McCarroll, Callah2026-05-122026-05-122026https://hdl.handle.net/1828/23883Plants host a diverse array of micro-organisms referred to as endophytes, which reside primarily in the interstitial spaces between plant cells. Endophytes often exist in complex communities composed of multiple species from multiple kingdoms, although fungi are the most common colonizers of plant tissues. These micro-organisms interact with each other and with the host, sometimes resulting in altered phenotypes for the host plant which can be beneficial or detrimental. Determining what drives the structure of these community assemblages is a key prerequisite for understanding the overall nature of microbial ecology. Douglas-fir trees (Pseudotsuga menziesii) are a keystone species threatened by disease, climate change, and human development, and like all plants, they harbour a diverse suite of fungal endophytes. In this research, the temporal dynamics of Douglas-fir foliar fungal endophyte communities was systematically characterized over an entire growing season. This was done by collecting Douglas-fir needles from 16 trees in a single location six different times over a calendar year. High-throughput sequencing-based metabarcoding was employed to amplify fungal ITS1 sequences for identification of fungal endophyte community members within Douglas-fir leaf tissue at different times of the year. Using both Alpha and Beta diversity measures, this research was able to show significant community dissimilarity between sampling months. This research also described a dominant unknown endophyte within the order of Mycosphaerellales appearing to have a negative relationship with Nothophaeocryptopus gaeumannii, a well studied Douglas-fir endophyte and causal agent of Swiss needle cast disease. This is the first seasonal description of fungal endophytes within Douglas-fir needles using meta-barcoding analyses. Supervisor: Dr. Jürgen EhltingenHonours thesisDepartment of Biology