Characteristics And Mitigation Measures Of Organic Carbon Mineralization In Degraded Wetland Soils In Mu Us Sandy Land

Since the 21st century,global greenhouse effect has intensified,global climate has warmed,and atmospheric CO₂ concentration has risen sharply.At the same time,there is a trend of rapid degradation of wetland worldwide.Desert wetland is one of the ecosystems with the highest carbon density and has the reputation of"desert oasis".The degradation of desert wetlands will inevitably lead to the risk of carbon emission.Our research on wetland degradation mainly focuses on coastal wetlands and forest wetlands,with less research on wetlands in arid and semi-arid areas.Meanwhile,iron oxides as soil amendments to increase soil carbon fixation capacity have been used mainly in rice fields,but less in desert wetlands.Wetland water loss is the direct cause of wetland degradation.Therefore,this paper takes the wetland of Mu Us Sandy area as the research object to study（1）soil nutrient content,soil microbial community changes and carbon emission characteristics of non-degraded wetland（ND）,mildly degraded wetland（LD）,moderately degraded wetland（MD）and severely degraded wetland（SD）at different degradation stages.（2）Study the effects of different water conditions of 30%WHC,60%WHC,90%WHC,0.5 cm,1cm and 3 cm in wetland on soil organic carbon conversion and soil organic carbon mineralization,and clarify the soil organic carbon conversion process in the process of wetland degradation.（3）Adding 60 mg of iron oxide（20%of the total iron content of the soil）to the soil for anaerobic culture.Taking no added iron oxide as the control,the influence of adding iron oxide on soil organic carbon mineralization in wetland was analyzed,the interaction between iron reduction process and organic carbon mineralization process was understood,and the inhibiting effect of iron oxide on wetland carbon emission process was discussed.A technical system for adding iron oxide to slow down wetland carbon emission was proposed to provide a theoretical basis for the stability of local wetland carbon pool and ecological restoration.The main conclusions are as follows:（1）With the degradation of wetland,soil organic carbon mineralization decreases rapidly,and a large amount of C in soil was released.In the mild degradation stage,soil changed from flooded state to good gas state,and soil organic carbon mineralization reached the maximum with 0.49 mg·kg^-1.In the severe degradation stage,soil organic carbon mineralization reached the minimum with 0.04 mg·kg^-1.Compared with the non-degraded stage,soil moisture,organic carbon（SOC）,total nitrogen（TN）,ammonium nitrogen（NH₄⁺-N）and microbial carbon（MBC）contents decreased significantly in the severely degraded stage,by 95%,96%,94%,88%,94%,respectively.However,soil p H and NO₃^--N content showed an increasing trend,p H increased by 35.47%,NO₃^--N content increased by 17.08 mg·kg^-1.With the process of wetland degradation,soil total phosphorus content first decreased and then increased,and soil dissolved organic carbon（DOC）content first increased and then decreased.Shannon and Chao1 indices of prokaryotic cells were lowest in SD and higher in LD,but no significant changes were observed among ND,LD and MD（p<0.05）,the similarity of prokaryotic microbial community gradually decreased with the increase of wetland degradation,and the degradation of wetland changed the prokaryotic microbial community and functional composition.（2）The cumulative mineralization amount of soil organic carbon in deep flooded soil was significantly lower than that in shallow flooded soil,and increasing the depth of flooding could significantly inhibit soil organic carbon mineralization.After exposed soil in degraded wetlands,soil organic carbon mineralization can be inhibited if the soil moisture content is too high（90%WHC）or too low（30%WHC）,and the soil organic carbon mineralization can be maximum only under the suitable water condition（60%WHC）.（3）The addition of iron oxides in wetland soil can effectively inhibit the mineralization of soil organic carbon,and the addition of iron oxides in wetland soil can reduce the emission of carbon dioxide,which is conducive to the accumulation of soil organic carbon and increase the carbon sequestration effect of wetland.In summary,the degradation of Mu Us wetland will lead to the decrease of soil nutrient content,the enhancement of soil organic carbon mineralization,the increase of wetland net carbon emission,the change of microbial species,quantity and community,and the influence of water on soil organic carbon mineralization is relatively complex.Under good air conditions,low or high water content will inhibit soil organic carbon mineralization.Under flooded conditions,The cumulative mineralization of organic carbon in deep flooded soil was significantly lower than that in shallow flooded soil.Increasing the depth of flooding could significantly inhibit the mineralization of soil organic carbon.Therefore,increasing the depth of wetland flooding and the content of iron oxide in soil can reduce the mineralization of soil organic carbon and reduce the risk of wetland carbon emission.