Invasive Lespedeza

Lespedeza cuneata is shrubby legume native to Asia, but it is considered to be a noxious, weedy invader of prairies and old field communities in North America, where it can displace native plants. L. cuneata has a high capacity for nitrogen fixation, and its litter has been show to have some allelopathic properties, so its arrival can affect the soil ecosystem and the plant and microbial communities in many ways. We are studying how L. cuneata affects the soil microbial communities of invaded sites, and we are also trying to understand how interactions with soil microorganisms can affect the establishment and population growth of L. cuneata.

Shrub Encroachment on Hill Prairies

Hill Prairies are unique ecosystems that occur along erodible, southwest-facing slopes along major river valleys in the midwestern U.S. They have a dryer, warmer microclimate than the surrounding bluffs, and this leads to the dominance of grassland vegetation over forest. They represent some of the last untouched prairie habitat in the state of Illinois. However, decades of fire suppression have lead to the slow loss of hill prairie habitat, as trees and shrubs from the surrounding forest encroach upon the open prairies. In the Yannarell lab, we are studying how the transition from prairie, to shrubland, to forest affects the soil microbial communities in these systems, and we are looking to see if microbial interactions are playing a role in this succession to forest. We are also investigating how soil microbial communities respond to conservation and restoration activities. In addition, because hill prairies are like “islands” of grassland habitat in a “sea” of forest, we are also interested in studying how the spatial configuration of these habitats influences microbial dispersal, species interactions, evolution, and extinction.

Invasive Shrubs

The forests of Illinois and much of the Eastern U.S. are facing invasions by a number of different shrubs, including bush honeysuckle (Lonicera mackii) and common buckthorn (Rhamnus cathartica). These shrubs can dramatically change the layer of plant litter that blankets the forest floor, which has many consequences for tree germination rates, forest floor food webs, and nutrient cycling. Many invasive shrubs have extended phonologies in comparison to native plants, meaning that they leaf out earlier in the spring and/or keep their green leaves later into the fall. This can extend the annual window over which the plants can interact with soil microbes. In addition, may invasive shrubs increase the rate of nutrient cycling in the forest soils, resulting in large ecosystem changes. In the Yannarell lab we are studying shrub invasions of forests to understand how microbes participate in these ecosystem changes. We are also trying to understand whether interactions with soil microbes can facilitate shrub invasion and whether we can use these interactions to help us manage shrub invasion.

Precision Zonal Management

Precision zonal management (PZM) is an attempt to encourage a broader set of ecosystem services from the soils of agricultural systems. While conventional agriculture has a tendency to treat a farm field as a single unit, there is a great deal of environmental and biological heterogeneity at many smaller scales. Precisions zonal management uses spatially confined tillage practices in attempt to create heterogeneity that can support different, and sometimes incompatible, processes in different side-by-side soil zones. We are looking at a type of PZM called “ridge-tillage,” where crops are planted on raised ridges above the surrounding soil; the pattern of ridges and furrow across the farm field establish the different zones. Ridges support the nutrient and water uptake by the crop, while furrows serve as sites for weed control, in-field composting and decomposition of plant residues, carbon accumulation, and soil building.

The PZM work in the Yannarell lab is part of a much larger research effort involving scientists from Minnesota, Michigan, Pennsylvania, New Hampshire, and Utah. The Yannarell lab is studying small-scale hetogeneity in microbial community composition in PZM systems, and we are also investigating how these systems affect microbial control of ecosystem function and they promote interactions between microbes, crop plants, and weeds.

