Root and microbial contributions to anoxic microsite formation in the rhizosphere: a microfluidic approach

Plant root-associated anoxic microsites may influence the fate of nutrients and contaminants in the rhizosphere, but their dynamics remain relatively unknown. To examine the formation of root-induced anoxic microsites over space and time, we use microfluidic devices integrated with transparent, planar oxygen sensors in a wheat (Triticum aestivum) rhizosphere, with and without soil microorganisms. We found that suboxic (< 2% air saturation) conditions commonly establish at root tips and more rarely establish along more mature root segments, particularly in the presence of soil organic matter and complex microbial communities. Additionally, the distribution of oxygen, and thus root-induced anoxic microsites, depends on complex interactions among light-dark cycles, growth rate, and presence of microorganisms in the rhizosphere. This study provides real-time observations of the micron-scale oxygen dynamics around actively growing roots, thereby linking root physiology to anoxic microsite formation in the rhizosphere. Our work suggests a strong potential for root-driven anoxic microsite formation, prompting important questions about anoxic microsite impact on biogeochemical processes in natural rhizosphere soil.