Biological And Chemical Mechanism Of Mn²⁺ Impacting On Wheat Straw Decomposition

Straw returning can not only regulate soil fertility and physical properties,but also optimize the farmland ecological environment and reduce agricultural resources waste.Straw returning methods include direct returning and composting.There are many studies on the effects of adding microbial agents,industrial waste residues or livestock manure on nutrient release and decomposition quality in straw composting.However,there are few reports on the effects of adding micro-element nutrients on the changes of material structure and microbial enzymatic activity in the process of straw composting.In this experiment,net bag culture method was used to study the effects of different concentrations of manganese ion on the decomposition and nutrient release from straw at different adding time.The relationship between the change of sugars,lipids and lignin and the concentrations of manganese ions in the decomposition straw residues was analyzed by FTIR technology.Changes of ligninase,cellulase and hemicellulase activities during decomposition in wheat straw residues under different concentration of manganese ions was determined by microbial detection kit methods.The microbial community was also determined by 18s high-throughput sequencing method.The main results are as follows:1、The residual amount of wheat straw showed a rapid decline in the early stage,a slow decline in the medium term,and a gradual stable trend in the later stage.The addition of 0.25 mg/g Mn2+ increased the decomposing rate of wheat straw and promoted the carbon release in the early stage of wheat straw decomposing,whereas the addition of 2.0 mg/g Mn2+inhibited the degradation of wheat straw.2、The addition of 0.25 mg/g Mn2+promoted the degradation of sugars in wheat straw,while increased the relative contents of aromatic hydrocarbons(C=C)and carboxylate(COO-)in wheat straw residues,as well as improved the oxidation and aromatization degree of decomposed wheat residues,but reduces its aliphaticity.3、The addition of 0.25 mg/g Mn2+ can increase the activity of neutral xylanase(NEX)in the early stage of decomposing,while increase the activity of manganese peroxidase(MnP)and lignin peroxidase(LiP)in the late stage of decomposing,and increase the activity of laccase in the early stage of decomposing,and have no significant effect on the activity of carboxymethyl cellulase and β-glucosidase.4、The addition of 0.25 mg/g Mn2+increased the diversity of microbial communities and increased the abundance of pre-decomposing species.At the level of phylum classification,the addition of 0.25 mg/g Mn2+ increased the relative abundance of Basidiomycota and reduced the relative abundance of Ascomycota in the late stage of decomposing.At the level of genus classification,the addition of 0.25 mg/g Mn2+increased the relative abundance of Coprinopsis,and increased the relative abundance of Chaetomium in the early stage of decomposing.5、Multiple regression and path analysis results show that manganese peroxidase and lignin peroxidase are the main decision factors affecting the quality of wheat straw,element release and changes in sugar,aromatic and fatty substances,whereas the Neutral xylanase is the main decision factor affecting the change of fatty substances.