Influence Of Nitrogen Management Practices On Soil Microbial Communities In Soybean Planting Systems

The maintenance of soil microbial diversity is critical for the sustainable development of agriculture.Different soybean cropping patterns and fertilizations can alter soil nitrogen.However,the influences of nitrogen management practices on the structures and nitrogen-cycling functions of soil microbial communities remain unknown.This study focused on soybean which is one important economic and green manure crop.We collected soil samples under different soybean cropping patterns in three representative soybean planting regions across China.Besides,rhizospheric and bulk soil samples were collected from five developmental stages of soybean,which grew in soils receiving long-term organic and inorganic nitrogen inputs.High-throughput sequencing data of microbial communities,soil property,and nitrogen-cycling function data were used to explore how the functional traits and life history strategies of bacterial,archaeal,and fungal communities respond to different soybean cropping patterns;to analyze how bacterial and fungal communities respond to soil property variations caused by long-term fertilization and their contribution to soil nitrogen cycling;to predict the key inter-phylum bacterial interactions that influence community dynamics and functions during soybean development;to analyze the assembly processes of the stage-specific absent fungal taxa and their impact on fungal community stability.The analysis results are as follows:1.Soybean and maize intercropping increased soil carbon and nitrogen pools,while soybean and gramineous crops rotation reduced soil carbon pool.By analyzing the shared species between keystones and indicators(keystone indicators),the selection of microbial communities by cropping patterns was observed at both taxonomic and functional levels.Intercropping harbored more bacterial and fewer fungal keystone indicators than rotation,which were characterized by special substrate preference in the two systems.Moreover,soil properties represented by labile carbon oppositely influenced bacterial and archaeal core functional traits,but did not significantly impact fungal core functional traits.The ecological associations between soil properties and microbial functional traits illustrated that bacterial and archaeal life history strategies were affiliated to resource acquisition,while fungi adopted high yield strategy.2.High levels of organic nitrogen significantly increased bacterial alpha diversity.Fungal alpha diversity weakly and inconsistently responded to fertilization treatments.Besides,bacterial alpha diversity was significantly higher in the rhizosphere of the wheat root that was under decomposition than in the bulk soil,while fungal richness was significantly higher in rhizosphere.Organic nitrogen application significantly increased bulk soil nutrients.However,efficient utilization of inorganic nitrogen fertilizer by plants resulted in a slight increase in bulk soil nutrients.Thus,microbial beta diversity was higher in rhizosphere than in bulk soil under inorganic treatment,while fungal beta diversity was higher in bulk soil than in rhizosphere under organic treatment.In addition,random forest analysis showed that soil properties significantly contributed to the potential nitrification,denitrification,and N₂O emission in bulk soil.And fungal beta diversity significantly contributed to the potential N₂O emission in bulk soil.Correlation analysis showed that bacterial beta diversity negatively correlated with the potential nitrification in bulk soil.3.The stages of soybean development outcompeted nitrogen fertilization management in shaping bacterial community structure,while fertilization treatments significantly shaped the abundance distribution of nitrogen functional genes.Temporal variations in bacterial abundances increased in bulk soils,especially at the stage of soybean branching,which helps to infer underlying negative interspecies interactions.Members of Cyanobacteria and Actinobacteria actively engaged in inter-phylum negative interactions in bulk soils and soybean rhizosphere,respectively.Furthermore,the negative interactions between nitrogen-fixing functional groups and the reduction of nif H gene abundances were coupled during soybean development,which may help to explain the linkages between population dynamics and functions.4.Alpha diversity analysis revealed that rhizospheric communities decreased population size during the developmental transitions of soybean.A large number of temporally missing taxa were assigned to Ascomycota and Basidiomycota.Some plant pathogens in phylum Ascomycota showed stage-specific loss in soybean rhizosphere.The remaining sub-communities and the whole communities fitted the neutral model to some extent.Their assembly processes were primarily governed by dispersal limitation in both sampling compartments,and secondly by variable selection and ecological drift in bulk soil and rhizosphere,respectively.The missing sub-communities were non-neutral and primarily dominated by drift.Moreover,both the highly-connected network nodes and the missing taxa promoted the attack robustness of fungal communities.These findings highlight that different soybean cropping patterns and long-term fertilization treatments can impact microbial structure and function by changing soil nutrients.The different life history strategies of bacterial and fungal communities and their interactions might influence their responses to environmental changes and their contribution to nitrogen-cycling functions.Moreover,this study advances our understanding of the assembly of different subsets of mycobiomes,and provides a new insight into the maintenance mechanisms of metacommunity stability.