Abstract
Ectomycorrhizal fungi (EcMF) are key components of temperate ecosystems, and recent studies suggest that they can also inhabit non-EcM plant roots as endophytes. We aimed to (1) provide new evidence of EcMF colonization of non-EcM hosts, (2) offer direct microscopic confirmation of such endophytism and (3) assess factors influencing colonization, including plant identity, site and potential root filtering. Using ITS2 amplicon sequencing, we characterized root fungal communities in 66 non-EcM plant species sampled across nine French sites. At two sites, we compared rhizosphere and root communities to test for a root filtering. We also investigated endophytism in Russula species at two Russula-rich sites via FISH and confocal microscopy. We found substantial but variable proportions of EcMF sequences in non-EcM roots, particularly near EcM trees, indicating that endophytism may serve as a secondary ecological niche. Although EcMF were more abundant in the rhizosphere than in roots, community composition was similar, suggesting limited root filtering. Microscopy revealed metabolically active Russula hyphae within the apoplast of two non-EcM plant species. Our results confirm a dual EcM/endophyte niche for Russula spp., echoing patterns observed in other EcMF. The ecological implications of this duality remain to be explored.
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Claims 4
Claim · model-written summary
Ectomycorrhizal fungal sequences made up substantial but variable proportions of non-EcM root communities, especially near ectomycorrhizal trees.
Verbatim
e0“We found substantial but variable proportions of EcMF sequences in non-EcM roots, particularly near EcM trees”
Claim · model-written summary
EcMF were more abundant in rhizosphere communities than root communities.
Verbatim
e0“Although EcMF were more abundant in the rhizosphere than in roots, community composition was similar”
e1“We found substantial but variable proportions of EcMF sequences in non-EcM roots, particularly near EcM trees”
Claim · model-written summary
Rhizosphere and root fungal community composition was similar.
Verbatim
e0“Although EcMF were more abundant in the rhizosphere than in roots, community composition was similar”
e1“We found substantial but variable proportions of EcMF sequences in non-EcM roots, particularly near EcM trees”
Claim · model-written summary
Microscopy found metabolically active Russula hyphae in the apoplast of two non-EcM plant species.
- Taxon
- non-EcM plant speciese0
- Outcome
- metabolically active Russula hyphae within the apoplaste0
- Value
- twoe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.

Verbatim
e0“Microscopy revealed metabolically active Russula hyphae within the apoplast of two non-EcM plant species”