Study On The Relationships Between Soil Iron And Carbon Of The Typical Degraded Wetlands In Sanjiang-Songnen Plain

The increasing of greenhouse gases concentrations in the atmosphere leads to global warming.As the most important carbon?C?pool of terrestrial ecosystem,soil can reduce the amount of CO₂ emitted into the atmosphere by stabilizing more C.In this way,the trend of global change can be slowed down and the global warming situation can be alleviated.There are numerous factors that affect accumulation of organic carbon?OC?in soils.Among them,iron?Fe?plays an essential role in"capturing"organic carbon and forming"rusty sink",thus promoting accumulation of soil organic carbon?SOC?.By summarizing the previous research results,it is found that there are four protection mechanisms of SOC including physical preservation of aggregates,chemical preservation of minerals,biological preservation of microorganisms and preservation of organic carbon per se,and the former two are the main ones.Fe is closely involved in the physical,chemical and biological protection mechanism.In order to explore the relationships between Fe and C in the soil of wetlands in northeast China,a comparative study was conducted between degraded freshwater marshes in the degraded saline-alkali marshes in the Momoge National Nature Reserve?MNR?located in the Songnen Plain,Jilin province and the Sanjiang Mire Wetland Experimental Station of the Chinese Academy of Sciences?SJM?located in the Sanjiang Plain,Heilongjiang Province.The relationships between Fe and C in the soil includes:concentrations of TFe,different forms of iron oxides,SOC,DOC and MBC,weathering index,aggregate index,basic physical and chemical properties and the stabilizing effect of Fe on OC?the percent of OC stabilized by Fe in total OC concentrations,represented by Fe-OC effect?.First,the soils under three vegetation types,Phragmites australis,Scirpus planiculmis and Suaeda glauca,were studied in MNR.By comparing the Fe and C concentrations and basic physical and chemical properties of soil under different vegetation types in degraded saline-alkali marsh,it was concluded that except soil moisture,there were no significant differences in Fe and C concentrations and basic physical and chemical properties in degraded saline-alkaline marsh wetland soils?p<0.05?.Soil aggregate structure was the most stable in P.australis,followed by S.planiculmis and S.glauca.The Fe and C concentrations of soil aggregates under three vegetation types were consistent with the change trend of aggregate size.The Fe-OC effect in soil was P.australis>S.planiculmis>S.glauca,but the difference was non-significant?p<0.05?.Second,the soils under the six land use/cover types of freshwater marsh wetland were studied in SJM.The six types are soybean land,paddy field,15-year restoring wetland?restoring wetland A?,18-year restoring wetland?restoring wetland B?,22-year restoring wetland?restoring wetland C?and natural wetland.Results showed that except pH and moisture concentrations,Fe and C concentrations and basic physical and chemical properties of different land use types were significantly different?p<0.05?.The natural wetland had the highest soil fertility and the best soil aggregate structure.The soybean soil had the lowest soil fertility and the soil aggregate structure was the worst.In the natural wetland,the Fe-OC effect was the weakest while stronger effects could be observed in the soybean field and the restoring wetland C.Under the six types,the Fe and C concentrations in the soil aggregates were consistent with the change of the aggregate size.Through comparative studies,the differences in soil Fe,C concentrations and basic physical and chemical properties between the two study areas can be found.This can explain the similarities and differences of Fe-OC relationships and explain the mechanisms of Fe stabilizing OC.The soil under the three vegetation types represents the degraded saline-alkaline marsh wetland in MNR,and the soil under the six land types represents the degraded freshwater marsh wetland in SJM.A comparative study in the two study areas showed that the soil pH in SJM was much lower than that in MNR,and the former water concentrations were much higher subject to a long-term reduced conditions.In addition,the soil aggregate structure of the freshwater marsh wetland soil was stable,and that of the saline-alkaline marsh wetland was brittle.The Fe-OC effect in freshwater marsh wetland soil was stronger than that in saline marsh wetland,but the difference is not significant?p<0.05?.Finally,the factors that influencing Fe-OC effect were analyzed.The results showed that the increase of pH and C/Fe could inhibit the Fe-OC effect.