Year of Award
2025
Document Type
Dissertation
Degree Type
Doctor of Philosophy (PhD)
Degree Name
Systems Ecology
Department or School/College
Department of Ecosystem and Conservation Science
Committee Chair
Diana L. Six
Commitee Members
Ylva Lekberg, Richard Sniezko, Philip Ramsey, James Elser
Keywords
bark beetles, conifers, ectomycorrhiza, fungi, symbioses, terpenes
Abstract
Symbioses of fungi with trees and insects play outsized roles in forest ecosystems, influencing tree growth, defense, physiology, and nutrient cycling. While their functional contributions are widely recognized, they remain poorly understood. I integrate findings from three studies examining fungal interactions with conifers and with bark beetles to highlight their significance in tree resistance to disease, nutrient redistribution within the tree, and forest ecology.
First, I demonstrate that foliar fungal endophytes and ectomycorrhizal fungi, together and independently, can enhance resistance in Pinus monticola seedlings against Cronartium ribicola, the pathogen responsible for white pine blister rust. Symbiont inoculation induced host terpene defenses and reduced disease symptoms in seedlings, while promoting growth in pathogen-free conditions. These findings encourage the consideration of fungal interactions in tree breeding programs aimed at improving resistance to invasive pathogens. Second, I demonstrate that non-specific fungal symbionts of bark beetles can be beneficial to the insect host. Most research on bark beetle-fungal symbioses has focused on beetles that maintain highly specialized fungal partnerships. Instead, I investigated the red turpentine beetle (Dendroctonus valens) that associates with a dynamic consortium of fungi that shifts in time and space. Through a field study and stable isotope tracing, I documented how these fungal consortia enrich phloem—normally poor in nitrogen and phosphorus—through nutrient transfer from sapwood to phloem enhancing beetle nutrition and reshaping the broader fungal decomposer community, accelerating wood decay. Notably, my results show that even beetles in non-obligate fungal symbioses benefit from microbial-mediated nutrient provisioning and that consortium fungi are superior to non-consortium taxa in provisioning nutrients. The discovery that beetle-associated fungi alter decomposer communities and density loss underscores the broader ecological consequences of beetle-fungus symbioses, extending beyond beetle nutrition to forest carbon storage and nutrient cycling.
Finally, to better understand how fungal symbioses may change under a changing climate, I performed a meta-analysis of global conifer foliar endophyte biodiversity, and assessed the relative drivers, (i.e., host filtering, climatic filtering, and dispersal limitations) that determine global endophytic fungus distributions. These findings provide the first comprehensive assessment of conifer foliar endophyte diversity, emphasizing the interplay between host filtering and environmental factors.
Together, these studies highlight the diverse ecological roles of fungal symbionts, from enhancing tree defense and beetle nutrition to shaping microbial diversity and ecosystem processes in forests worldwide.
Recommended Citation
Bullington, Lorinda Sabin, "FUNGAL SYMBIONTS AS HIDDEN ARCHITECTS OF FOREST HEALTH: FROM TREE IMMUNITY TO BEETLE NUTRITION" (2025). Graduate Student Theses, Dissertations, & Professional Papers. 12486.
https://scholarworks.umt.edu/etd/12486
© Copyright 2025 Lorinda Sabin Bullington