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Research Projects: 
Plants, Soils, Plants and Invasion, Vegetation Monitoring

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.

Testing the effect of fire retardant (FR) and arbuscular mycorrhizal fungi (AMF) on slender wheatgrass and blanket flower in a greenhouse experiment.

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.

The orange color of fire retardant is visible using Google Earth.

Orange retardant is visible on rocks and logs as Abigail Marshal samples plants.

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).


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 Author

Ylva 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.