Responses Of Soil Bacterial,fungal And Gene Of Amo A And NirS Communities To Tillage Practices In BlackFarmland

Black soil is a precious soil resource,famous for its high organic matter and good fertility,and has long borne the heavy responsibility of food security in China.However,under the influence of highly intensive agricultural management methods,such as single tillage method,continuous cropping of maize,straw burning,and excessive application of chemical fertilizer,the structure of surface black soil becomes worse and the soil becomes hardened,which limits the stable and high yield of crops.Tillage is an important management measure that affects the properties of soil surface layer.Reasonable structure of soil surface layer plays an important role in improving soil physical and chemical properties,enhancing soil microbial function and increasing crop yield.In this study the twins cultivation experiments as the research platform,for black soil farmland of the tested soil,set up three tillage treatment: no-tillage(NT),rotary tillage(RT),the commune(DT),each processing including straw returning not(-R),straw returned(+ R),straw returned with organic fertilizer(+ RM)returning three way,trial began in 2015 after the autumn harvest.Through two consecutive years(2017-2018)of tracking and monitoring,the effects of different tillage and straw returning methods on soil fungi,bacteria,ammonia-oxidizing bacteria(AOB)and nirS type denitrifying bacteria were studied,so as to provide a scientific basis for establishing a good black soil ecosystem and surface layer structure,and maintaining a high level of productivity.The test results are as follows:(1)With the increase of cultivation years,the content of soil available nutrients increased.Notillage increased soil compactness and organic matter content and decreased pH.Soil ammonium nitrogen content decreased after straw was returned to the field.(2)In 2017(the second year of the experiment),different tillage methods had no significant effects on soil bacterial and fungal community composition,while in 2018(the third year of the experiment),different tillage methods had significant effects on soil bacterial and fungal community composition.Straw returning only caused the change of the fungal community in 2018,and had no significant effect on the bacterial community in the two years.Tillage methods indirectly affect bacterial community composition by changing soil pH,and indirectly affect soil fungal community by changing soil nutrients.(3)In 2018,the diversity of soil fungal OTU treated by DT was significantly higher than that treated by NT.Compared with NT,RT and DT treatments in 2017 and 2018 significantly increased the complexity and connectivity of bacterial co-occurrence network,and simplified the fungal network.Straw returning had no significant effect on the network parameters of bacteria and fungi in 2017,while the network complexity of bacteria and fungi decreased in 2018.(4)Soil denitrification potential and the diversity of AOB and nirS denitrifying bacteria had a positive response to straw returning,but not to tillage;Soil nitrification potential responds to tillage practices(2018).The soil nitrification potential of RT was significantly higher than that of DT.The denitrification potential was not affected by tillage method,and the soil denitrification potential was increased by 21.3% by straw returning.The diversity of AOB and nirS-type denitrifying bacteria was not significantly affected by tillage methods.Two treatments of straw returning(+R and +RM)significantly increased the diversity and community composition of AOB and nirS-type denitrifying bacteria.Soil pH and available nitrogen are the important factors affecting the community composition differentiation of AOB and nirS type denitrifying bacteria.(5)The deterministic process became the main process for the community construction of AOB and nirS-type denitrifying bacteria.DT treatment increased the proportion of random process in the community construction of nirS-type denitrifying bacteria,but had no significant effect on the community construction process of AOB.Straws returning to the field increased the complexity of AOB and nirS denitrifying bacteria networks,while DT simplified their co-occurrence networks.In conclusion,with the increase of tillage years,the effects of tillage methods on bacterial and fungal communities gradually increased.Compared with straw returning,tillage methods had more significant effects on soil bacterial and fungal communities.The effects of tillage methods on the community composition and co-occurrence network of bacteria and fungi were different.Soil AOB and nirS denitrifying bacteria communities and their network structure were affected by tillage and returning methods.