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.
Fungal endophytes are microorganisms that live inside plant tissues without causing apparent disease. They often compete with other microorganisms by producing toxic defensive compounds. Western white pines may increase their defenses against forest pathogens, like Cronartium ribicola, the causal agent of white pine blister rust, by hosting diverse fungal endophyte communities. If fungal endophytes produce compounds that can inhibit the growth of C. ribicola, they may also have potential to decrease damage from white pine blister rust disease in infected trees.
To test for inhibition of C. ribicola from fungal endophyte compounds, we used a cell viability indicator dye, resazurin. This highly sensitive method can detect cell viability in as few as 40 living pathogen cells.
Resazurin is used often in medical and agricultural research but is relatively new to the field of ecology. The dye enters living cells and changes from weakly-fluorescent blue to highly-fluorescent pink with active metabolism (Figure 1). Dead cells have no active metabolism and don’t change the dye.
We can use resazurin to compare and quantify fluorescence or cell viability between pathogens grown with and without endophytic defensive compounds. So far, we have screened over 70 endophytes for antimicrobial compounds that inhibit C. ribicola metabolism in vitro. The most inhibitory compounds reduced C. ribicola metabolism by >30% after just a few days of exposure (Figure 3).
We selected the endophytes with compounds most inhibitory to C. ribicola and sprayed them onto hundreds of western white pine seedlings in a full factorial greenhouse experiment. We will expose these seedlings to the pathogen in September to determine if endophytes can indeed decrease damage in infected trees.
Emily graduated from Montana State University in 2016, earning a B.S. in Biological Sciences with a concentration in Conservation Ecology & Biology and minor in Statistics. While in school, she spent time at MPG Ranch capturing and monitoring painted turtles.
After finishing her degree, Emily worked as a microbiology intern at MPG where she prepared samples for DNA sequencing and cultured fungi from plant tissue. Upon completing her internship, Emily transitioned into her current role as a laboratory technician where she assists with projects relating to plant-fungal interactions, natural history, and light microscopy.
Outside of work, Emily enjoys reading, fishing, and riding her horses across Montana’s beautiful landscape.