Study On CO₂ Exchange Characteristics And Influencing Factors In The Degraded Alpine Wetland

Due to the influence of climate change and human activities,the degradation of alpine swamp wetlands is getting worse,showing a degradation succession trend from wetlands to alpine meadows,which have a serious impact on the ecosystem service functions such as water conservation,species diversity and habitat of alpine swamp wetland.Many studies have confirmed the complex interactions among plant community characteristics,soil physical and chemical properties and soil carbon storage.And the degradation of alpine swamp wetlands was accompanied by significant changes in vegetation,soil physics and chemistry,and microorganisms.However,the changes of photosynthesis,respiration and their components of plant communities,their relationships with vegetation and soil environment have remained unclear.In this study,different degradation stages of alpine swamp wetlands(non-degradation,light degradation and severe degradation)were taken as objects,the basic properties of plants and soil and the characteristics of soil microbial communities in different degradation stages were studied.Furthermore,the community CO₂ exchange during the peak period of vegetation growth(July-August)was measured by TARGAS-1 static box method,and the response law of community CO₂ exchange to the succession of swamp wetland degradation was analyzed.The feasibility of root removal method and glyphosate spraying method for measuring respiration components were discussed,and the respiration components of ecosystem were detailed.And the differences in ecosystem respiration and its components were discussed,and the influencing factors on vegetation photosynthesis and ecosystem respiration were exhibited,so as to provide data support and theoretical basis for carbon exchange of alpine swamp wetland ecosystem under the background of environmental change.The main results of the research are as follows:(1)The alpine swamp wetlands degenerated into alpine meadows,and the total biomass of vegetation,organic carbon,total nitrogen,total phosphorus content and soil p H decreased significantly(P<0.05).The degradation process had a significant effect on some bacteria phyla of low abundance,such as Gracilibacteria and Ignavibacteriae,but had no significant effect on the relative abundance of dominant bacteria phyla.Swamp wetland degradation could significantly increase the relative abundance of Mortierellomycota.The Alpha diversity of soil bacteria and fungi did not show any significant difference in various degradation stages,and the Beta diversity results showed the obvious differences in soil bacterial community structure in different degradation stages.(2)On the daily dynamic level,the degraded stages(light degradation and severe degradation)were significantly higher than non-degradation in photosynthetic rate,respiration rate of ecosystem,net ecosystem carbon exchange and soil temperature,except soil moisture which was substantially lower.The diurnal variation of net ecosystem carbon exchange in different degradation stages is negatively correlated with soil temperature(P<0.05).During the whole peak growth period,the alpine swamp wetland ecosystem was a CO₂ sink,and the carbon sink loss caused by degradation was 193.44±47.01 g·m^-2.(3)There was no significant difference in soil microbial respiration rate between glyphosate spraying and root removal,but the latter reduced soil moisture obviously(P<0.05).Therefore,glyphosate spraying is more appropriate for the determination of soil respiration components.Degradation of alpine swamp wetlands will significantly increase the respiration rate of soil and microbial,and the respiration proportion of vegetation and microbial in the whole ecosystem had been changed significantly.There was a significant positive correlation between vegetation respiration and ecosystem respiration rate in all stages(P<0.05),and there was a positive correlation between root respiration and soil respiration.There was a significant positive correlation between vegetation canopy respiration and ecosystem respiration in non-degradation and severe degradation stages(P<0.05),and there was a significant positive correlation between soil respiration rate,root respiration rate and ecosystem respiration in light degradation(P<0.05).(4)The respiration rate had exponential correlation with soil temperature and positive linear correlation with soil moisture in each degradation stage.The Q10changes in ecosystem respiration,vegetation respiration,canopy respiration,soil respiration,root respiration and soil microbial respiration were 1.41?1.50,1.81?1.94,4.46?6.93,1.41?2.40,2.84?5.97 and 1.99?3.74,respectively.(5)Soil temperature drove the change of CO₂ flow not only on the daily scale,but also on the alpine swamp wetland degradation scale.