaved forest(MF)and Betula luminifera secondary forest(BF),Pinus massoniana artificial forest(PF)in northern tropical Shennongjia as study objects.The design of the complete random zone experiment was adopted.We investigated the soil activated carbon and nitrogen concentrations of the three forest types,studied the variation characteristics of soil activated carbon and nitrogen content and greenhouse gases fluxes by positioning observation method,and analyzed the dynamics of soil activated carbon and nitrogen concentrations as well as greenhouse gases fluxes,and explored the responses of soil greenhouse gases to precipitation change and related influencing mechanism.The main results were as follows:1.There were great variations in the tree species composition in the three forest types.The dominant species of MF were Cyclobalanopsis oxyodon,Cyclobalanopsis multinervis and Fagus engleriana,evergreen and deciduous species accounted for 58.29%and 41.71%,respectively;the dominant species of BF were Betula luminifera,Carpinus hupeana,Platycarya strobilacea and Castanea henryi,the dominant species were deciduous species and accounted 92.31%;the dominant species of PF was Pinus massoniana,evergreen and deciduous species accounted for 21.45%and 78.55%,respectively.The DBH patterns of the three forests presented as typical anti "J" model,tree height mainly distributed in 4-9 m.2.Soil activated carbon and nitrogen concentrations changed significantly after the change of forest types.After changing from MF to BF and PF,DOC,DON,NH4+-N,NO3--N,MBC and MBN reduced significantly.The DOC and MBC of the three forest types were higher in spring,summer and winter,and lower in autumn.DON was higher in spring and summer,and lower in autumn and winter.There was no significantly difference in NH4+-N,NO3--N and MBN concentrations among different seasons.3.There were significant variation characteristics in soil greenhouse gas fluxes in the three forest types.MF,BF and PF were the sink of CH4,the source of CO2 and N2O.The CH4 and N2O fluxes ranked as MF>BF>PF,CO2 fluxes ranked as PF>BF>MF.The CH4 and CO2 fluxes of the three forest types in summer and autumn were higher than those in spring and winter.There was no significant variation in N2O fluxes dynamic changes.4.Changed precipitation greatly altered forest soil greenhouse gas fluxes.After precipitation decreased by 25%,increased the CH4 fluxes of BF by 58.12%,and reduced that of MF and PF by 53.07%and 16.08%,respectively.The CO2 fluxes of MF increased by 5.12%,CO2 fluxes of BF and PF reduced by 5.48%and 19.33%,respectively.The N2O fluxes of MF increased by 38.46%,N2O fluxes of BF and PF reduced by 41.46%and 31.03%,respectively.In the treatment of 50%reduction of precipitation,the CO2 fluxes of MF,BF and PF reduced by 15.72%,6.39%and 28.30%,respectively.The CO2 fluxes of MF increased by 3.92%,while that of BF and PF reduced by 8.04%and 22.14%,respectively,the N2O fluxes of MF and PF increased by 71.15%and 11.21%,respectively.The N2O fluxes of BF reduced by 46.34%.5.Changed precipitation altered the temperature sensibility of forest soil greenhouse gas fluxes.The temperature sensibility of the soil greenhouse gas fluxes ranked as BF>MF>PF;After the precipitation were reduced by 25%and 50%,the temperature sensibility of the soil greenhouse gas fluxes ranked as BF>PF>MF.There into,after precipitation was reduced by 25%,the temperature sensibility of MF was reduced by 21.21%,BF and PF were enhanced by 7.26%and 28.02%,respectively.After precipitation was reduced by 50%,the temperature sensibility of MF and BF were reduced by 5.72%and 38.63%,respectively,while PF was enhanced by 25.86%.6.Soil temperature and soil moisture were the main environmental factors influencing soil CH4 and N2O fluxes of the three forest types,soil temperature was the main environmental factor influencing soil CO2 fluxes.After the reduction of precipitation,soil temperature and soil moisture were the main environmental factors influencing soil CH4 fluxes and MF soil CO2 fluxes,soil moisture was the main environmental factors influencing BF and PF soil CO2 fluxes,the soil N2O fluxes of the three forest types were inapparent dependent on temperature and moisture.