In Situ Mapping of Nutrient Uptake in the Rhizosphere Using Nanoscale Secondary Ion Mass Spectrometry

Abstract

Plant roots and microorganisms interact and compete for nutrients within the rhizosphere, which is considered one of the most biologically complex systems on Earth. Unraveling the nitrogen (N) cycle is key to understanding and managing nutrient flows in terrestrial ecosystems, yet to date it has proved impossible to analyze and image N transfer in situ within such a complex system at a scale relevant to soil-microbe-plant interactions. Linking the physical heterogeneity of soil to biological processes marks a current frontier in plant and soil sciences. Here we present a new and widely applicable approach that allows imaging of the spatial and temporal dynamics of the stable isotope 15 N assimilated within the rhizosphere. This approach allows visualization and measurement of nutrient resource capture between competing plant cells and microorganisms. For confirmation we show the correlative use of nanoscale secondary ion mass spectrometry, and transmission electron microscopy, to image differential partitioning of 15 NH 4 + between plant roots and native soil microbial communities at the submicron scale. It is shown that 15 N compounds can be detected and imaged in situ in individual microorganisms in the soil matrix and intracellularly within the root. Nanoscale secondary ion mass spectrometry has potential to allow the study of assimilatory processes at the submicron level in a wide range of applications involving plants, microorganisms, and animals.

Progress and challenges in using stable isotopes to trace plant carbon and water relations across scales

“…Although adequate sample preparation remains challenging, imaging mass spectrometry via NanoSIMS represents a promising avenue for mapping the spatial organisation, metabolic pathways and resource fluxes within cells, plants and at the root-fungus-soil interface, in particular in labelling studies (e.g. Clode et al, 2009). …”

Application of nanoscale secondary ion mass spectrometry to plant cell research

“…1C and D). 8 It was shown that introduced 15 N could be detected, and more importantly, mapped, in individual bacterial cells found in the soil matrix, within the rhizosphere, within root hairs, and intra-cellular within the root. 15 n/ 14 n ratio image from nanoSimS of the same bacteria.…”

Challenges in imaging and predictive modeling of rhizosphere processes

“…Internal structures of the root were visible, as well as the chemical composition of the minerals at the root surface. Further examples for NanoSIMS, a similar technique with much higher resolution, can be found in Clode et al (2009). While ToFSIMS is able to identify the entire atomic mass range in a single run, NanoSIMS requires that masses of interest be selected prior to the measurement.…”