Effects Of Different Maize Straw Return Methods On Organic Carbon Fraction And Microbial Diversity In Chernozem

In recent years,with the vigorous promotion of straw return technology,different straw return methods are being widely promoted and applied in Northeast China.In order to clarify the feasibility of different straw return methods in agricultural production,we set up CK(no straw application),SP(straw ploughing),SM(straw mulching),SG(straw granulated return),EIS-20(even incorporation of straw to 0.2 m soil depth),EIS-40(even incorporation of straw to 0.4 m soil depth),and EIS-60(even incorporation of straw to 0.6 m soil depth)in chernozem of northeast China as the research object.The effects of different straw return methods on active organic carbon,inert organic carbon and agglomerated organic carbon at different soil depths(0-20 cm,20-40 cm,and 40-60 cm)in chernozem were investigated by a combination of chemical and physical separating methods;The structure of bacterial and fungal communities of chernozem were investigated by high-throughput sequencing technology in order to elucidate the characteristic patterns of microbial community changes on the accumulation of soil organic carbon and the hierarchical structure of soil aggregates,and to provide a theoretical basis for the rational determination of the best straw harvesting method for northeast China.The main research results and conclusions are as follows.1.Straw return effectively promoted the accumulation of total organic carbon,active organic carbon fraction,and inert organic carbon fraction in the surface soil,in which EIS-20 and SG treatments significantly increased soil SOC and HAC content compared with other straw return treatments;while EIS-20 also significantly increased DOC,EOC and MBC content compared with other straw return treatments;and SM treatment had the highest FAC content.However,for the 20-40 cm and 40-60 cm soil layers,the SP treatment had higher SOC,HAC,and FAC contents,and the SG treatment had higher MBC contents in the 20-40 cm layer;the effect of straw mulching on deeper soils was weaker;while the EIS-40 and EIS-60 treatments had higher contents in all chemical fractions of organic carbon.2.Straw mulching effectively improved the structural composition of soil aggregates at all levels and significantly increased the organic carbon content of some aggregates.In the 0-20 cm soil layer,SG and EIS-20 had significant effects on the mass ratio and organic carbon content of LM,MA,m M-POM,and m M-SC fractions.In the 20-40 cm and 40-60 cm soil layers,both EIS-40 and EIS-60 treatments effectively contributed to the increase in the mass ratio and organic carbon content of LM,MA,MA(c)POM,m M,m M-POM,and m M-SC fractions.In addition,the mass ratio and organic carbon concentration of m M-POM and m M-SC fractions of EIS-20 treatment had a large degree of decrease with increasing soil depth.3.Straw return effectively promoted the molecular structural changes of HA and FA in topsoil,among which EIS-20 had the most obvious change effect,followed by SG and SM.Compared with other treatments,EIS-20 significantly promoted the decomposition and transformation of maize straw,increased the contents of aliphatic compounds,amides and carbohydrates in soil HA,and made the molecular structure of HA and FA more simplified in soil.However,SP,SG and SM treatments increased the content of aromatic compounds in soil HA,and increased the aromaticity and condensation degree of soil HA and FA.4.SG and EIS-20 treatments effectively promoted the increase of Alkyl-C and O-alkyl-C in surface soil,increased the ratio of aliphatic C/aromatic C,enhanced the aliphatic of organic carbon molecules,and made the molecular structure of soil organic carbon tend to be simpler and younger.However,with the gradual increase of soil depth,the proportion of Methoxy-C and O-alkyl-C gradually decreased in soil,while the proportion of Aryl-C gradually increased.Moreover,EIS-60 in the 20-40 cm and 40-60 cm soil layers effectively promoted the formation of long-chain complex fatty carbon in soil organic carbon,driving the renewal and activation of organic carbon in the deep soil layer,and improving the thermal stability of the soil to some extent.5.SM and SG effectively contributed to the increase of bacterial community abundance in the surface soil,while EIS-40 and EIS-60 had the highest bacterial diversity in the deep soil.Meanwhile,both EIS-20 and SG effectively increased the relative abundance of Proteobacteria,Bacteroidia and Firmicutes in the surface soil,while EIS-40 and EIS-60 treatments increased the relative abundance of Gemmatimonadaceae and Nitrospira in the deep soil.In addition,Proteobacteria,Bacteroidia and Firmicutes were the main factors affecting the content of organic carbon components,cluster formation and changes in the molecular structure of organic carbon in the topsoil.Nitrospirae and Gemmatimonadetes are the main factors affecting the content of organic carbon components and molecular structure changes in the deep soil.6.SM and SG significantly increased the abundance of fungal communities in the 0-20 cm soil layer,while the EIS-40 and EIS-60 treatments had the highest fungal diversity in the 20-40 cm and 40-60 cm soil layers,respectively.At the same time,EIS also significantly increased the relative abundance of Ascomycota and Sordariomycetes in each soil layer,and SG and SM treatments also had higher relative abundance of Ascomycota,Zygomycota and Mortierella.in the0-20 cm soil layer.In addition,changes in fungal community structure of Ascomycota,Chytridiomycota and Glomeromycota could accelerate the accumulation of chemical fractions in soil organic carbon and promote the alkylation of soil organic carbon structure and the formation of microaggregates and macroaggregates in soil.In general,EIS-20 and SG are very important to improve the organic carbon pool and microbial community in the surface layer of the soil;and from the different depths of straw return,EIS-40 and EIS-60 help to promote the accumulation of deep soil organic carbon and improve soil fertility and microbial community structure,which is a more suitable mode of straw return in the black calcium soil area of northeast China.