Date of Award

Spring 5-15-2022

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

Frank, Douglas A.

Second Advisor

Fridley, Jason D

Keywords

arbuscular mycorrhizal fungi, invasion ecology, mycorrhizas, plant ecology, root functional traits

Subject Categories

Biology | Ecology and Evolutionary Biology | Life Sciences

Abstract

Exotic species invasions present a global issue that is expected to worsen with the extreme conditions brought about by global climate change and anthropogenic disturbance. Invasive plant species in particular exhibit ecological, economic, and cultural effects on contemporary issues such as biodiversity, ecosystem processes and global food security. Understanding the factors governing both the invasion process and the species that become invasive are important tools for lessening the impacts of plant invasion, as well as preventing future invasions. This dissertation focuses on belowground aspects of these invasive species, including linking arbuscular mycorrhizal fungi (AMF) to invader growth responses, investigating the relationships between AMF community composition and their plant hosts, and understanding the syndromes of fine root functional traits that form based on plant invasive status and AMF colonization. Using softwood cuttings of phylogenetically paired native and invasive shrubs from a common garden, plants were grown under high and low nutrient conditions, as well as with or without live soil inoculum containing AMF propagules. I used biomass data to assess if natives or invaders had different mycorrhizal growth responses, and if previously field-collected leaf traits correlated with growth and resource-use strategies. Invasive shrubs grew faster regardless of AMF status, but native shrubs exhibited greater mycorrhizal growth response. More resource-acquisitive species also showed greater mycorrhizal growth responses under low nutrient conditions. However, the effects of AMF colonization on plant growth responses did not account for variation due to AMF species identity. Consequently, in a follow-up study I sequenced AMF communities with the Illumina MiSeq platform. By providing plants with a single inoculum source, I was able to determine if unique AMF communities formed in association with plant host nativity, phylogeny and nutrient availability. AMF communities were largely unaffected by nutrients and plant nativity, but plant phylogeny had a small but significant effect on AMF composition. In order to more fully understand the mechanisms behind AMF-mediated growth responses in invaders I used measurements of eight fine root functional traits to determine the interactions between nativity, phylogeny and mycorrhizal inoculation. Phylogeny explained most of the variation in root traits, and a PCA revealed distinct nested patterns of nativity and AMF inoculation. Traits were organized into a framework with one axis defined by morphological and architectural traits and a second axis consisting of root resource traits. Overall, my results support that invasive plants interact with a largely similar AMF community as native plants, but that resulting growth and allocation from the interactions differ. These differences include invaders' lower mycorrhizal growth responses, shorter first order roots and greater root branching. Nativity effects are also complicated by plant host phylogeny, with some native-invasive contrasts developing only in certain plant families. Together, these experiments incorporate the interrelated aspects of root functional traits, AMF communities and plant phylogeny to better understand the belowground ecology of exotic plant invasion.

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Open Access

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