Analysis On Characteristics And Influencing Factors Of Greenhouse Gas Emission From Flooded Soil In Wetlands Under Freeze-thaw Disturbance

Under the background of global climate change,the phenomenon of soil freeze-thaw alternation is becoming more extensive and common.The change of freeze-thaw pattern will have a profound impact on soil physico-chemical properties and biological characteristics,which will in turn change the rules of soil greenhouse gas emissions.The wetland is a unique ecosystem formed by the interaction of water and land,functioning as a huge carbon and nitrogen source and sink.Wetland water level has been fluctuating for a long time,but the mechanism of freezing and thawing on greenhouse gas emissions from water-covered wetland is still not clear.Our paper investigated the emission rules of carbon dioxide（CO₂）,methane（CH₄）and nitrous oxide（N₂O）from flooded Phragmites australis communities and plant-free zones,and discussed the effects of the three greenhouse gas emissions from the perspective of soil environmental factors,microbial community structure and enzyme activity.The main conclusions are as follows:（1）Freezing and thawing increased the CO₂emission rate of wetland soil,and the rate of increase in plant-free zone was higher than in P.australis communities soil;under freez-thaw treatments,flooding reduced the average rate of CO₂emission,and the rate in P.australis communities soil decreased by 6.32%compared to the plant-free zone.Soil water content（SWC）,total phospholipid fatty acid（TPLFA）,peroxidase（PER）and polyphenol oxidase（PPO）are the common influencing factors of soil CO₂emission in the two wetlands under freeze-thaw treatments.Dissolved organic carbon（DOC）,β-N-acetyl-glucosaminidase（NAG）,total nitrogen（TN）and soil organic matter（SOM）are factors that affect soil CO₂emissions from P.australis communities soil.Nitrate nitrogen（NO₃^––N）andβ-glucosidase（BG）are factors that affect soil CO₂emissions in the plant-free zone.The CO₂emissions in two wetlands are mainly directly affected by flooding,which can effectively reduce CO₂emissions,and flooding in the plant-free zone also indirectly affects soil CO₂release by enhancing PER activity.（2）After freezing and thawing,the CH₄emission rate of the unflooded soil increased,while the flooded soil decreased;under freez-thaw treatments,the average CH₄emission rate in the flooded soil was lower than that in the unflooded soil,and the soil of P.australis communities decreased more significantly than that of the plant-free zone.SWC,NAG,PER and PPO are the common influencing factors of soil CH₄emissions in the two wetlands under freeze-thaw treatments.DOC and NO₃^––N are factors that affect CH₄emissions from P.australis communities soil.Electrical conductivity（EC）is a factor that affect CH₄emissions from plant-free zone.The CH₄emissions in two wetlands are mainly directly affected by flooding,which can significantly reduce CH₄emissions.Meanwhile,flooding can regulate enzyme activities and EC by increasing SWC to indirectly affecting CH₄emissions.（3）The N₂O emission rates in P.australis communities soil decreased and in plant-free zones increased respectively after freezing and thawing;under freeze-thaw treatments,flooding reduced the average N₂O emission rate in P.australis communities soil,but increased in plant-free zones.SWC,EC and BG are the common influencing factors of soil N₂O emission in the two wetlands under freeze-thaw treatments,NAG,DOC,p H,PER and NO₃^––N are the factors that affect the P.australis communities soil N₂O emission.PPO and SOM are the factors that affect N₂O emissions from plant-free zones.The main influencing pathways of N₂O emissions from two wetlands are different.Flooding mainly promotes N₂O emission by increasing the SWC of P.australis communities soil,but in the plant-free zones,the increase of N₂O emission is mainly directly affected by flooding.（4）The results of this study show that in the practice of managing constructed and natural wetlands with seasonal freezing and thawing,flooding measures can reduce greenhouse gas emissions.These results provide a scientific basis for further explaining the transformation mechanism of source and sink functions of wetland ecosystems,predicting its potential contribution to future climate warming,as well as providing guidance information for comprehensive assessment of wetland functions and scientific management of constructed wetlands.