|Lippold, E; Schlüter, S; Mueller, CW; Höschen, C; (...), ; Lehndorff, E: Correlative Imaging of the Rhizosphere ─ A Multimethod Workflow for Targeted Mapping of Chemical Gradients, Environmental Science & Technology, 57(3), 1538-1549 (2023), doi:10.1021/acs.est.2c07340|
ABSTRACT: Examining in situ processes in the soil rhizosphere requires spatial information on physical and chemical properties under undisturbed conditions. We developed a correlative imaging workflow for targeted sampling of roots in their three-dimensional (3D) context and assessed the imprint of roots on chemical properties of the root−soil contact zone at micrometer to millimeter scale. Maize (Zea mays) was grown in 15N-labeled soil columns and pulse-labeled with 13CO2 to visualize the spatial distribution of carbon inputs and nitrogen uptake together with the redistribution of other elements. Soil columns were scanned by Xray computed tomography (X-ray CT) at low resolution (45 μm) to enable image-guided subsampling of specific root segments. Resin-embedded subsamples were then analyzed by X-ray CT at high resolution (10 μm) for their 3D structure and chemical gradients around roots using micro-X-ray fluorescence spectroscopy (μXRF), nanoscale secondary ion mass spectrometry (NanoSIMS), and laser-ablation isotope ratio mass spectrometry (LA-IRMS). Concentration gradients, particularly of calcium and sulfur, with different spatial extents could be identified by μXRF. NanoSIMS and LA-IRMS detected the release of 13C into soil up to a distance of 100 μm from the root surface, whereas 15N accumulated preferentially in the root cells. We conclude that combining targeted sampling of the soil−root system and correlative microscopy opens new avenues for unraveling rhizosphere processes in situ. KEYWORDS: X-ray computed tomography, micro-X-ray fluorescence spectroscopy, nanoscale secondary ion mass spectrometry, laser-ablation isotope ratio mass spectrometry, distance maps, 2D−3D registration, Zea mays L.