BayCEER Workshop 2025

Carbon allocation in the plant-soil-fungal system: real-time non-invasive 3D visualization and quantification with radioactive Carbon-11

Plant symbioses with mycorrhizal fungi facilitate substantial carbon (C) fluxes from plants to soils and thus contribute to terrestrial C stocks. The visualization and quantification of C fluxes in the plant and fungal mycelium with radioactive ¹⁴C tracer have greatly enhanced our understanding of assimilate allocation patterns related to mycorrhizal symbiosis. Now, the ¹¹C tracer in combination with Positron Emission Tomography (PET) adds another dimension: 3D imagery with a high temporal resolution.
To investigate short-term C fluxes in the plant-soil system as a function of mycorrhizal colonization intensity, we studied the rate of assimilate transport from above- to belowground plant compartments of ectomycorrhizal trees. For this, we planted ten one-year old Fagus sylvatica trees in pots with forest topsoil. In order to investigate the C investment of the trees into phosphorus supply by mycorrhizae, each pot contained an ingrowth core with apatite-enriched forest topsoil. The ingrowth core is covered with a 30 µm mesh only allowing hyphal ingrowth, thus increasing the need of C investment by the tree into the fungal mycelium.  We successfully used Magnetic Resonance Imaging (MRI) to generate belowground 3D images of tree root architecture and additionally combined ¹¹CO₂ pulse labelling with PET to visualize, in 3D and in vivo, the flow of C assimilates from tree leaves to the soil. Combined, MRI and PET is a non-invasive approach that provides real-time visualization of C allocation in the plant-soil system and allows to quantify assimilates translocation speed in the plant phloem as a function of the C sink strength of the mycorrhizal fungi under changing growth conditions.