Native and exotic plant root traits and arbuscular mycorrhizal fungal community composition and function.

Abstract

The goal of my thesis was to study the link between plant root traits and arbuscular mycorrhizal fungal traits, and how the arbuscular mycorrhizal fungal communities of native and exotic plants differ.

I began my research by characterizing the arbuscular mycorrhizal fungal community of a wide range of native and exotic plant species ranging in root diameters (Chapter 2). I found that plant root diameter had a strong influence on the composition of arbuscular mycorrhizal fungal communities. Coarse-rooted plants associated with a lower diversity of arbuscular mycorrhizal fungi compared to fine-rooted plants, suggesting the presence of host-partner specificity. Arbuscular mycorrhizal fungal communities were also different between native and exotic plants, with exotic plants associating disproportionately more with the most dominant fungal families in my study.

Knowing that fungal communities were influenced by root diameter, I then undertook a greenhouse experiment (Chapter 3). In this experiment I inoculated a range of host plants with live root fragments of the 30 species from Chapter 2 in a multi-compartment pot to quantify the functional traits of the respective arbuscular mycorrhizal fungal communities. I found that arbuscular mycorrhizal fungal communities associated with coarse-rooted plants produced more hyphal biomass and explored soil further away from the roots of host plants compared to fungal communities from fine-rooted plants. Sequencing the arbuscular mycorrhizal fungal community near and far away from the roots also allowed me to identify which fungal taxa could be responsible for the increase or lack of hyphal abundance further from the roots.

Lastly, I characterized the arbuscular mycorrhizal fungal communities in constructed plant communities (Chapter 4) ranging in exotic dominance (0% - 100%) allowing me to scale up my finding from individual species to plant communities. I found that increasing exotic dominance decreased arbuscular mycorrhizal fungal diversity. However, plant communities with more coarse-rooted plants maintained the same arbuscular mycorrhizal fungal diversity even when exotic dominance increased. Exotic dominance also led to an increase of associations with generalist fungal partners.

The overall results of this thesis showed complementarity between plant root traits and arbuscular mycorrhizal fungal traits. This is vital understanding for restoration planting, showing the importance of matching plants with mycorrhizal partners able to complement root traits. The role of plant community structure is also vitally important in preserving below ground diversity during plant invasion. My work highlighted the value of moving past a ‘one fungus – one plant’ framework to understand mycorrhizal function and to examine how arbuscular mycorrhizal fungal communities respond to plants more holistically.