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Science Areas
Environmental Transformations and Interactions

New Approach Expands Spatial Resolved Quantification of Nutrient Exchange in Plant Tissues, the Rhizosphere, and Soils

Improved mapping of root exudates and focusing of photosynthates within plant tissues. 

A graphic displays a laser dissecting a section of plant roots beneath the surface of soil. Popping up from the laser dissection area is a graphic representation of a selection of isotopes from the dissected root area.

Spatially constrained hotspots of plant-microbe interaction play an oversized role in nutrient biogeochemistry within terrestrial systems, but it is challenging to map their distribution given their focused spatial footprint. A new method enables quantitative mapping of carbon flow into these hotspots and enhances efforts at understanding their lifetime and controls on where they form. (Image courtesy of Environmental Molecular Sciences Laboratory)

The Science  

Organic carbon in soil is linked to enhanced plant growth and to improved subsurface biodiversity, and it is a potential sink for atmospheric carbon dioxide (CO2). Yet, injection of organic carbon into soil through various root processes is typically focused on small spatial regions, which can confound attempts to quantify the carbon and correlate it with various microenvironments that exist around plant roots. A multi-institutional team’s novel approach permits tracking of plant-derived organic carbon through plant tissues and into soil to enable detailed spatial mapping of organic carbon.  

The Impact 

Results of this study demonstrated the ability to harness stable isotope tracers in combination with a new analytical method to map recent photosynthate introduction into soil where it can fuel a range of microbial activities and contribute to landscape-scale carbon cycling. A multi-institutional team used laser ablation to target spatially specific sections of the sample for harvest and continuously analyzed the 13C content of particulates being ablated from the surface of plant tissue, rhizosphere, and soil samples. This is a significant advance from previous approaches that required batch analysis of samples on a one-at-a-time basis. As a result, this new method produces orders of magnitude more data per time of analysis, thereby enabling refined mapping of carbon in the sample.  


A multi-institutional team of researchers developed and demonstrated a new approach to characterize carbon isotopic distribution within plant tissues, the rhizosphere, and soil. They began by exposing switchgrass plants to 13CO2 in a laboratory setting. They leveraged a 13C tracer to selectively track photosynthetic materials as they were transferred through the plants’ vascular tissues and exuded into the rhizosphere. Then, using laser ablation at the Environmental Molecular Sciences Laboratory, a Department of Energy Office of Science user facility, they rastered over the material and continuously ablated the sample and combusted the resulting material. This sample-derived CO2 was pumped through a capillary absorption spectroscopy (CAS) fiber. Carefully balancing the vacuum strength helped the team optimize sample dwell time in the fiber to achieve suitable measurement precision before the sample exited the fiber. The improved sampling density of the team’s approach was made possible by employing the CAS isotope detector. The enhanced measurement sensitivity of CAS over conventional isotope ratio mass spectrometry was crucial to being able to run continuous analyses without needing to cryogenically trap the sample-derived CO2. This approach avoids a significant time lag and thereby increases the richness of the stable isotope data to better address carbon cycling questions in plant tissues, the rhizosphere, and soil.  


Jim Moran, Michigan State University | Pacific Northwest National Laboratory, | 

Daniel Cleary, Pacific Northwest National Laboratory,  

Tim Linley, Pacific Northwest National Laboratory,  


Portions of this work were funded through the DOE Office of Biological and Environmental Research program by the Small Business Technology Transfer program and a DOE Early Career Research Award. A portion of this research was performed at the Environmental Molecular Sciences Laboratory, a DOE Office of Science user facility sponsored by the Biological and Environmental Research program. 


D.M. Cleary, et al. “Laser ablation-capillary absorption spectroscopy: A novel approach for high throughput and increased spatial resolution measurements of δ13C in plant-soil systems.” Soil Biology and Biochemistry (2023), 187, 109208. [DOI: 10.1016/j.soilbio.2023.109208]