The spatial variation of soil bacterial community assembly processes affects the accuracy of source tracking in ten major Chinese cities

Urban soils harbor billions of bacterial cells and millions of species.However,the distribution patterns and assembly processes of bacterial communities remain largely uncharacterized in urban soils.It is also unknown if we can use the bacteria to track soil sources to certain cities and districts.Here,Illumina MiSeq sequencing was used to survey soil bacterial communities from 529 random plots spanning 61 districts and 10 major cities in China.Over a 3,000 km range,community similarity declined with increasing geographic distance(Mantel r=0.62),and community composition was clustered by city(R^(2)=0.50).Within cities(<100 km),the aforementioned biogeographic patterns were weakened.Process analysis showed that homogenizing dispersal and dispersal limitation dominated soil bacterial assembly at small and large spatial scales,respectively.Accordingly,the probabilities of accurately tracking random soil sources to certain cities and districts were 90.0% and 66.7%,respectively.When the tested samples originated from cities that were more than 1,265 km apart,the soil sources could be identified with nearly 100% accuracy.Overall,this study demonstrates the strong distance-decay relationship and the clear geographic zoning of urban soil bacterial communities among cities.The varied importance of different community assembly processes at multiple spatial scales strongly affects the accuracy of microbial source tracking.

Drivers of microbial beta-diversity in wastewater treatment plants in China

As one of the most well-documented biogeographic patterns,the distance-decay relation-ship provides insights into the underlying mechanisms driving biodiversity distribution.Al-though wastewater treatment plants(WWTPs)are well-controlled engineered ecosystems,this pattern has been seen among microbial communities in activated sludge(AS).However,little is known about the relative importance of environmental heterogeneity and dispersal limitation in shaping AS microbial community across China;especially they are related to spatial scale and organism types.Here,we assessed the distance-decay relationship based on different spatial scales and microbial phylogenetic groups by analyzing 132 activated sludge(AS)samples across China comprising 3,379,20016S rRNA sequences.Our results in-dicated that the drivers of distance-decay pattern in China were scale-dependent.Microbial biogeographic patterns in WWTPs were mainly driven by dispersal limitation at both local and national scales.In contrast,conductivity,SRT,and pH played dominant roles in shaping AS microbial community compositions at the regional scale.Turnover rates and the drivers of beta-diversity also varied with microorganism populations.Moreover,a quantitative re-lationship between dispersal limitation ratio and AS microbial turnover rate was generated.Collectively,these results highlighted the importance of considering multiple spatial scales and micro-organism types for understanding microbial biogeography in WWTPs and pro-vided new insights into predicting variations in AS community structure in response to environmental disturbance.