
How Does Fire Retardant Influence Arbuscular Mycorrhizal Fungi?
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Soils Plants and Invasion
Plants live in tight associations with microbes who colonize their roots and leaves and surrounding soil. Some microbes are harmful and cause disease while others are beneficial and aid in plant nutrient uptake, decomposition of organic materials, protection against pathogens, tolerance against drought and other stressors. Plants can influence microbial communities and vice versa with consequences for the growth of individual plants, the composition of plant communities, and entire ecosystems. In our work, we focus on three main aspects of plant-microbe interactions; 1) how they may aid or hinder plant invasions, 2) how their function changes across environmental gradients, and 3) how they may both cause and prevent disease in plants.On MPG Ranch, three highly invasive weeds of contrasting lie history strategies (cheatgrass, knapweed and leafy spurge) co-occur with remnants of native plant vegetation. Using both observational and experimental approaches, we seek to understand how these weeds alter microbial communities and how this influence invasive success, ecosystem properties and restoration. We also collaborate with researchers from across the world to learn if plant-microbe interactions differ between native and invasive ranges and how this correlates with evolutionary shifts in plant genomes and biogeographical distribution of plant associated microbes.
Outcomes of plant-soil microbe interactions depend on the particular plant and fungal species and surrounding environmental conditions. To explore this context-dependency, we use high-throughput sequencing and stable and radioactive isotopes in surveys and experiments to determine if the proportion of fungal guilds (mutualistic mycorrhizal fungi and potential pathogens) change with water and nutrient availability and how these changes relate to plant growth. Because most research occurs in single locations, the generality of findings across locations that differ in environmental conditions is often unknown. To address this, MPG Ranch is part of two global research collaborations, Nutrient Network (https://nutnet.org) and DroughtNet (www.drought-net.org). In these experiments, all researchers apply nutrients, remove herbivores, expose plants to drought, and record responses in both plant and microbial communities using the same protocols, which allow for direct comparisons across sites.
The invasive fungal pathogen, Cronartium ribicola, causes the disease commonly known as blister rust in all nine white pine species native to the United States. As one of the only labs in the world to grow C. ribicola in culture, we perform tests of pathogen metabolism when exposed to compounds produced by other fungi found in white pine needles. Greenhouse experiments inoculating trees with these fungi, as well as beneficial ectomycorrhizal fungi, explore how we can improve tree growth and disease resistance. We also use isotopes and controlled field experiments to determine how blue-stain fungi carried by bark beetles can influence wood decomposition in forest ecosystems. As warming climates increase the frequency of bark beetle outbreaks worldwide, this research will help to better estimate future forest carbon storage and release.
Vegetation Monitoring
Plants constitute the essential core of the ecosystem. Without plants, habitat exists only as an inhospitable void. Knowing that vegetation plays such an integral part in ecosystem function, we keep a close eye on the current state and subsequent changes in vegetation. One facet of vegetation research is vegetation data collection across MPG.
A grid of 560 sampling points covers MPG, with each point separated by about 200 yards. We visit each point to gather data on plant communities. At each point we set up 4 transects, each 50 feet long. Botanists record the plant species encountered at each foot. The reports in this section discuss how we categorize plant communities and the relationships between plant communities and other kinds of organisms.
As we continue to layer data onto this sampling grid we will post new discussions of interactions between plant communities and new groups of organisms. Rebecca Durham, one of the botanists that conducted the original survey, is revisiting many of the points to document lichen and moss community composition.
Smoke from forest fires in Idaho has covered the ranch for the past month and made fieldwork difficult. Aerial firefighters drop retardants that contain high levels of nitrogen (N) and phosphorus (P). Both N and P are plant nutrients that can promote growth, but high concentrations can kill plants and cause eutrophication of waterways. Previous research has shown that invasive cheatgrass (Bromus tectorum) increases in abundance and outcompetes native plants in the presence of fire retardant (Besaw et al. 2011). However, the effects of fire retardant on soil microbes are virtually unknown.
