Abstract
Background and aims
Ectomycorrhizal fungi synthesize carbohydrates and amino acids from recent photosynthate but can also assimilate soil-derived amino acids. The dynamics of different amino acid pools within fungi may differ because of differences in biosynthetic complexity and energetics.
Methods
To study carbon dynamics between Pinus sylvestris and ectomycorrhizal fungi, 13CO2 pulses were traced for 97 days post-labeling into amino acids and structural carbon of Cortinarius semisanguineus and Lactarius rufus sporocarps.
Results
Without 13C labeling, amino acid δ13C was higher in Cortinarius than Lactarius, which suggested uptake of older, soil-derived amino acids by Cortinarius. In stepwise regression, 13C labeling in amino acids was 59 ± 2% of that in structural carbon. This first amino acid pool derived from recent plant sugars and peaked 16 days after 13CO2 labeling. The other 41% of amino acid carbon peaked on day 30, at 23% of the 13C enrichment of structural carbon, indicating two amino acid pools differing in 13C dynamics.
Conclusion
I hypothesized that amino acids derived from recent plant sugars mostly had simple synthesis pathways (such as alanine, aspartic acid and glutamine), whereas the second pool reflected soil-derived or slow-turnover amino acids (such as lysine, leucine, and isoleucine) with multiple enzymatic steps to synthesis. Studies of amino acid use by ectomycorrhizal fungi should account for differences in dynamics and energetic costs between these two groups of amino acids.
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Data availability
The data analyzed in the current study are available as Supplementary Table S1.
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Acknowledgements
This work was supported by U.S. National Science Foundation grants DEB-0743348 and OPP-0612598. I thank Mona Högberg for supplying sporocarp samples, Andy Ouimette and Zach McEvoy for laboratory assistance, and Rebecca Hood-Nowotny, Thomas Larsen, Katja Rinne-Garmston, Wolfgang Wanek, Andy Ouimette, John Hobbie, and three anonymous reviewers for comments on the manuscript.
Funding
This work was supported by U.S. National Science Foundation grants DEB-0743348 and OPP-0612598.
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Hobbie, E.A. 13C pulse labeling indicates differing dynamics for two pools of amino acids in ectomycorrhizal fungi. Plant Soil 491, 457–466 (2023). https://doi.org/10.1007/s11104-023-06125-0
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DOI: https://doi.org/10.1007/s11104-023-06125-0