Still, the environment selects: disentangling the Effect of Distance Decay on Soil Bacterial Communities
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Abstract
Soil bacterial communities are central to ecosystem functioning, yet the relative importance of dispersal limitation, environmental selection, and biotic interactions in shaping their spatial turnover remains unresolved. Distance–decay relationships (DDRs)—the decline in community similarity with geographic distance—are commonly observed for microbial communities, but their underlying drivers across ecologically relevant spatial scales remain unclear. We analyzed soil bacterial communities in temperate grasslands across two regions in Germany to quantify the contribution of geographic distance, soil physicochemical properties, plant community composition, and plant traits to bacterial β-diversity. Generalized linear modeling, variation partitioning, and commonality analysis revealed a clear DDR, with bacterial similarity declining by ~5% for each doubling of geographic distance. However, soil physicochemical heterogeneity accounted for over 50% of the explained variation in the bacterial DDR and nearly 30% of the total variation in community composition. Plant community composition independently explained additional variation, while plant functional traits had only marginal effects. Notably, fine-scale environmental heterogeneity within sites contributed to high turnover over short distances, indicating strong abiotic filtering even at the plot scale. Then, to further assess microbial distribution patterns, we examined the relationship between taxon abundance and spatial range. We found that rare taxa were both locally and broadly distributed, suggesting that rarity does not necessarily constrain dispersal. Dominant taxa, particularly from Proteobacteria and Firmicutes, were consistently broadly distributed, in accordance with generalist lifestyles. In contrast, we found a small, but taxonomically diverse group of highly abundant taxa which were distributed only over intermediate ranges, suggesting that dispersal limitation does not constrain dominance. Our results demonstrate that soil bacterial DDRs emerge primarily from environmental filtering and plant–soil interactions, with a secondary role for spatial separation. These findings highlight the importance of integrating spatially explicit sampling with soil and vegetation data in microbial biogeography, and shed light on the complex patterns of dispersal limitation in microbial communities.
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Soil prokaryotes play a crucial role in terrestrial ecosystems, yet the relative importance of dispersal limitation, environmental selection, and biotic interactions in shaping their assembly remains unresolved. To better understand the underlying drivers of soil prokaryotic communities in temperate grasslands, we sampled grassland transects across Germany, and examined how geographic distance, soil properties, plant community composition, and vegetation characteristics influence prokaryotic communities. We found a clear distance decay relationship (DDR): community similarity decreased by approximately 5% with each doubling of geographic distance. To disentangle the contribution of geographic distance from spatial changes in soil properties and vegetation, we combined variation partitioning and commonality analysis. Physicochemical heterogeneity in soil, which accounted for over ~30% of the total variation in prokaryotic community composition, explained more than 52% of the observed DDR and had a larger unique contribution to the DDR than geographic distance. In contrast, geographic distance alone only explained 2% of the variation in community composition. Small-scale variations in soil properties within individual sites resulted in high turnover over short distances, suggesting strong abiotic filtering at the local level. Plant community composition explained ~36% of the variation in community composition, but only 6.4% of the DDR, while vegetation characteristics had only marginal explanatory power. Finally, we found rare taxa that were either locally restricted or widespread, indicating that rarity does not always restrict dispersal. Dominant taxa, particularly from Proteobacteria and Firmicutes, were consistently widespread, aligning with generalist strategies. Interestingly, a smaller group of highly abundant taxa exhibited intermediate spatial ranges, suggesting that dominance does not arise solely from dispersal limitation. Overall, our findings indicate that environmental filtering and plant-soil interactions are the primary factors driving DDRs among soil prokaryotes, while geographic distance plays a lesser role. Our study emphasizes the importance of sampling methods that explicitly account for spatial patterns and integrate soil and vegetation data, enhancing our understanding of the intricate patterns of dispersal limitation in microbial communities.
https://doi.org/10.32942/X2DM0J
Environmental Microbiology and Microbial Ecology Life Sciences
soil microbiota, metabarcoding, spatial ecology
Published: 2025-07-06 15:11
Last Updated: 2025-11-07 19:08
CC BY Attribution 4.0 International
Data and Code Availability Statement:
R code for all analyses is available in GitHub (https://github.com/NeisseN/BEO_DDR).Raw sequences are publicly available in NCBI’s Sequence Read Archives under accession number PRJNA1284051, and processed data and corresponding metadata are available in BExIS (accession numbers 32155 and 332156, respectively; Neisse, 2025).
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English
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