Bat White Nose Syndrome

White nose syndrome (WNS) is a deadly disease affecting North American bat populations. The causative agent of the disease is a fungus known as Pseudogymnoascus destructans (formerly Geomyces destructans), which was first discovered in a cave in New York state in 2006. It has since been moving west, devastating bat populations along the way. The Yannarell lab is working with collaborators from the Prairie Research Institute, and our group discovered the first cases of P. destructans in Illinois caves in the winter of 2013. WNS is in its earliest stages in Illinois bat populations, so our research group is in the position to document the changes that happen to cave ecosystems when this fungus arrives. Because P. destructans is closely related to soil-dwelling fungi, it can persist in cave soils even after the local bat populations have been driven to extinction. In our work, we want to learn how P. destructans integrates itself into the normal microbial communities of cave soils, walls, and ceilings, as well as how the fungus affects the normal skin- and fur-associated microbial communities of infected bats. We hope that a better understanding of the ecology of this organism will teach us how we can prevent it from spreading to new caves and to effectively remove it from caves.

Microbial Communities and Weed Control

With growing interest in organic and low-input agriculture, and in the face of emerging herbicide resistance in a number of agricultural weeds, there is a need to look for alternative methods of weed control. The use of cover crops and green manures–where fresh cover crop residues are plowed directly into the soil prior to seeding of the cash crop–are methods that take advantage of naturally-occurring compounds present in cover crop litter as well as ecological principles like competition and plant-soil-microbe feedback. In the Yannarell lab, we are investigating the roles that soil microbial communities can play in weed control efforts. Soil microbes can degrade weed-suppressive compounds present in cover crop litter, making the soil a more hospitable place for germinating weeds and germinating cash crops. However, soil microbes can also be stimulated to attack germinating plants, making them potential natural agents of weed control. Learning more about the ecology of soil microbial communities will help us develop strategies to fine-tune these microbial functions, potentially allowing farmers to “turn-on” weed-suppressive microbes prior to crop planting, and then turn them back “off” to protect the health of the cash crop. In addition, we are studying whether the concept of plant-soil-microbe feedback can be used in combination with various cover crop rotations for the long-term development of weed-suppressive agricultural soils.

Invasive Stiltgrass

Japanese stiltgrass (Microstegium vimineum) is a shade-tolerant grass that can invade forests. It can completely dominate the herbaceous layer along the forest floor, choking out native plants and altering the properties of the plant litter that serves important ecological functions for many forest organisms. Japanese stiltgrass also changes the way nutrients are cycled in the soil, because it increases the rate of nitrification, which is the process by which ammonium is converted to nitrate. This is a microbial process, largely controlled by two major groups of soil microorganisms, known as the ammonia-oxidizing archaea and the ammonia-oxidizing bacteria. Right now, we do not know how Japanese stiltgrass interacts with these organisms to change the nitrification rate when it invades. The Yannarell lab is using the tools of molecular microbiology to study changes in the population sizes and community composition of these two groups of microbes, and we are also using special incubation assays to study the contribution of each one to the overall nitrification rate. We hope to uncover the mechanism by which Japanese stiltgrass changes the nitrogen cycle in order to better understand how to manage the ecosystem changes that are caused by this invader.

Plant Chemistry and Soil Microbial Communities

Plant chemistry can be a primary driver of microbial community composition and function, and it can be a primary controller of ecosystem function. In the Yannarell lab, we are particularly interested in understanding how “nitrogen-fixing” plants and allelopathic plants can affect microbial community structure and function. We are studying both legumes, which are plants that associate with nitrogen-fixing bacteria in the order Rhizobiales, and actinorhizal plants, which associate with nitrogen-fixing bacteria in the genus Frankia. Examples of the former are soybeans, lupines, lespedezas, and black locust; examples of the latter are alder and invasive autumn olive. We are studying how legumes and actinorhizal plants affect the processing of carbon and nitrogen in soil that is in contact with their roots and leaf litter, and we are particularly interested in understanding how these plants affect the processing of allelopathic compounds, which are plant-derrived compounds that have negative effects on other plants. We are investigating the interaction between these plants and soil microbial communities in a mixed planting of black walnut (allelopathic), black locust (legume), and autumn olive (actiorhizal). We are also studying a variety of ecosystems that are undergoing invasion by Lespedeza cuneata (a possibly allelopathic legume) and autumn olive.