title: Competition between plant and bacterial cells at the microscale regulates the dynamics of nitrogen acquisition in wheat (Triticum aestivum).
abstract: 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 (NanoSIMS-SII), we quantified the fate of ¹⁵N over both space and time within the rhizosphere. We pulse-labelled the soil surrounding wheat (Triticum aestivum) roots with either ¹⁵NH₄⁺ or ¹⁵N-glutamate and traced the movement of ¹⁵N over 24 h. Imaging revealed that glutamate was rapidly depleted from the rhizosphere and that most ¹⁵N was captured by rhizobacteria, leading to very high ¹⁵N microbial enrichment. After microbial capture, approximately half of the ¹⁵N-glutamate was rapidly mineralized, leading to the excretion of NH₄⁺, which became available for plant capture. Roots proved to be poor competitors for ¹⁵N-glutamate and took up N mainly as ¹⁵NH₄⁺. Spatial mapping of ¹⁵N revealed differential patterns of ¹⁵N uptake within bacteria and the rapid uptake and redistribution of ¹⁵N 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.
authors.affiliation: Environment Centre Wales, Bangor University, Gwynedd, LL57 2UW, UK.
authors.forename: David L
authors.initials: DL
authors.lastname: Jones
authors.affiliation: Centre for Microscopy, Characterisation and Analysis, University of Western Australia, Crawley, WA, 6009, Australia.
authors.forename: Peta L
authors.initials: PL
authors.lastname: Clode
authors.affiliation: Centre for Microscopy, Characterisation and Analysis, University of Western Australia, Crawley, WA, 6009, Australia.
authors.forename: Matt R
authors.initials: MR
authors.lastname: Kilburn
authors.affiliation: School of Agriculture, Food and Rural Development, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Stockdale
authors.affiliation: Soil Biology and Molecular Ecology Group, School of Earth and Environment, Institute of Agriculture, University of Western Australia, Crawley, WA, 6009, Australia.
authors.forename: Daniel V
authors.initials: DV
authors.lastname: Murphy
mesh_terms: D064751:Ammonium Compounds / Q000378:metabolism; D001419:Bacteria / Q000378:metabolism*; D018698:Glutamic Acid / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D009587:Nitrogen Isotopes / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism*; D058441:Rhizosphere; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D014908:Triticum / Q000378:metabolism*
chemical_list: D064751:Ammonium Compounds; D009587:Nitrogen Isotopes; D012987:Soil; D018698:Glutamic Acid; D009584:Nitrogen
keywords: NanoSIMS; amino acids; dissolved organic nitrogen; nitrogen cycling; nutrient uptake; rhizobacteria; rhizosphere architecture