Soil acidification modifies soil depth-microbiome relationships in a no-till wheat cropping system

Soil pH is among the most important drivers of soil bacterial community composition and diversity. However, most studies exploring the spatial distribution of soil bacterial communities have focused on the top 10–20 cm of soil, leaving our knowledge of the composition, diversity, and forces structuring subsoil communities relatively unexplored. Moreover, in agricultural soil managed without tillage (no-till), fertilizers often generate an acidified soil layer in the seed zone, rendering no-till soils a unique system in which to study the relative impacts of pH and soil depth on microbial communities. We characterize the composition and diversity of bacterial communities in a no-till wheat-based cropping system from eastern Washington, across soil depths (0 cm, 10 cm, 25 cm, 50 cm, 75 cm, and 100 cm). Soil depth was a strong driver of bacterial community composition and diversity. Proteobacteria and Actinobacteria dominated the soil surface, Acidobacteria peaked in relative abundance at 10 cm, and Actinobacteria and unidentified taxa were greatest in relative abundance below 25 cm. However, acidified soil disrupted relationships between soil depth and bacterial communities, resulting in a low diversity and distinct composition of bacterial communities at the 10 cm depth. Co-occurrence networks of bacterial taxa revealed groups of co-occurring taxa that responded primarily to soil pH or depth. This work provides an insight on the distribution and drivers of bacterial communities in deep soil profiles in dryland wheat-based cropping systems.