Mechanism Of Different Forms Of Nitrogen On Regulating Corn Straw Decomposition

Crop straw returning to the field can improve soil physical and chemical properties,increase crop yields,and promote the nutrient resources recycling and sustainable agricultural development.However,low crop straw decomposition and nutrient utilization efficiency resulted from the large amount of straw returned to the field and well as microorganisms compete with crops for nitrogen,which showed that the accelerating crop straw decomposition is a key step to recycling straw nutrient resources.Previous studies mainly focused on the effects of introducing microorganisms and adjusting C/N in crop straw decomposition,but there is still a lack of deeply systematic studies on the effects of different forms of nitrogen in straw decomposition and its microbial mechanism.In this study,the nylon mesh bag method was used to analy the influences of different forms of nitrogen,such as ammonium bicarbonate,ammonium sulfate,calcium nitrate,urea and glutamate in the corn straw decomposition were studied by using the simulated nylon mesh bag method in the Lab.The treatment without nitrogen addition as was conducted as a control(CK).The decomposition rate and nutrient release from corn straw,the structure and diversity of microbial communitiesas well as the enzyme activities related to the degradation of cellulose and lignin components in corn straw were analyzed.The fungi and bacteria for efficient degradation of corn straws were screened,and its potential mechanism were also explored.The main results are as follows:(1)The residual mass of corn straw was gradually decreased with the extension of the cultivation time after adding different forms of nitrogen,and glutamate,ammonium sulfate and ammonium bicarbonate promoted the decomposition of corn straw.The effects of glutamate on promoting corn straw degradation was higher than other N forms.The nutrient release rate of corn straw duiring the process of decomposition followed the order of potassium> phosphorus> nitrogen.The gradually decrease of carbon,nitrogen,phosphorus and potassium residual mass of corn straw treated with different forms of nitrogen addition.Glutamate is the best N form in promoting the release of carbon,nitrogen and potassium,while ammonium sulfateis is the best N form in promoting the release of phosphorus in corm straw.(2)The results of NMR showed that the relative contents of alkoxy carbon and anomeric carbon functional groups in the corn straw gradually decreased with the decomposition,whereas relative contents of the aromatic carbon,methoxy carbon,alkyl carbon,phenolic carbon and carboxyl/amino groups iwere enriched is the process of corn straw decomposition.Ammonium sulfate promoted the degradation of organic carbon with alkyl carbon,carboxyl/amino and ketone aldehydes in corn straw,whereas inhibited the degradation of organic carbon with alkoxy,anomeric carbon and methoxy carbon functional groups.Glutamate promoted the degradation of organic carbon with alkoxy and ketone aldehydes,whereas inhibited the degradation of organic carbon with aromatic carbon,methoxy carbon and aromatic carbon functional groups.Urea promoted the degradation of organic carbon with ketone aldehydes,whereas inhibited the degradation of organic carbon with anomeric carbon,aromatic carbon and phenolic carbon functional groups.(3)The abundance and diversity of bacteria were significantly reduced by ammonium sulfate addition,but there were no significant difference in other N form treatments.The relative abundance of Actinobacteria were significantly increased by ammonium sulfate addition in the early stage of corn straw decomposition,and significantly increased the relative abundance of Proteobacteria in the middle and late stages;urea significantly increased the relative abundance of Bacteroidetes in the early and mid-stage of corn straw decomposition.The relative abundance of Bacteroidetes and Firmicutes was significantly promoted in the early and middle period of incubation,and the relative abundance of Gemmatimonadetes was significantly promoted in the later period.(4)The abundance and diversity of fungi were reduced in the decomposed corn straw with exogenous nitrogen addition.Ammonium sulfate significantly reduced the relative abundance of Ascomycota and Mucoromycota;urea significantly reduced the relative abundance of Ascomycota and Mucoromycota,while significantly increased the relative abundance of Chytridiomycota.Glutamate significantly increased the relative abundance of Ascomycota,and decreased the relative abundance of Mucoromycota.(5)The activity of β-GC(β-Glucosidase)was inhibited by Glutamate,while it was increased by ammonium sulfate in corn straw decomposition.The activity of NEX(Neutral Xylanase)was inhibited by the exogenous nitrogen addition in the middle stage of corn straw decomposition,while ammonium sulfate increased the activity of NEX at the later stage of straw decomposition.As for Laccase(Lac)activity,Ammonium sulfate and urea greatly increased it at the early and mid-stage of corn straw decomposition,while glutamate promoted it at the mid-stage of corn straw decomposition.The addition of external nitrogen also increased the activity Lignin peroxidase(Lip)at the late stage of corn straw decomposition,especially the urea addition.(6)The results of Structural equation modeling(SEM)analysis indicated that the glutamate addition could increase the degradation rate of corn straw mainly by regulating the activity of Lac and β-GC,which regulated by the relative abundance of Bacteroidetes Gemmatimonadetes,respectively.The addition of ammonium sulfate can regulate and increase the relative abundance of Actinobacteria and Proteobacteria,and then affect the activities of β-GC and Lac to promote the corn straw degradation.(7)Seventeen strains of high-efficiency cellulose degrading bacteria were screened by using the CMC-Na plate method,all of which have the ability to produce NEX,β-GC and Cellulase(CL).Actinobacteria and Proteobacteria were the dominant phylums in bacterial community,while it was predominanted by Ascomycota in fungi with ammonium sulfate addition.Actinobacteria and Proteobacteria could secretes NEX and CL,Proteobacteria could secretes β-GC,and Ascomycota secretes NEX.In glutamate-treated corn straw,bacteria mainly include Actinobacteria,Firmicutes and Proteobacteria,while fungi predominanted by Ascomycota.Actinobacteria could secretes β-GC,Firmicutes and Ascomycota could secretes NEX,and Proteobacteria secretes NEX and β-GC.(8)Twelve high-efficiency lignin-degrading bacteria were screened through the aniline blue plate method,all of which have certain ability to produce Lac and Lip.Bacteria community was predominanted by Proteobacteria while fungi community was predominanted by Ascomycotain during the corn straws decomposition with ammonium sulfate addition.Ascomycota and Proteobacteria could secretes Lip and Lac;Bacteria mainly composed by Actinobacteria and Proteobacteria while fungi mainly composed by Ascomycota and Mucoromycota in corn straws decomposition with glutamate addition.Proteobacteria and Ascomycota could secrete Lip and Lac,Actinobacteria could secretes Lac,and Mucoromycota could secretes Lip in decomposed corn straw.