Still, the environment selects: disentangling the Effect of Distance Decay on Soil Bacterial Communities

Niklas Neisse, Maria Kostakou, Sophia Nicole Meyer, Anja Linstaedter, Antonis Chatzinotas, Stephanie D Jurburg 

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.