Skip to main content
SLU publication database (SLUpub)

Abstract

Tuberculate ectomycorrhizae (tubercles) are a type of mycorrhizal association, in which the fungus and root combine to form nodular structures. Diazotrophs associated with these structures could fix atmospheric N2 and contribute to N supply for plants in boreal forest ecosystems. Yet, very little is known about N2 fixation associated with tubercles. We quantified N2 fixation rates associated with tubercles of Scots pine (Pinus sylvestris) and in the surrounding soils, and identified diazotrophs associated with the tubercles. For this purpose, pine seedlings were grown in microcosms for three years and N2 fixation was measured using 15N-N2. We found that tubercles of Pinus sylvestris were formed by Suillus bovinus. The N2 fixation rate associated with the tubercles from one microcosm was particularly high (7587 ng N g-1h- 1) and was 35-fold higher than the mean rate of the other microcosms. The tubercles exhibited significantly higher N2 fixation rates than the soils. A total of 26 orders of diazotrophs, belonging to nine phyla (Actinomycetota, Bacteroidota, Bacillota, Cyanobacteria, Desulfobacterota, Euryarchaeota, Nitrospirota, Pseudomonadota and Thermodesulfobacteriota) was associated with the tubercles. In the tubercles with exceptionally high N2 fixation, Euryarchaeota and specifically Methanosarcinales dominated the diazotrophic community. In conclusion, the tubercles of Scots pine harbored active diazotrophs and exhibited high N2 fixation rates, potentially serving as a significant N source in boreal forests.

Keywords

Tuberculate ectomycorrhizae; Nitrogenase activity; Pinus sylvestris; Microcosm; Diazotrophic community; Fungal community; Boreal forest soil

Published in

Geoderma
2026, volume: 465, article number: 117643

SLU Authors

UKÄ Subject classification

Soil Science

Publication identifier

  • DOI: https://doi.org/10.1016/j.geoderma.2025.117643

Permanent link to this page (URI)

https://res.slu.se/id/publ/145368