title: Evaluating the impact of tree provenance, tree phenotype and emergent disease on microbial and insect populations in tree ecosystems
Creators: name: Roy, Shyamali Rebecca
Publisher: name: University of Reading
Year: 2020

description: Trees host complex microhabitats, supporting a wide diversity of organisms. This study focuses on two of these communities: the insect herbivores and the microbial endophytes. Studies in the field of community genetics have demonstrated that intraspecific genetic variation in a foundation species can have cascading effects on the composition and diversity of associated communities. Using a provenance trial, which excludes confounding environmental factors, the effects of tree phenotypic traits on the insect herbivore and microbial endophytic community were tested, in the first instance, using the Quercus study system. A leaf morphometric analysis allowed for accurate differentiation of the two native oak species, Quercus robur and Q. petraea. Interspecific variation in the composition of insect herbivore species and in the composition of bacterial and fungal endophyte species were recorded in the two oak species for the first time. The plant vigour hypothesis, which states that insect herbivores would preferentially feed on the most vigorous plant, was supported by the galling and mining insect feeding guilds in this study system but had varying effects on the endophytic species. Tree budburst phenology, another phenotypic trait, also had varying effects on the abundance of insects and endophytes. Quercus trees in the UK are expected to experience profound changes in climate. In an effort to maintain oak species, assisted migration schemes may be implemented, which involves the planting of seed stock from exotic provenances that match the predicted climate of the planting site in 50-100 years. This study considers the effect of this approach on the associated biodiversity. Insect and endophyte composition, richness and diversity were not strongly correlated with tree provenance, so it seems unlikely that climate matching strategies would strongly negatively impact these associated communities. As the UK climate warms, walnut trees (Juglans spp.) may become a more commercially viable source of hardwood timber. This study characterised the endophytic community of two introduced walnut trees in the UK: Juglans nigra and J. regia. A number of latent pathogenic fungi and bacteria were associated with asymptomatic tissues of both Quercus and Juglans, these species have the potential to cause disease if the tree is subjected to stress such as climate change and should therefore be monitored. Finally, the effect of a decline syndrome, Acute Oak Decline (AOD) which causes bleeding cankers among other symptoms on native oak species in the UK, on the endophytic community of oak was recorded. Bacterial endophyte communities did not differ between symptomatic and asymptomatic trees. However, differences in the fungal endophytic community associated with the inner bark of trees showing symptoms of AOD were significantly different from asymptomatic trees. This result suggests that (1) there could be a fungal component(s) to AOD that has not been reported or (2) asymptomatic trees harbour beneficial fungal endophytes that protect against AOD.