Tracing rhizosphere carbon exchange processes and nutrient interactions
EMSL Project ID
51693
Abstract
Rhizodeposition represents the largest flux of photosynthetically derived organic matter into soil for most terrestrial systems and, in so doing, serves as a major point of connection between atmospheric and soil systems. Yet, the constrained spatial confines, complex geochemistry, temporal transience, and highly diverse and active microbial populations characteristic of rhizosphere systems complicate efforts to effectively evaluate nutrient dynamics and the drivers by which the tripartite plant-microbial-geochemical interactions ultimately govern carbon fate, plant productivity and resilience, and overall ecosystem health. We propose a series of techniques that will allow this team, as well as future EMSL users, advanced analytical access to the dynamic rhizosphere. These approaches will provide needed resolution to enable interpretation of results within the context of specific microenvironments of rhizosphere systems. We will enable: 1) highly quantified, taxonomic tracking of 13C labeled root exudate uptake into targeted microbial groups, 2) non-destructive, spatially resolved proteomics coupled to 13C tracers, and 3) intramolecular stable isotope analysis of a C-rich root exudate. Developing taxon-specific quantification of delta-13C will leverage direct measurement of RNA by isotope ratio mass spectrometry (IRMS). We seek to develop a specific enzymatic approach to cleave small subunit rRNA where the resulting ('cut') fragments will be separated by liquid chromatography then selectively analyzed for delta-13C using liquid chromatography-IRMS. This approach can selectively be targeted to broad or narrow taxonomic groups (domain to genus level specificity is possible) and quantify differential C shuttling from root exudates to specific microbial components of the system (various plant growth promoting organisms, fungal groups, etc.) and how these interactions are modified in response to nutrient perturbations in the system. The resulting level of quantification of C exchange to specific taxonomic groups is not approachable with currently available, sequencing based techniques. Spatially resolved proteomic measurements will leverage a membrane blotting technique to extract proteins from soil while retaining their 2D spatial orientation. We will improve sample preparation approaches to permit fine-scale resolution, with up to 1mm resolution expected. Given the nature of protein extraction for this method, the approach is non-destructive and can support timeseries sampling to track changes in the spatial proteome over time, the impact of various environmental perturbations, or microbial community succession patterns. Finally, we seek to leverage advanced mass spectrometry capabilities at EMSL to quantify position-specific shifts in isotope content at distinct bonds within organic molecules. We anticipate that microbial degradation processes will induce isotopic fractionation at the site of enzymatic attach. Advanced position-specific stable isotope analysis can therefore provide information on the history of soil organic molecules and indicate the degree to which specific molecules are being degraded in soils. We will use phosphatidylcholine as a target molecule to both develop needed isotopic measurement approaches and provide preliminary evaluation of changes in position-specific isotope content resulting from microbial degradation. Together, we anticipate that the capabilities being developed in this project could support wide ranging efforts to better understand the biogeochemistry of complex, dynamic rhizosphere systems.
Project Details
Start Date
2020-10-26
End Date
2023-11-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members