Bacterial Communities on Wheat Grown Under Long-Term Conventional Tillage and No-Till in the Pacific Northwest of the United States

Abstract

Cultural practices, such as tillage, often have widespread impacts on phytobiomes. No-till has been increasingly adopted by wheat growers in the dryland cropping areas of the inland Pacific Northwest in the United States to reduce soil erosion and decrease fuel and labor inputs, yet there are limited data on how conversion to no-till impacts plant-associated bacteria in this highly productive system. To address this knowledge gap, we evaluated bacterial communities in bulk and rhizosphere soil of wheat in two locations (Idaho and Washington) for 2 years, comparing long-term no-till plots and adjacent plots under conventional tillage. In this study, members of phylum Proteobacteria were relatively more abundant in rhizosphere soil, while Acidobacteria and Gemmatimonadetes were more abundant in bulk soil than in the rhizosphere. Bacteroidetes were more frequent under conventional than conservation tillage. In general, bacterial families were more affected by the position of the sample (rhizosphere versus bulk soil) than by tillage practices. Families generally regarded as copiotrophic (Oxalobacteriaceae, Pseudomonadaceae, and Cytophagaceae) were more abundant in rhizosphere soil than bulk in both years. On the contrary, oligotrophic families such as Gaiellaceae and those within Gemmatimonadetes were more abundant in bulk soil than in the rhizosphere. Families affected by tillage varied between the 2 years. These results suggest that bacterial communities in soil were more influenced by plant proximity (rhizosphere versus bulk soil) than by tillage practices, but that specific differences were not consistent and may vary among locations and years.