Importance of spatially structured environmental heterogeneity in controlling microbial community composition at small spatial scales in an agricultural field

Spatial heterogeneity is an inherent feature of soils that has significant functional implications, particularly when the activities of soil microbial communities are considered. The main goal of this study was to determine the physical–chemical properties best correlated with changes in microbial community composition in an agricultural ecosystem, as part of an effort to better understand what environmental factors control the distribution and organization of soil microbes. In addition, we sought to determine: (i) whether these factors vary depending on the spatial extent considered, and (ii) whether different subsets of the microbial community were linked with different environmental variables. This analysis was conducted in a spatially explicit manner via a series of Mantel and partial Mantel tests to examine the relationship between the microbial community and the soil microenvironment while controlling for any shared spatial structure. Two-hundred soil samples were collected with separation distances ranging from 2.5 cm to 11 m, and the multi-scale spatial distributions of soil carbon (C), nitrogen (N), organic matter (OM), texture, and bacterial abundance were compared with previously published analyses of microbial community structure. The results of the spatial analysis of soil properties were similar to those obtained for the microbial communities, and considerable spatial structure was detected, even at very small scales (i.e., ≤40 cm). A strong link between the microbial community and the soil physical–chemical properties was established, and different subsets of the microbial community responded differently to the various environmental properties. C and N affected the widest portion of the microbial community, while patterns in OM distribution and soil texture were selectively correlated with specific groups of microbes. Collectively, these results demonstrate the value of considering multiple spatial scales when studying community–environment interactions, and that one's interpretation of these relationships is critically dependent on the scale of the investigation and the aspect of the community considered. Understanding how microbial communities develop and organize will help scientists interpret the interplay of dispersal, disturbance, and local dynamics in spatial mosaics, and may have important implications for land management following natural disturbances or human alterations.