Distinct Ecological Mechanisms Drive The Spatial Scaling Of Abundant And Rare Microbial Taxa In A Coastal Sediment

Microbes are ubiquitous in the Earth’s biosphere,executing essential ecosystem functions and maintaining ecosystem stability.Unraveling the ecological mechanisms that drive the patterns of microbial communities across space and time is an essential issue in microbial biogeography.This study links microbial spatial scaling with ecological mechanisms and aiming to provide novel mechanistic insights into the biogeographic patterns followed by different types of microbes.The Beibu Gulf region in the northwest of the South China Sea was selected as our study area,which is a semi-enclosed,typical subtropical Marine bay.A total of 29 sediment samples were collected across Beibu Gulf.Two typical spatial scaling models,including the diversity-area relationship(DAR)and the distance-decay relationship(DDR),were investigated using high-throughput sequencing techniques.To overpass the ambiguous definition of abundant and area taxa in microbial ecology,the α-and β-diversity indices were extended to Hill number.The contribution of abundant and rare microbial taxa on DAR and DDR was verified by increasing the diversity order q,i.e.decreasing the weight on rare microbial taxa.Null model analysis,which quantifies the contribution of different ecological processes to the construction of microbial communities,was used to explore the relationship between local community assembly mechanisms and spatial scale patterns of microorganisms.As a result,both environmental heterogeneity and community assembly mechanism were responsible for the differences in microbial spatial scale patterns.Strong spatial scaling patterns were observed for the whole community and rare subcommunities.In contrast,only weak patterns were observed for abundant subcommunities.The strong contribution of rare taxa to microbial spatial scaling was further confirmed by extending the spatial scale diversity indices(DAR and DDR)to Hill numbers.Furthermore,strong ecological drift and dispersal limitation underlay the strong spatial scaling patterns of rare subcommunities,whereas a high degree of homogeneous selection weakens the spatial scaling of abundant subcommunities.Such differed contribution of homogeneous selection and dispersal limitation exhibited by abundant and rare subcommunities was also verified by a deep sequencing experiment.The results demonstrated that rare taxa were responsible for the spatial scaling patterns of sediment microbial communities in the Beibu Gulf.Different ecological mechanisms mediated the different biogeographic patterns of abundant and rare taxa.This study provided novel insight into the spatial scaling followed by different types of microorganisms.