Towards an Integrated Understanding of Soil-Microbe-Fungi Interactions in the Rhizosphere using Novel Sample Approaches and Synchrotron X-ray Fluorescence Imaging

The Structural Molecular Biology Resource at the Stanford Synchrotron Radiation Lightsource (SSRL), a BER funded user facility, has several µ-X-ray Fluorescence (µ-XRF) imaging beamlines that combine µ-XRF imaging and X-ray Absorption Near Edge Structure (XANES) spectroscopy to generate chemical speciation maps, catering to a wide variety of samples and science needs. The SSRL µ-XRF imaging beamlines are well-suited for characterizing the chemistry of important biologically relevant elements (from Phosphorus through most of the periodic table) across a range of spatial scales, with x-ray spot sizes from 0.5 to 250 µm and sample size accommodations from 100's µm up to 300 x 600 mm. Recent efforts to expand the number of user groups in biological and environmental science at these beamlines has encouraged a breadth of unique samples and novel hypotheses, particularly from rhizosphere studies. We have generated new and exciting data that contribute to furthering our understanding of a number of rhizosphere processes, including; (1) the role of fungal hyphae in the uptake and transport of nutrients from soil minerals, (2) Fe redox chemistry between soil minerals, microbes and lignin, (3) soil microenvironments as locations for enhanced microbial decomposition of organic matter, and (4) plant directed root exudation towards microenvironmental hotspots for phosphorus acquisition. In each case, we adapted the unique experiments and sample environments to suit both synchrotron and supporting analyses such as field/in-situ observations, SIMS, proteomics, cryo-TEM, mössbauer spectroscopy, enzyme zymography, x-ray CT and LA-IRMS. Such an approach allows direct correlation between spatial variability in the chemistry of biologically relevant elements (K, Fe, Mn, P) with fungi activity, microbial function, physical processes and carbon cycling. These individual projects not only work towards understanding small-scale rhizosphere processes, but come together to advance a more complete understanding of the breakdown, transport and utilization of nutrients between the subsurface rhizosphere and overlying ecosystem.