The Availability of Inorganic Nitrogen and Organic Carbon Manipulates Ectomycorrhizal Fungi-Mediated Iron Acquisition in the Forest Ecosystem
Authors:
Haihua Wang1*, Hui-Ling Liao1 ([email protected]), Kaile Zhang1, Tiffany Victor2, Jennifer Bhatnagar3, Rytas Vilgalys4, Kerrie Barry5, John Cliff6, Jeremy Bougoure6, Dehong Hu6, Sarah Leichty6, Ryan Tappero2 (PI)
Institutions:
1University of Florida; 2Brookhaven National Laboratory; 3Boston University; 4Duke University; 5DOE Joint Genome Institute; 6Pacific Northwest National Laboratory
Abstract
Ectomycorrhizal fungi (EMF) play a crucial role in aiding plant nutrition, specifically by extracting nitrogen (N) from organic compounds in soil organic matter (SOM)—a process known as N-mining. In iron deficient soils, EMF can strengthen iron (Fe) acquisition at both hypha-minerals and fungal-plant cell interfaces. However, the effect of EMF induced N-mining and SOM decomposition on Fe processing in mycorrhizal plants remains unclear. Furthermore, researchers aim to explore the interactive effects of inorganic N fertilization and SOM on shaping EMF-mediated Fe processes and plant Fe uptake, a topic that remains largely unexplored.
To address these questions, the team performed a mesocosm study using the Pinus-Suillus model system. Specifically, researchers inoculated Pinus taeda with Suillus cothurnatus and grew them in conditions treated with +/- Fe-coated sand, +/- SOM, and a gradient of ammonium nitrate concentrations. Using the synchrotron pink beam X-ray microfluorescence imaging (PB-XRF) on cross-sections of ectomycorrhizal roots two months post-fungal inoculation, the team found that the effect of inorganic N availability on Fe acquisition in ectomycorrhiza largely depended on SOM supply. Among the combinations of SOM and inorganic N treatments, mycorrhization demonstrated a greatest preference for +SOM/-inorganic N conditions, while mostly exhibiting negative responses to +SOM/high inorganic N conditions. With the addition of SOM, the Fe concentration in mycorrhizae was significantly decreased with the rising levels of treated inorganic N. Conversely, in the absence of SOM, an opposite trend was observed. Spatial analysis of Fe across ectomycorrhizal compartments showed that Fe was primarily accumulated in the fungal mantle underlying the Fe-enriched condition, while Fe was transferred more to the inner compartments, specifically the cortex and vascular tissues, when less Fe was acquired. These findings imply that in EMF-predominant forests, EMF may possess the capacity to facilitate Fe-associated SOM processing and mycorrhizal N/Fe uptake, enhancing the formation of mycorrhization. However, this ability may be compromised under elevated inorganic N conditions. Further studies on the molecular and biochemical aspects of plant-EMF interactions are necessary to precisely evaluate this implication. The team’s ongoing studies are dedicated to conducting these aspects of the research. For example, group members are utilizing the NanoSIMS tool to visualize and quantify the flux of N transformed from N-labeled SOM to EMF hyphae. The team also employs metatranscriptomics and fluorescence in situ hybridization imaging to visualize the activity of fungal genes responsible for cellulose metabolism in mycorrhizae, influenced by the combinations of SOM and inorganic N addition.