Soil Organic Carbon Composition And Its Influencing Factors In Typical Shoal Wetland Of Poyang Lake

The wetland soil organic carbon pool is one of the most important carbon pools for terrestrial ecosystems,and small changes can have huge impacts on the global climate system.Under the influence of global climate change,the global hydrological pattern has changed drastically,and many long-term flooded wetlands have been transformed into seasonally flooded wetlands.A large amount of soil organic carbon in wetland soils is at risk of oxidative decomposition.However,it is now impossible to assess this risk.One of the most important reasons is that the stability and protection mechanisms of soil for organic carbon in seasonally flooded wetlands are still unclear.Therefore,in this study,four lakeshore wetlands with different flooding rhythms and soil properties,including Benghu,Dahuchi,East Lake and Baisha Lake,were selected as sample plots,and 288 soil samples were collected from three vegetation zones（mudflat zone,wet vegetation belt and emergent vegetation zone）and three depths（0-10 cm,10-20 cm,20-30 cm）along the flooding duration gradient,and the spatial heterogeneity of soil organic carbon physicochemical components was comprehensively analyzed.The effects of soil organic carbon chemical composition,aggregate closure,soil physicochemical properties and mineral adsorption on SOC in typical seasonal flooded wetlands were clarified.The main results of this study are as follows.（1）In the four continental wetlands,soil organic carbon（SOC）ranged from1.12-149.26 mg/g,and the average value was 17.09 mg/g.The SOC content of Benghu,Dahuchi and East Lake were all affected by the vegetation zone,but the SOC content of Baisha Lake was not affected by the vegetation zone.In general,the SOC of the mudflat zone of the Zhoutan wetland was significantly lower than that of the wetted vegetation zone and the emergent vegetation zone.SOC is also significantly affected by soil depth.In the four Zhoutan wetlands,there were 0-10cm>10-20 cm>20-30 cm regularities.（2）In the four Zhoutan wetlands,the ranges of dissolved organic carbon（DOC）and microbial biomass carbon（MBC）were 24.35-406.01 mg/kg and 32.51-1966.64mg/kg,respectively,and the average values were 108.25 mg/kg and 733.34 mg/kg,respectively.Both DOC and MBC were significantly affected by the Zhoutan wetland,and their distribution in the vegetation zone was basically consistent with the distribution of SOC.（3）In the four Poyang Lake Zhoutan wetlands,the content of microaggregates was relatively higher,and a large amount of SOCs were stored in large aggregates.In the four Zhoutan wetlands,the contribution rates of large aggregates,microaggregates and powder+clay particles to SOC reserves were 34.40%,39.30%and 24.67%,respectively.The contribution rate of large aggregates and powder+clay to SOC storage was affected by vegetation zone and soil depth,but the contribution rate of microaggregates to SOC storage was only significantly affected by soil depth.（4）In the soil 288 samples of four Flat wetlands,free iron oxide,amorphous iron oxide and complex iron oxide ranged from 75.86 mg/kg-2719.42 mg/kg,19.18 mg/kg-1075.52 mg/kg and 0.95 mg/kg-136.78 mg/kg,respectively,with mean values of 693.16 mg/kg,423.24 mg/kg and 33.75mg/kg,respectively.Vegetation zone and depth had significant effects on free iron oxide,amorphous iron oxide and complex iron oxide,but depth had no significant effect on free iron oxide.Free iron oxide and amorphous iron oxide showed mudflats>wetted vegetation zones>emergent vegetation zones between vegetation zones.The complexed iron oxide showed a mudflats and emergent vegetation zones<wetted vegetation zones,Both amorphous iron oxide and complex iron oxide showed a pattern of 0-10 cm>10-20 cm>20-30 cm in soil depth.（5）SOC has a strong positive correlation with TN,and also has a positive correlation with TP,NO₃^--N,NH₄⁺-N,SM and Eh,and negatively correlated with p H.In addition,the average weight diameter（MWD）,geometric mean diameter（GMD）and complexed iron oxide of agglomerates all had positive correlations on SOC,while powder+sticky content were negatively correlated with SOC.In summary,the stability of soil organic carbon in wetlands was significantly affected by seasonal flooding.The results of this study will provide a reference for clarifying the carbon cycle process in Poyang Lake.In summary,the content of soil organic carbon in wetlands was affected by topography and vegetation carbon input,and the stability of soil organic carbon was affected by soil physical and chemical factors,soil aggregates and soil iron oxides.The results of this study will provide data support for clarifying the carbon cycle process of Poyang Lake and the assessment of wetland carbon sinks.