MPG Ranch worked with UM undergraduate Abigail Marshall to assess how fire retardants impact arbuscular mycorrhizal fungi (AMF). AMF are soil-dwelling mutualists that colonize plant roots and provide pathogen protection and nutrients in exchange for plant carbon. The high P levels in fire retardants can reduce AMF abundance and the services they provide. Abigail grew slender wheatgrass (Elymus trachycaulus) and blanket flower (Gaillardia aristata) with and without AMF and fire retardant in the greenhouse (Picture 1). Fire retardant increased growth in all plants, but the high concentration caused some burned tips. Preliminary data indicate reduced AMF colonization with retardant, especially in slender wheatgrass.
Picture 1. We tested the effect of fire retardant (FR) and arbuscular mycorrhizal fungi (AMF) on slender wheatgrass and blanket flower in a greenhouse experiment.
To relate greenhouse results to field conditions, Abigail and I chose an area that burned last year. We located sites with and without the orange retardant using Google Earth (Picture 2). Logs and rocks remained orange even one year after aerial drops (Picture 3). We sampled several native and exotic plants and will estimate mycorrhizal colonization of roots and measure soil nitrogen and phosphorus concentrations. This will tell us about long-term influences of fire retardants on plants and their associated soil microbes.
Picture 3. The orange fire retardant was still visible on rocks and logs, which made it easy to locate last year’s application areas (a). Abigail Marshall samples plants (b).
References
Besaw LM et al. 2011. Disturbance, resource pulses and invasion: short-term shifts in competitive effects, not growth responses, favor exotic annuals. Journal of Applied Ecology 48, 998-1006.
Smith, S.E. & Read, D.J. (2008). Mycorrhizal Symbiosis. Academic Press, Cambridge.

About the AuthorYlva Lekberg
Ylva graduated from the Swedish University of Agricultural Sciences with a M.Sc. in Biology and Horticulture in 1996 and a Ph.D. in Ecology from Penn State University in 2004. She received the Alumni Association Dissertation Award for her work in agroecology and subsistence farming in Sub-Saharan Africa. Post-doctoral positions at Montana State University and later at Copenhagen University as a Marie Curie Fellow allowed her to explore the role of arbuscular mycorrhiza, a root-fungus symbiosis, for geothermal plants in Yellowstone National Park and coastal grasslands in Denmark. Her research has been published in international journals such as Nature Communications, Ecology Letters, and New Phytologist.
Ylva joined MPG Ranch in 2010. Since then, she has explored how invasive plants common to western Montana, including spotted knapweed (Centaurea stoebe), leafy spurge (Euphorbia esula) and cheatgrass (Bromus tectorum), influence soil microbial community composition and function, and how this in turn may affect invasive success. A lot of her research also focuses on the AM symbiosis in terms of community ecology and physiology. A current project addresses how exchange ratios in this symbiosis may differ among co-occurring plants and depend on soil nutrient availabilities. She uses surveys, field and greenhouse experiments, and literature approaches such as meta-analyses to address questions. To learn more about research and publications from Ylva and her group, see CV below and the Soils, Plants and Invasion section.
In addition to her work at MPG Ranch, Ylva is an adjunct professor at University of Montana at the Department of Ecosystem and Conservation Sciences.
Ylva joined MPG Ranch in 2010. Since then, she has explored how invasive plants common to western Montana, including spotted knapweed (Centaurea stoebe), leafy spurge (Euphorbia esula) and cheatgrass (Bromus tectorum), influence soil microbial community composition and function, and how this in turn may affect invasive success. A lot of her research also focuses on the AM symbiosis in terms of community ecology and physiology. A current project addresses how exchange ratios in this symbiosis may differ among co-occurring plants and depend on soil nutrient availabilities. She uses surveys, field and greenhouse experiments, and literature approaches such as meta-analyses to address questions. To learn more about research and publications from Ylva and her group, see CV below and the Soils, Plants and Invasion section.
In addition to her work at MPG Ranch, Ylva is an adjunct professor at University of Montana at the Department of Ecosystem and Conservation Sciences.