Effect Of Iron Oxides On Soil Organic Carbon Stability And Iron-carbon Binding In Aggregates

Soil organic carbon（SOC）is crucial to climate change and soil fertility.The mineralization,sequestration process and stabilization mechanism of SOC are the core of this research.Iron oxides play an important role in promoting the stability of SOC.However,systematic research of iron oxides on soil organic carbon stability mechanism is still limited.In this study,the methods of isotope separation,soil density grouping,iron-bound carbon extraction,aggregate grouping,microbial detection and so on were used,the effect of iron addition on the distribution of mineralization and sequestration was studied by adding different types of substrates（sucrose,corn meal,corn straw）to iron addition（adding amount was 100%of soil iron content）and control soil.By grouping aggregates of gradient iron soil and rhizosphere soil,the dynamic changes and influencing factors of iron and carbon binding in aggregates were studied.The main conclusions are as follows:（1）Fe-addition had inhibition effect on organic carbon mineralization of all treatments,and promoted the substrate sequestration,which made the sequestration mineralization ratio of Fe added soil was higher than control soil.In other words,Fe-addition promoted the stability of SOC from the two aspects of inhibiting mineralization and increasing sequestration.（2）Iron oxide bound organic carbon（Fe-OC）in soil mostly exists in mineral group,and the content of substrate carbon in mineral group determines the tendency of soil carbon fixation.Fe-OC is an important indicator of soil organic carbon stability,and about 1/5 of soil organic carbon is bound by iron oxides.（3）The ratio of Fe-OC to soil organic carbon(f _Fe-OC)was mainly affected by iron oxide in the early stage of incubation,the content of organic carbon in the middle stage,and the combined content of organic carbon and iron oxide in the late stage.In other words,the Fe-addition affected the state of soil aggregates.（4）The stability of rhizosphere aggregates was affected by the addition amount of iron oxides rather than the growth state of plants.Fe-addition deposited organic carbon through the formation of Fe-OC,which affected the activities of microorganisms and enzymes and promoted the stability of soil organic carbon.This paper systematically revealed the important role of iron oxides in SOC stabilization from four aspects:the relationship between iron oxides and organic carbon mineralization and sequestration,the importance of Fe-OC,the change of aggregate state and iron-carbon binding properties of rhizosphere aggregates.