Research On Soil Greenhouse Gas Emissions And Its Influencing Factors Of Returning Farmland To Wetland

Since the 20th century,agricultural reclamation had led to the conversion of a large number of wetlands into farmlands,which led to more greenhouse gas emissions.It exacerbated the potential risks of global warming and had an uncertain impact on the global climate.In recent years,a series of impacts caused by wetland atrophy and functional degradation have attracted widespread attention.In wetland areas that have been severely damaged by agricultural reclamation,the policy of returning farmland to wetland had gradually been implemented.At present,researches on wetland soil greenhouse gas emissions focus on natural wetlands,artificial wetlands and degraded wetlands,but less on the land of returning farmland to wetland.In the process of returning farmland to wetland,various factors will have an uncertain impact on soil greenhouse gas emissions.Therefore,it is of great significance to clarify the characteristics of soil greenhouse gas emission and its influencing factors during the process of returning farmland to wetland.It provides a reference for evaluating the restoration effect of returning farmland to wetland,and provides a scientific basis for the subsequent work of returning farmland to wetland.It is of great significance for predicting future local and global climate change.In this study,the returning farmland to wetland(years of returning farmland to wetland:2010,2014,2016),farmland,and natural wetland soils in the Honghe National Nature Reserve in the Sanjiang Plain were used as research objects.The soil greenhouse gas emissions were the core of the research.Through indoor simulation experiments,using closed-air chamber-gas chromatography method to determine the soil greenhouse gas emissions.The soil greenhouse gas CO₂,CH₄,and N₂O emissions characteristics under different water levels,different water level fluctuation scenarios,litter addition,and nitrogen deposition were studied.We explored and evaluate the impact of the above factors on soil greenhouse gas emissions and their changes during the process of returning farmland to wetland.The main conclusions are as follows:(1)When the water level was constant at-5cm,0cm and 5cm,the water level had a significant impact on soil greenhouse gas emissions of returning farmland to wetland and natural wetland.The CO₂ and N₂O emission fluxes decreased as the water level rose.The CH₄ emission fluxes were highest when the water level was 0cm.The duration of the experiment had no significant effect on the CO₂and N₂O emission fluxes,but significantly increased the CH₄ emission fluxes.(2)When the water level fluctuated between-8 and 8cm,water level fluctuation had a significant impact on the soil greenhouse gas emissions of returning farmland to wetland and natural wetland.As the average water level increased,the CO₂ and N₂O emission fluxes rose.CH₄ emissions were highest in treatment V(alternating scenarios during water level fluctuations).Anaerobic/aerobic environment and ventilation conditions were factors that collectively affected greenhouse gas emissions during water level fluctuation.CO₂ was the most important factor affecting the global warming potential in this experiment.(3)With the increase of the years of returning farmland to wetland,the CH₄emission fluxes showed an increasing trend.And inhibition of submergence on global warming potential was also more significant.Therefore,in the process of returning farmland to wetland,reasonable elevation of water levels and reduction of greenhouse gas emissions could be taken as a short-term strategy.When the surface soil was not significantly submerged,appropriate water level fluctuations could also effectively restrain the global warming potential.(4)The addition of litter promoted soil CO₂ emissions from returning farmland to wetland and natural wetland but had no significant effect on CH₄ emissions.The addition of litter had an inhibitory effect on natural wetland soil N₂O emissions.For the land of returning farmland to wetland,adding litter of returning farmland to wetland increased soil N₂O emissions slightly.The addition of litter significantly increased the global warming potential of soil greenhouse gas emissions,which was mainly due to the significant increase in soil CO₂ emissions by the addition of litter.In the process of returning farmland to wetland,attention should be paid to the differences in the effects of different types of litter and their different decomposition levels on soil greenhouse gas emissions.(5)Nitrogen deposition significantly increased soil N₂O emissions.Soil N₂O emissions fluxes from returning farmland to wetland and natural wetland had a downward trend.Nitrogen deposition significantly increased farmland soil CO₂emissions.N10 treatment significantly increased soil CO₂ emissions from returning farmland to wetland.But nitrogen deposition had no significant effect on natural wetland soil CO₂ emissions.Nitrogen deposition significantly inhibited soil CH₄emissions of farmland and natural wetland,especially in natural wetlands.Nitrogen deposition had no significant effect on soil CH₄ emissions from returning farmland to wetland.During the process of returning farmland to wetland,nitrogen deposition exacerbates the risk of soil greenhouse gas emissions to global warming,which is mainly due to the stimulating effect of nitrogen deposition on N₂O emissions.And the risks brought about by it cannot be ignored.