Soil depth and geographic distance modulate bacterial beta-diversity in deep soil profiles throughout the US Corn Belt

Understanding how microbial communities are shaped across spatial dimensions is of fundamental importance in microbial ecology. However, most studies on soil biogeography have focused on the topsoil microbiome, while the factors driving the subsoil microbiome distribution are largely unknown. Here we used 16S rRNA amplicon sequencing to analyse the factors underlying the bacterial beta-diversity along vertical (0-240 cm of soil depth) and horizontal spatial dimensions similar to 500,000 km(2)) in the U.S. Corn Belt. With these data we tested whether the horizontal or vertical spatial variation had stronger impacts on the taxonomic (Bray-Curtis) and phylogenetic (weighted Unifrac) beta-diversity. Additionally, we assessed whether the distance-decay (horizontal dimension) was greater in the topsoil (0-30 cm) or subsoil (in each 30 cm layer from 30-240 cm) using Mantel tests. The influence of geographic distance versus edaphic variables on the bacterial communities from the different soil layers was also compared. Results indicated that the phylogenetic beta-diversity was impacted more by soil depth, while the taxonomic beta-diversity changed more between geographic locations. The distance-decay was lower in the topsoil than in all subsoil layers analysed. Moreover, some subsoil layers were influenced more by geographic distance than any edaphic variable, including pH. Although different factors affected the topsoil and subsoil biogeography, niche-based models explained the community assembly of all soil layers. This comprehensive study contributed to elucidating important aspects of soil bacterial biogeography including the major impact of soil depth on the phylogenetic beta-diversity, and the greater influence of geographic distance on subsoil than on topsoil bacterial communities in agroecosystems.

Automated summary

This study analyzed the bacterial diversity in soil samples from the U.S. Corn Belt using 16S rRNA sequencing. The results showed that soil depth had a major impact on the phylogenetic diversity of bacteria, while geographic location had a greater influence on the taxonomic diversity. The study also found that the distance-decay effect was stronger in the subsoil layers compared to the topsoil. Overall, this comprehensive study provides insights into important aspects of soil bacterial biogeography.