The Mechanism Of Organic Material And Desulfurized Gypsum Amendment On Organic Matter In Saline-sodic Soils

Saline-sodic soil in Northeast China is a potential arable land resource with tremendous development and utilization potential.High soil salinity,exchangeable sodium content,and organic matter deficiency are limiting factors for its development and utilization.The addition of exogenous calcium and organic materials is key to addressing these issues.However,the response of organic matter in saline-sodic soils to the addition of exogenous materials is not yet thoroughly investigated.To comprehensively study the effects and improvement of desulfurized gypsum and organic material addition on soil organic matter in saline-sodic soils,this study conducted research and discussions in the following aspects:In the first part,through controlled leaching experiments,the characteristic changes of soil organic matter and their influencing factors during the leaching process with the combined application of organic materials and desulfurized gypsum were explored.In the second part,through soil incubation experiments,the dynamic changes of soil carbon emissions and their influencing factors with the combined application of organic materials and desulfurized gypsum were investigated,and the changes in microbial community were analyzed.The changes in soil aggregate stability,organic matter content,and organic matter composition and their influencing factors were studied.In the third part,field experiments were conducted to study the effects of combined application of lignite humic acid and desulfurized gypsum on soil organic matter and crop yield in saline-sodic paddy fields.The main conclusions are as follows:（1）Dissolved organic matter（DOM）leaching losses were significantly higher in treatments with lignite humic acid,cattle manure,and desulfurized gypsum compared to straw treatment.Fluorescence and ultraviolet spectroscopy analysis showed that the proportion of exogenous DOM was relatively high during the leaching process.The leachate from straw treatment contained relatively higher proportions of C1,C3,and C4 components,while the leachate from lignite humic acid and cattle manure treatments had a higher proportion of the C2 component.RDA analysis showed that changes in soluble ion content could explain 73.43%of the variation in DOM,with HCO₃^-having the greatest impact on DOM content and properties.（2）Different types of organic materials had different effects on soil CH₄ and CO₂ emissions.Straw and cattle manure treatments significantly increased the emission rates and cumulative emissions of both gases,while lignite humic acid treatment only promoted CO₂ emissions.The addition of desulfurized gypsum reduced CH₄ emissions and increased CO₂ emissions.Correlation analysis revealed that bacterial diversity was significantly negatively correlated with the total emissions of CH₄ and CO₂,while fungal diversity was significantly positively correlated with the total emissions of CO₂.Bacterial diversity was significantly negatively correlated with p H,CO₃^2-,HCO₃^-,and significantly positively correlated with Mg²⁺,Ca²⁺,and EC,as well as negatively correlated with cellulase and laccase.Fungal diversity was significantly positively correlated with p H,CO₃^2-,and negatively correlated with Na⁺,as well as positively correlated withβ-glucosidase and negatively correlated with cellulase.（3）There were significant differences in soil microbial community structures among different treatments,and the total emissions of CO₂ and CH₄ were significantly correlated with changes in soil microbial community.Variance decomposition analysis showed that the variation in bacteria was explained by47.60%and 12.1%by the type of organic materials and desulfurized gypsum,respectively,while for fungi,it was explained by 16.00%and 3.5%by the type of organic materials and desulfurized gypsum,respectively.The importance of soil microbes in CH₄ and CO₂ emissions at the OTU level was evaluated using a random forest regression model.The results showed that OTUs belonging to the phyla Archaea and Actinobacteria played a key role in the construction of CH₄ and CO₂related emitting microbial communities.（4）The combined application of organic materials and desulfurized gypsum increased the proportion of 2-0.25 mm aggregates in saline-sodic soil and increased the mean weight diameter of soil aggregates.Soil organic matter content was mainly influenced by the addition of organic materials.Lignite humic acid,straw,cattle manure,and desulfurized gypsum treatments increased the content of aromatic compounds in the soil and improved the stability of soil organic matter.Desulfurized gypsum treatment increased the content of polycyclic aromatic hydrocarbons,while cattle manure treatment increased the content of nitrogen compounds.Straw and lignite humic acid treatments reduced the content of nitrogen compounds and lignin derivatives.Lipids and polysaccharides were not significantly affected.The effects of different organic materials and desulfurized gypsum on organic matter composition varied in different soil particle sizes,and the impact on organic matter composition was significant in the>0.25 mm particle size soil.（5）The combined application of lignite humic acid and desulfurized gypsum significantly reduced soil salinity,total alkalinity,and p H values,increased soil organic matter content,improved the calcium-sodium displacement efficiency of the soil,optimized its yield components,and increased rice yield.Soil organic matter and total alkalinity were the main environmental factors affecting soil microorganisms during the improvement process.In summary,the study on the leaching,mineralization,distribution,and improvement of organic matter in saline-sodic soil with the combined application of organic materials and desulfurized gypsum revealed the short-term changes in soil organic matter during the improvement process,clarified the interactions among biological,physical,and chemical properties of saline-sodic soil and soil organic matter,and provided theoretical support for the management and utilization of saline-sodic soil.