Effect Of Iron Oxide On Methane Emission And Priming Effect Of Paddy Soil

Paddy soil is one of the important sources of methane emission.The anaerobic degradation of organic matter such as rhizosphere secretions and crop residues and its stimulating effect on soil organic carbon are the key ways of methane emission.However,related research is scarce.The subtropical paddy soil is rich in iron,and iron is an important element affecting the redox environment of paddy soil.Its reactivity is significantly affected by the crystal form,and the mechanism of the effect on the excitation effect of methane production in paddy soil is still unclear.Therefore,this project intended to use subtropical paddy soil as the research object,using indoor culture and ¹³C stable isotope tracer technology to study the dynamic changes of methane emission from paddy soils with different crystalline iron oxides,and quantify the methane excitation effect,combined with soil physical and chemical properties and enzyme activity to dissect the driving mechanism of iron oxides affecting methane production and excitation effects in paddy soils.The main conclusions were as follows:?1?The addition of iron oxide inhibited the methane emission from paddy soil,which is related to the fixation of iron oxides to CO₂,the competition for substrates and electrons,and the activity of iron-reducing bacteria.The strength of the inhibition was specifically manifested as no inhibition in the early stage of culture,strong inhibition in the middle of culture,and weak inhibition in the later stage of culture.Correlation analysis also showed that soil Fe²⁺content had a significant negative correlation with CH₄ cumulative excitation effect,SOM-mineralization rate and CH₄ cumulative release?P<0.01?.?2?The inhibitory effect of ferrihydrite on methane emission from paddy soil was stronger than that of goethite,indicating that different iron oxides had different degrees of inhibition on methane.This inhibition was mainly related to the degree of mineral crystallization,the lower the degree of crystallization,the higher the reactivity,and the higher the degree of iron reduction,the stronger the inhibition of methane.?3?Iron oxide significantly inhibits the cumulative emission of CH₄ from exogenous carbon sources,that related to the adsorption of iron oxide on acetic acid.The inhibitory capacity of ferrihydrite is higher than that of goethite.The possible reason is that the specific surface area of ferrihydrite is much larger than the specific surface area of goethite,which leads to stronger adsorption.?4?The addition of exogenous acetic acid promoted the mineralization and decomposition of the original organic carbon in the soil to release methane,which was represented by the positive methane excitation effect;On the basis of the addition of acetic acid,the addition of ferrihydrite enhanced this positive excitation effect.The possible reason is that the carboxyl group in acetic acid is easily adsorbed with ferrihydrite,The substrate that can be used by methanogens is reduced,thus accelerating the anaerobic degradation of the original organic matter of the soil to obtain the substrate to meet its own needs,thus exhibiting a tendency to enhance the positive excitation effect of methane.?5?There was a significant positive correlation between the cumulative release of CH₄and the cumulative excitation effect of CH₄,SOM-mineralization rate,The correlation coefficients respectively were 0.853 and 0.933.This indicated that the release of methane was mainly derived from the mineralization and decomposition of the original organic carbon in the soil.