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For a non-scientist’s description of the Evans Lab’s research, see Communication
Our research can be divided into three broad themes:
Our research can be divided into three broad themes:
1. Microbial decomposition and water dynamics
Aerial view of fog coming in from the coast into the sand dunes of the central Namib Desert, Namibia, Southern Africa.
Drylands cover 41% of global land area (Reynolds et al. 2007) and play a central role in the global carbon cycle (Lal et al. 2004, Scurlock and Hall 1998). However, ecosystem models can be poor predictors of decomposition in these areas, suggesting our understanding of dryland decomposition is incomplete. Microbes could play an important role in this regard if they have unique physiologies that tolerate drought, but indirect effects of drought (e.g. change in plant community composition), make it difficult to isolate this effect (Evans et al. 2013, Ecosystems). We are examining interactions between microbial communities, UV photodegradation, dew- and humidity-induced decomposition, and rainfall pulses to better understand dryland decomposition. A focal site for this work is the Namib Desert, Namibia, where we work in collaboration with Kathy and Peter Jacobson, Mary Seely, and Roland Vogt (see Jacobson et al. 2015). Robert Logan (Evans Lab graduate student) is also examining UV photodegradation and other aspects of this extreme ecosystem for his dissertation. This work is currently funded by National Geographic, Grinnell College, and MSU African Studies Program.
Research related to this theme is also ongoing at KBS LTER and GLBRC, where the climate is expected to become more extreme, leading to longer dry periods. Previous work has shown that microbial life history strategies shift in response to this stress (Evans et al. 2014, Ecol Lett), and that microbial community composition alters the nature of the CO2 pulse that is induced after rewetting (Evans et al. 2015, SBB). We are interested in the implications of the prediction of more drying-rewetting cycles in Michigan, which is likely to alter microbial diversity, greenhouse gas flux, and crop yields. To examine microbial responses to drying-rewetting, we have developed assays to quantify microbial desiccation tolerance, and metabolomics proxies for drought tolerance strategies.
Research related to this theme is also ongoing at KBS LTER and GLBRC, where the climate is expected to become more extreme, leading to longer dry periods. Previous work has shown that microbial life history strategies shift in response to this stress (Evans et al. 2014, Ecol Lett), and that microbial community composition alters the nature of the CO2 pulse that is induced after rewetting (Evans et al. 2015, SBB). We are interested in the implications of the prediction of more drying-rewetting cycles in Michigan, which is likely to alter microbial diversity, greenhouse gas flux, and crop yields. To examine microbial responses to drying-rewetting, we have developed assays to quantify microbial desiccation tolerance, and metabolomics proxies for drought tolerance strategies.
Aerial photo of part of Kellogg Biological Station. Gull Lake lies in the background, and experimental agricultural plots in the foreground - a great place to address both basic and applied research questions
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Methods highlight: Coupling isolates and whole-community 'omics: We employ both culturing and metagenomics techniques, and find the combination of the two effective for probing hypotheses and relationships between physiology, diversity, and function. We have currently developed a high throughput assay for assessing single-isolate desiccation tolerance and population dynamics under drying-rewetting, providing information on physiological strategies for tolerating moisture fluctuation that we can then link to metagenomic or metabolomics data in the whole-community.
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2. The role of microbial dispersal in community and evolutionary processes
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pMicrobes disperse long distances and in great abundances in precipitation, air, and through hosts. Recently, as Baas-Becking’s hypothesis that ‘everything is everywhere and the environment selects’ is challenged by empirical observations, dispersal has received greater recognition as a process shaping microbial community composition. However, the specifics are still unclear. How much does dispersal matter, compared to other things like species filtering? What determines how invadable a community is? How do different aspects of dispersal like rate and colonizer taxonomy and traits affect extant communities?
We recently addressed how dispersal interacts with selection to alter stochasticity in microbial community composition (see Evans et al. 2016, ISMEJ). In the Evans lab, we are now exploring dispersal and colonization in microbial communities in two ways. First, we are characterizing the composition of dispersing communities in air, rain, and fog in two systems, and quantifying the effect of this ‘input’ on soil (or litter) community dynamics and function. Second, graduate student Heather Kittredge (in collaboration with lab manager Kevin Dougherty) is asking how colonizing microorganisms, and specifically their genetic material, move through extant communities through replication and horizontal gene transfer. |
 Fungi (puff ball) releasing spores that are dispersed by wind
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Methods highlight: individual-based models. We have used models to study both microbial assembly and microbial linkages to ecosystem function. The movie to the left shows a simulation of microbial cells on a soil micro-grid (1 square milimeter!). Different colors represent different microbial functional groups (e.g. cheaters). Individuals compete and are filtered on the grid over time. We used this model to study the role of microbial physiology - and community composition - in drying-rewetting pulses (Evans et al. 2015) with Tina Kaiser at the International Institute of Applied Systems Analysis.
