Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Way, Danielle A

Affiliation

Australian National University, Canberra, Australia

2nd Supervisor

Thorn, Greg

Joint Supervisor

3rd Supervisor

Ramsfield, Tod

Affiliation

Northern Forestry Centre, Edmonton, Alberta, Canada

Co-Supervisor

Abstract

Climate change poses significant challenges to forests worldwide, particularly the Canadian boreal forest. Populus spp. are ecologically and economically important tree species that have had declining growth and survival due to elevated temperatures and droughts associated with climate change. Symbiotic microbes, such as mycorrhizal fungi, may increase plant growth under climate change conditions by altering tree metabolic profiles and increasing tree access to water and nutrients. My thesis explores the relationship between mycorrhizal fungi and a Populus hybrid (Populus x canadensis) grown under a range of future climate scenarios: ambient CO2 (400 ppm) or elevated CO2 (750 ppm) with either ambient temperatures or a +4 ˚C or +8˚C warming treatment. My primary objective is to assess how mycorrhizae influence growth, stress phytohormone concentrations, and stress tolerance of hybrid poplar under predicted future climatic scenarios. Additionally, I identify compounds exuded by mycorrhizal fungi and evaluate their potential to enhance plant growth. My findings reveal that different boreal mycorrhizal fungi produce similar profiles of phytohormones, amino acids, and organic acids in their exudates. The exudates of some mycorrhizal fungi enhanced plant growth, while others caused mortality. In my hybrid poplar growth study, the colonization of poplar roots by mycorrhizal fungi increased with elevated temperature and CO2. Inoculation with mycorrhizal fungi did not increase tree height or mass, with the exception of trees grown under +4 ˚C warming, where total biomass increased by ~15% compared to control trees. Unexpectedly, inoculation with mycorrhizal fungi almost always increased hybrid poplar mortality. To understand why mycorrhizal inoculation increased mortality but improved the growth of surviving hybrid poplars, I investigated the impacts of climate change and mycorrhizal inoculation on plant stress hormone concentrations. Mycorrhizal inoculation generally increased leaf concentrations of the stress hormone jasmonic acid, while the stress hormones salicylic acid and abscisic acid had reduced leaf concentrations across elevated temperature and CO2 treatments. Overall, my research contributes valuable insights into the intricate connections between mycorrhizal fungi, trees and climate change, offering a better understanding of forest ecosystem resilience in the face of environmental challenges.

Summary for Lay Audience

In our changing world, the health of forests is at risk due to climate change, especially in the Canadian boreal forest. One important group of trees, Populus (poplars), is crucial for understanding how these changes affect trees. Almost all plants, including poplars, form partnerships with soil fungi called mycorrhizal fungi, and to date, little research has been done on how climate change could impact this relationship. These fungi establish a mutually helpful relationship with tree roots, giving them water and nutrients in exchange for sugars from the trees. This relationship is thought to increase resilience to environmental stresses, such as elevated temperatures that accompany climate change. My research focused on exploring this association between mycorrhizae and a poplar hybrid in the face of climate change. I studied how associating with these fungi would affect tree growth and stress tolerance to high CO2 and temperatures. I also looked into the substances released by these fungi, checking if they could help plants grow. I found that the fungi release certain substances that, when applied to plants, can either improve growth or harm them. Even though warming alone didn't affect tree growth much, 4 °C warming combined with high CO2 made the trees without fungi larger, but increased tree death rates. I also discovered that fungi increased their association with tree roots in warmer conditions but at the cost of higher tree mortality. In summary, my research helps us understand the association between mycorrhizal fungi and trees under climate change. By figuring out how these organisms work together, we can learn how to better protect our forests in a warming world.

Download

Share

COinS