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Fungal heart-rot communities of British oak (Quercus spp.) trees

Wright, Richard 2023. Fungal heart-rot communities of British oak (Quercus spp.) trees. PhD Thesis, Cardiff University.
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Oaks support the most biodiversity of any native British tree species and play vital roles in mitigating climate instability. The UK hosts a globally important population of veteran and ancient oak trees, more than the whole of Europe combined. The heart-rot of oak tree trunks provides abundant micro-habitats for a vast range of species and can be observed in some of the youngest to the most wizened ancient trees. Little is known about the fungal communities that engineer the deadwood habitats in these keystone trees. This thesis sheds light on this community, its diversity, succession, and the abiotic factors, particular to oak heartwood, that shape it. Sporocarp observations and wood sampling methods were used to examine the fungal community composition in the trunk heartwood of British oak trees. Throughout all investigations, two keystone decay species, Fistulina hepatica and Laetiporus sulphureus were consistently dominant, with only one other species, Grifola frondosa being detected causing primary heart-rot. 67 % of the oak trees sampled had one or more basidiomycete wood decay species present the dominant keystone species, Fistulina hepatica, occurred in 27 % of trees, covering 22.2 % of the entire volume of wood sampled. A complex community of 176 saproxylic species of fungi were detected by culturing methods, and it was found that the presence of Fistulina hepatica was significantly associated with 34 % of species richness, demonstrating its keystone status. Fungal community composition significantly varied between sites, though a core group of species was found to be shared between them all. The three-dimensional extents of fungal territories and the visual indications of their presence were explored through whole trunk transverse slice sampling experiments, revealing mycelia of multiple keystone species’ genotypes, that extended throughout the whole height of oak trunks. The abundant presence of tannins in oak heartwood was found to be a significant abiotic factor in shaping the fungal community, influencing the distribution of fungi throughout the tree and tipping the balance in the outcomes of fungal interactions. The variation in the ability of key oak associated fungi to deploy tannin degrading enzymes (tannases) is demonstrated through ecophysiology experiments, examining growth, decay rate, and tannase production, and is used to define their roles in heart-rot, or their absence in heartwood tissues. Interaction experiments in oak wood blocks and artificial media containing tannins were used to assess combative ability of key oak associated fungi, elucidating the hierarchical structure of the fungal community in heartwood. Fistulina hepatica was found to be the most combative, demonstrating its dominance in oak is due to more than just stress tolerance. Ascomycetes were found to be poor combatants against basidiomycete species, vii though some species were more successful on tannin containing media. Deadlocks were very common in oak wood and tannin media interactions, indicating the probable long standing coexistence of decay species in oak heartwood, at least in the primary stages of decay.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Biosciences
Subjects: Q Science > Q Science (General)
Date of First Compliant Deposit: 30 January 2024
Last Modified: 31 Jan 2024 14:09

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