Spatial dominance over temporal dynamics in urban soil bacterial communities and its implications for forensic geolocation

Abstract

Soil microbial communities represent high-resolution environmental fingerprints with considerable potential for forensic microbial geolocation. However, spatiotemporal variation patterns, carrier substrate effects, and interannual dynamics of soil microbes in urban environments remain poorly understood. Here, we conducted a 393-day systematic survey encompassing 16 sampling time points at six representative sites across three major Chinese cities (Beijing, Nanjing, and Guangzhou). By comparing bacterial communities associated with in situ soil, tool soil, and shoe-sole soil, we assessed the forensic geolocation potential of different soil carriers. Spatial factors explained a substantially greater proportion ofvariation in soil bacterial community composition (13.4%) than temporal factors (2.3%). Community similarity exhibited a distance–decay relationship that was more than 28 times (R²) stronger along geographic distance than along temporal distance, with significant but weak temporal distance–decay detected only when absolute time intervals were considered. Bacterial communities associated with tool soil closely resembled those of in situ soil and retained a comparable spatial distance–decay pattern. In addition, community composition showed no significant cyclical recurrence at interannual scales, as seasonal fluctuations far exceeded interannual variation. Collectively, these results demonstrate that urban soil bacterial communities maintain strong and stable spatial differentiation that is largely independent of interannual cyclicity. Importantly, tool soil effectively preserves the spatial microbial signature of in situ soil, indicating that it constitutes a more reliable forensic carrier than shoe-sole soil. Our findings provide a robust ecological foundation for the application of microbial evidence in forensic geolocation.

Graphical abstract

Keywords

soil bacterial communities / spatiotemporal variation / distance-decay relationship / temporal dynamics / forensic microbial geolocation / soil carrier effects

Highlight

	● Spatial factors dominate urban soil bacterial community variation over time.
	● Soil microbiomes show no predictable cyclical interannual recurrence.
	● Tool soil retains geographic microbial signatures better than shoe-sole soil.

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