Plants live in tight association with microbes, especially belowground where fungi and bacteria live on and inside the roots of plants. The relationship can be beneficial or harmful to the plant. Some microbes cause plant diseases by decomposing roots. Others trade nutrients with the roots in return for sugars produced aboveground by leaves.
We investigate two main aspects of the relationship between plants and microbes in the soil. First, as it pertains to weeds, we want to know if soil microbes can help or hinder plant invasions. Three highly invasive weeds of contrasting life history strategies; cheatgrass, knapweed and leafy spurge, co-occur with remnants of native plant vegetation. This creates a unique opportunity to observe, characterize, and manipulate interactions between plants and belowground microbial communities. We outline a number of short, intermediate and long-term research projects that will significantly enhance our knowledge regarding plant microbe interactions and soil processes, with the overall goal to better understand, predict and counteract plant invasions, and to restore and manage invaded ecosystems.
Second, we seek to understand how the relationship between plants and soil influences the function of ecosystem processes. Soil microbes are responsible for organic matter decomposition and nutrient cycling between the atmosphere and the land. On this project we collaborate with the Earth Microbiome Project (EMP). The goal is to map and understand the diversity of microorganisms in habitats around the world. We mapped microbial diversity and function across gradients of weed invasions.
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).
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.
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 have allowed her to explore the role of mycorrhiza, a root-fungus symbiosis, for geothermal plants in Yellowstone National Park and coastal grasslands in Denmark. Her research has been published in journals such as Ecology, Journal of Ecology and New Phytologist.
Ylva currently works at MPG Ranch as a soil ecologist. She explores the role of mycorrhiza in the success of exotic plants and examines the use of specific pathogens to combat invasions. In her spare time Ylva mountain-bikes, plays soccer, and maintains a large vegetable garden.