Responses Of Farmland Mollisol Microorganisms And Arbuscular Mycorrhizal Fungal Communities To Tillage Practices

Mollisol is the most fertile soil type in nature,with good structure,loose and soft soil layer,high content of organic matter,good physical and chemical properties,high fertility and suitable for crop growth.Northeast mollisol area is one of the four black soil areas in the world and is an important base of commodity grain in China.The continuous cropping of maize makes soil hard and surface layer shallow,and its tillage management and fertilization is not scientific enough,which is one of the reasons for the decline of mollisoll fertility.Soil degradation worsened,and food production capacity and ecological security were seriously affected.Soil microorganism,as the core of element geochemical cycle,is an important maintainer,disintegrator and indicator of soil ecosystem.Therefore,more and more attention has been paid to the study of microbial community changes to explore the effects of different tillage management on th e mollisol farmland ecosystem and the regulatory mechanism.In this study,the long-term continuous cropping mollisol experimental field of corn was taken as the research object,and a total of 4 tillage treatments were set: no tillage,rotary tillage,sub soil tillage,deep tillage and 2 straw returning methods: straw no-returning to the field and straw returning to the field,which was treated three years.Take Biolog determined rhizosphere soil,farmland near the root of mollisol farmland soil nutrient,a rbuscular mycorrhizal fungi and Miseq high-throughput sequencing,the different treatment of mollisol nutrient,soil microbial biomass,microbial arbuscular mycorrhizal(AM)fungal biomass,diversity,community structure characteristics,from the perspective of soil microbial structure to explore the response mechanism of the northeast mollisol of different tillage measures,which will provide a scientific basis for selecting reasonable conservation tillage.The test results are as follows:(1)Although soil nutrients changed under different tillage methods,there was no significant difference in the contents of nutrients(except p H)between different tillage treatments.The p H value of straw returning with rotary tillage was significantly increased by 10% compa red with that without straw returning.Two-factor anova showed that tillage management and the interaction(tillage and straw returning)had a significant effect on soil p H.Soil total nitrogen content was significantly affected by the interaction between the two,while organic matter,total phosphorus,available phosphorus and available potassium were not affected by tillage and straw returning.(2)Different cultivation methods significantly affected soil microbial.Compared with no tillage and rotary tillage,soil microbial activity of subsoil tillage and deep tillage was significantly decreased.The utilization of polymers,carbohydrates,phenolic acids,carboxylic acids,amino acids and amines by soil microorganism was also significantly affected by differe nt tillage methods.The soil microbial utilization of the above six carbon sources was the highest in no tillage,and decreased significantly with the increase of tillage intensity.Straw returning only had significant effect on the utilization rate of polymer,but had no significant effect on the utilization rate of other carbon sources.In no tillage and subsoil tillage,straw returning caused the decrease of polymers utilization.In addition,besides phenolic acids and carboxylic acids,the use of other carbon source by soil microorganisms is also significantly affected by the interaction between them.Soil microbial Shannon diversity index,Simpson diversity index and Pielou evenness index were significantly affected by tillage methods and their interact ion,but straw returning had no significant effect on them.(3)Outside the root hyphae density and spore density of AM fungi were significantly affected by different tillage methods.Among them,outside the root hyphae density the of AM fungi in deep tillage was significantly higher than that of no tillage,but the spore density was significantly lower.The results of the structural equation model showed that the effect of tillage on the spore density of AM fungi was mainly direct,while the effect on outside the root hyphae density the of AM fungi was mainly indirect through soil compactness and root length.(4)Through the Miseq high-throughput sequencing,received 66 of AM fungi operational classification unit(OTU),including Glomeraceae to their advantage.At the level of AM fungi,the relative abundance of Ambisporaceae was significantly affected by different tillage methods.But Glomeraceae,Claroideoglomeraceae,Gigasporaceae and Paraglomeraceae relative abundance in the differences between the groups was not significant.Different tillage methods had significant effects on the abundance of AM fungi OTU,but little effects on the Shannon diversity index and Pielou evenness index of AM fungi.The abundance of AM fungus OTU was the lowest and significantly lower than that of no-tillage.Shannon diversity index and Pielou evenness index of no tillage were significantly lower than that of rotary tillage.Non-metric multidimensional scaling analysis showed that,compared with no tillage,deep tillage and subsoil tillage significantly changed the soil AM fungal community composition.Although biomass,diversity and community composition of AM fungi were not affected by straw returning,straw returning c aused changes in the net interspecific relationship of AM fungi.In conclusion,it is suggested that deep tillage and straw returning can be appropriately promoted in this area,which is of theoretical and practical significance for loose and activated soil,rational construction of surface layer and improvement of corn yield.