The Effect Of Paddy Field Management Change On Ecosystem CO₂ Emission And Carbon Budget

In recent years,how to reduce the emissions of greenhouse gases?especially CO₂?has become a major challenge for governments.Human activities interfere with the carbon cycle and increase the concentration of CO₂ in the atmosphere mainly through the burning of fossil fuels and the way of land use change.The change of surface cover by different land use patterns not only changes the net primary productivity of the surface,but also directly affects the ecological system of the absorption of CO₂ in the atmosphere,thus affecting the source/sink function of the ecosystem.Paddy cultivation and dry land cultivation as two common farmland planting patterns,the different of the physical and chemical environment and management measures will undoubtedly lead to huge difference in carbon cycle.In this study,CO₂ emissions changes by converting paddy land use as the breakthrough point,conversion of winter paddy fields to rice-wheat rotation or double-cropping paddy fields to vegetable land,paddy field from flooded environment to rice field-upland field rotation or dryland rotation.By the static opaque chamber and gas chromatography techniques,CO₂ fluxes were analyzed to explore the CO₂ emission characteristics of ecosystem after conversion in paddy field.The CO₂-C income and expenditure of the system were estimated to determine the rotation of winter paddy fields to rice-wheat rotation or double-cropping paddy fields to vegetable land whether can fixed more carbon,to provide effective mitigation measures for carbon emissions from paddy ecosystems,and provide a reference for assessing the impact of land use change on agro-ecosystem carbon cycling.In this study,we selected 6 piece of winter flooded paddy field in Yanting County,Sichuan Province and 6 piece of double-cropping paddy field in Changsha County,Hunan Province as the research object.Among them,three winter paddy fields?RF?were converted to rice-wheat rotation?RW?,and three double-cropping paddy fields?DR?were converted to vegetable land?PV?.winter paddy field,rice-wheat rotation,double-cropping paddy field and vegetable land should be set up two sub-processing,respectively,including plant conventional fertilization?UN?and non-planted conventional fertilization area?BL?.Field management and fertilization take the local regular management model.CO₂ flux,biomass and ammonium nitrogen?NH4+-N?,nitrate nitrogen?NO3--N?and dissolved organic carbon?DOC?of soil were measured,respectively.The main research findings are as follows:?1?The CO₂ emission from altering winter paddy field to rice-wheat rotation showed the general rule of "high in rice season and low in wheat season",while the cumulative flux of each treatment was RW-UN>RF-UN>RW-BL>RF-BL,and the cumulative annual emissions in 2014 are lower than the corresponding value for 2013.CO₂ emissions from altering double-cropping paddy field to vegetable land was obviously different,the cumulative emissions of each treatment in 2013 was DR-UN> PV-UN> PV-BL> DR-BL,while in 2014 and 2015,the cumulative emissions were PV-UN> DR-UN.?2?After altering winter paddy field to rice and wheat crop rotation,the net annual emissions of rice and wheat rotation was-7.32 t C ha-1,which was lower than the net annual emissions-4.15 t C ha-1 of the winter paddy field,indicating a significantly increase in carbon sequestration in the system after conversion.In three consecutive years,the mean annual net emissions of vegetable land and double cropping paddy field were-5.26 t C ha-1 and-4.73 t C ha-1,respectively,although there was no significant difference between the two treatments,but the carbon sequestration was higher than that of double cropping paddy fields,indicating that the conversion can fix more carbon dioxide.From the perspective of ecosystem CO₂-C,the conversion of rice land use is beneficial to the environment.?3?Changing planting patterns and crop species can change the farmland ecosystem carbon source and carbon sequestration of carbon cycle form,to a certain extent.The net ecosystem exchange of CO₂ in farmland ecosystem is affected by soil anoxic respiration,but it is consistent with the change of NPP value.When the NPP value is large,the amount of fixed carbon dioxide is also large,more performance as a carbon sink;when the NPP value is small,the amount of fixed carbon dioxide is also small,as carbon sources.Conversion of winter paddy fields and double cropping paddy field land use,increase the multiple cropping index,choose the biomass crop,can fix more carbon and reduce the farmland ecosystem CO₂ emissions.?4?After altering winter paddy field to rice and wheat crop rotation,the influence on rice production was not significant,but increase the wheat output of one season,is beneficial to farmers.However,the yield of early rice and late rice was not significantly during three consecutive years,and early rice yield is far lower than the late rice,more farmers abandoned the early rice cultivation and chose only one season of mid-season rice so that the leisure period was longer,so to make the rice field show stronger carbon source,conversion of paddy fields use is conducive to ease the carbon source emissions.?5?Converting paddy fields use way to make soil soluble carbon and nitrogen content,moisture,temperature changes,result in significant different in CO₂ fluxes and changes in farmland ecosystems,indicating that soil carbon and nitrogen,moisture,temperature can affect CO₂ emissions,especially when the change of water conditions from paddy field to dryland has a great impact on CO₂ emissions.