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3. The rhizosphere microbiome and soil nitrogen availability in degraded lands
Major objectives of DOE-funded MMPRNT project. In the root zone, microbial dynamics interact with plant root exudation to influence N availability for bioenergy crops.
Nitrogen (N) is the most limiting nutrient to plants on earth. Maintenance of crop yields in most areas rely on chemical fertilizer, which is costly and can be harmful to the environment and human health. Free-living N fixers in soil can provide a biologically-based source of nitrogen to crops. This source of N may be especially important for crop growth in degraded lands, or marginal lands, that exhibit low productivity. In this DOE-funded project in collaboration with Lisa Tiemann, Maren Friesen, and Jim Cole (all MSU), we are examining how the rhizosphere microbiome contributes to the productivity of perennial grasses that can be used for cellulosic bioenergy production. Plants such as switchgrass could stimulate beneficial N-fixing organisms by secreting exudates from their roots, but may have less incentive to do this when fertilized, decreasing the N-fixing capacity of the soil. We are examining plant and microbial traits associated with nitrogen cycling in the Marginal Land Experiment of the Great Lakes Bioenergy Research Center (GLBRC), at Michigan State University and University of Wisconsin.
We call this project "MMPRNT", Microbially Mediated Perennial Rhizosphere Nitrogen Transformations. In the Evans Lab, Will West (root exudate-microbe interactions) and Tayler Chicoine (effect of plant genotype on microbial communities) are both working on this project, but there are many other participants as well. See the MMPRNT website, designed by our excellent project manager Steve Gougherty, for more information.
Funding: DE-FOA-0001207.
See press on this grant in MSU Today
See pictures from the field on our Field Pictures page.
We call this project "MMPRNT", Microbially Mediated Perennial Rhizosphere Nitrogen Transformations. In the Evans Lab, Will West (root exudate-microbe interactions) and Tayler Chicoine (effect of plant genotype on microbial communities) are both working on this project, but there are many other participants as well. See the MMPRNT website, designed by our excellent project manager Steve Gougherty, for more information.
Funding: DE-FOA-0001207.
See press on this grant in MSU Today
See pictures from the field on our Field Pictures page.
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Methods highlight: stable isotopes. An exciting aspect of this project is the use of isotopes to study plant-microbe interactions. We are developing a pulse-chase method using 13CO2 labeling to quantify rates of root exudation in switchgrass, and also using stable isotope probing (SIP) to characterize which microbes use which C and N compounds.
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Other projects and collaborations:
- Does microbial community diversity display land-use legacies? In collaboration with Nash Turley, Lars Brudvig (Plant Biology, MSU), and Will West, we are examining microbial community composition in abandoned agricultural sites at the Savannah River Site in South Carolina
- How does the guppy gut microbiome interact with its rapid evolution in Trinidadian streams? In collaboration with Sarah Fitzpatrick (IBIO, MSU), we are examining how host-associated microbes are dually influenced by the genetics and traits of their host and environmental factors, which may influence evolution.
- Do aridland grass endophytes get first dibs as decomposers? This project examines fungal endophyte ecology and taxonomy in Stipagrostis sabulicola grass in the Namib Desert. It is currently led by Kathy Jacobson (Grinnell College) and Anthony Wenndt (now at Cornell University).
Catching guppies in streams in Trinidad to study how gut microbiomes change as fish evolve.
References Cited
- Reynolds, J. F., Smith, D. M. S., Lambin, E. F., et al. 2007 Global desertification: building a science for dryland development. Science 316, 847–51.
- Lal, R. 2004 Carbon sequestration in dryland ecosystems. Environ. Manage. 33, 528–544.
- Scurlock, J. M. O. & Hall, D. O. 1998 The global carbon sink: a grassland perspective. Glob. Chang. Biol. 4, 229–233.
- Whitford, W., Meentemeyer, V., Seastedt, et al. 1981 Exceptions to the AET model: deserts and clear-cut forest. Ecology 62, 275–277.
- Jacobson, K., van Diepeningen, A., Evans, et al. 2015 Non-rainfall moisture activates fungal decomposition of surface litter in the Namib Sand Sea. PLoS One 10, e0126977.
