| Returning straw to biochar is one of the effective ways to solve the low utilization rate of agricultural waste.A large number of studies have shown that biochar can have various beneficial effects on the soil environment.As the preparation process of hydrochar is more economical,simple and efficient,it has good application prospects.However,some dissolved organic matter(DOM)in hydrochar may have a certain toxic effect on the soil environment,and its impact on the soil environment is not clear,which greatly limits the application of hydrochar in soil.Soil DOM is composed of various compounds and is of great significance in the soil ecological environment.While applying biochar to the soil will improve the soil environment,it will also bring some of its own harmful substances into the soil.At present,there is little research on the influence of biochar on soil DOM,and exploring the impact of biochar on DOM can further understand the positive or negative effects of biochar on the soil environment.Studies have found that iron oxides can eliminate some of the adverse effects of soil DOM.If the mixed application of iron oxide and hydrochar can improve the soil environment,it can also reduce the toxic effect of hydrochar,which will increase the utilization of hydrochar.However,research in this area is relatively vacant and it is necessary to explore it.In view of this,in this study,brown soil in the north was selected,and iron oxides and hydrochar and pyrolysis prepared by corn stalks were used for indoor culture experiments,to study the effects of iron oxides and biochar on soil chemical properties and analyze their possible effects on soil fertility;Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR MS)method was used to obtain detailed information of single molecules in complex mixtures,and to explore the effect of iron oxides and biochar on the chemical diversity of DOM molecules in soil;High-throughput sequencing was used to detect changes in soil microbial diversity and community structure before and after the addition of iron oxides and biochar,and to explore the effects of biochar on soil microbial diversity and community structure.The aim is to provide some theoretical basis for the convenient and efficient application of hydrothermal charcoal to soil environment.The main findings are as follows:(1)Both hydrochar and pyrolysis char can affect soil nutrients to varying degrees.Both hydrochar and pyrolysis can significantly increase soil p H,DOC,available potassium,total nitrogen and total phosphorus contents.Mixed application of iron oxide with hydrochar or pyrolysis will reduce soil p H,nitrate nitrogen,ammonium nitrogen,available potassium,total phosphorus and other soil nutrients.Hydrochar will reduce the content of soil sucrose,urease,catalase and β-glucosidase to varying degrees.The pyrolysis significantly increased the content of sucrose and catalase.the mixed application of iron oxide and hydrothermal carbon or pyrolytic carbon can significantly increase the content of catalase.(2)Hydrochar and pyrolysis can affect the molecular composition of soil DOM.Pyrolysis carbon and its mixed treatment with iron oxides increase the aromaticity and chemical bond unsaturation of soil DOM molecules,and enhance the resistance to decomposition.The mixed treatment of hydrochar and oxides can promote the deoxidation of related compounds and produce compounds with lower oxygen numbers,generate DOM molecules with lower molecular weight and carbon number,further degrade aromatic compounds and produce more aliphatic compounds.Under the treatment of hydrochar and pyrolysis,the molecular diversity and complexity of the compound increase.But iron oxide can remove macromolecular compounds produced by hydrochar.(3)The lignin/CRAM-like compounds accounted for the largest proportion under each treatment,followed by fused ring aromatics or tannins.Hydrochar can increase the ratio of soil DOM lignin/CRAM-like structural compounds and carbohydrates,and reduce the ratio of condensed aromatics,tannins and so on.Iron oxide can increase the proportion of lipids,aliphatics/proteins,and unsaturated hydrocarbons that are suppressed by hydrochar,and further reduce the proportion of condensed aromatics and tannins.In addition,the mixed application of iron oxide and hydrochar can also reduce the molecular complexity of lignin/CRAM-like compounds,condensed aromatics and tannins.Pyrolysis can increase the ratio of condensed aromatics and tannins and reduce the ratio of lignin/CRAM-like compounds,lipids and so on.Iron oxides can increase the ratio of lignin/CRAM-like compounds,lipids and so on that are suppressed by pyrolysis,and further increase the tannin ratio.(4)The addition of iron oxide and biochar changed the composition and structure of the bacterial community,and the effect of iron oxide on the community structure was small.The abundance and diversity of soil bacteria under pyrolysis treatment are significantly higher than those treated with hydrochar,but the addition of iron oxide can increase the bacterial abundance and diversity under hydrochar treatment.It shows that the mixed application of iron oxide and hydrochar can offset some of the adverse effects of hydrochar on soil bacterial community.(5)The addition of iron oxide and biochar changed the composition and structure of the fungal community.Moreover,hydrochar and its mixed application with iron oxides have a greater impact on the community structure.The abundance and diversity of soil fungi treated with pyrolysis were significantly higher than those treated with hydrochar.But the addition of iron oxides could increase the fungal abundance and diversity under pyrolysis,it shows that the mixed application of iron oxide and hydrochar can offset some of the adverse effects of hydrochar on soil fungal communities.(6)RDA analysis found that soil DOC and total nitrogen were the main environmental factors affecting Actinobacteria and Proteobacteria.p H is the main environmental factor that affects the abundance of Acidobacteria,Chloroflexi,Gemmatimonadetes,Planctomycetes,Basidiomycota,and Mortierellomycota.The contents of soilβ-glucosidase,urease,and sucrose are related to the abundance of bacteria such as Gemmatimonadetes,Acidobacteria,Chloroflexi and Fungi Basidiomycota,Mortierellomycota,and catalase mainly closely related to the bacterial Verrucomicrobia and Actinobacteria.Through network analysis,it was found that Acidobacteria,Chloroflexi in bacteria and Ascomycota,Basidiomycota,and Mortierellomycota in the fungus,were positively related to lipids.Proteobacteria in bacteria is positively correlated with carbohydrates.Acidobacteria,Chloroflexi in bacteria and Mortierellomycota in fungus are all negatively related to lignin/CRAM-like compounds.Actinobacteria,Proteobacteria in bacteria and the three dominant phylums of the fungus,which are Ascomycota,Basidiomycota,and Mortierellomycota,were all negatively related to tannins. |
