Competition between plant and bacterial cells at the microscale regulates the dynamics of nitrogen acquisition in wheat (<i>Triticum aestivum</i>)

Summary The ability of plants to compete effectively for nitrogen (N) resources is critical to plant survival. However, controversy surrounds the importance of organic and inorganic sources of N in plant nutrition because of our poor ability to visualize and understand processes happening at the root–microbial–soil interface. Using high‐resolution nano‐scale secondary ion mass spectrometry stable isotope imaging (Nano SIMS ‐ SII ), we quantified the fate of 15 N over both space and time within the rhizosphere. We pulse‐labelled the soil surrounding wheat ( Triticum aestivum ) roots with either or 15 N‐glutamate and traced the movement of 15 N over 24 h. Imaging revealed that glutamate was rapidly depleted from the rhizosphere and that most 15 N was captured by rhizobacteria, leading to very high 15 N microbial enrichment. After microbial capture, approximately half of the 15 N‐glutamate was rapidly mineralized, leading to the excretion of , which became available for plant capture. Roots proved to be poor competitors for 15 N‐glutamate and took up N mainly as . Spatial mapping of 15 N revealed differential patterns of 15 N uptake within bacteria and the rapid uptake and redistribution of 15 N within roots. In conclusion, we demonstrate the rapid cycling and transformation of N at the soil–root interface and that wheat capture of organic N is low in comparison to inorganic N under the conditions tested.