Advisor(s): Rhae Drijber, Josh Herr
Ashley received her Bachelor of Science degree in Biology from the University of Utah, graduating with an Undergraduate Research Scholar Designation for her work with Dr. Denise Dearing and Dr. Kevin Kohl (paper). Ashley entered the Complex Biosystems Program at UNL in Fall 2015 as part of the first cohort. She is pursuing a PhD with a specialization in microbial interactions under the mentorship of Drs. Rhae Drijber (Department Agronomy and Horticulture) and Joshua Herr (Department Plant Pathology).
Ashley's current research applies bioinformatics tools to investigate the ecology of soil microbes in maize agroecosystems. Considering both temporal and spatial dynamics at a long-term field site in Nebraska, Ashley is working to identify drivers of nutrient cycling and characterize the functional significance of microbe-microbe, microbe-environment, and microbe-host interactions. You can hear more about Ashley's work by listening to the Streaming Science podcast "Think Like a Microbe"
In addition to these research activities, Ashley has been able to explore her passion for teaching through designing, implementing, and teaching a professional development course for graduate students. In collaboration with Dr. Sydney Brown (Director, Center for Transformative Teaching) and Dr. Sydney Everhart (Department Plant Pathology) the "Success in the Sciences" course has been offered at UNL for two consecutive years.
Updates & Activities
2019 Tri-Society Meeting
This week the Drijber lab group is excited to be attending the 2019 ASA-CSSA-SSSA International Annual Meeting in San Antonio. Ashley is participating in the Soil Biology & Biochemistry Division Poster & 5 minute Rapid talk. Her presentation is titled "Crop Rotation History Shapes Soil Recruitment Pools of Maize Under Nitrogen Limitation" and her poster (# 1249) will be up for viewing on Monday, November 11. Graduate students Salvador Ramirez and Morgan McPherson will also be presenting their work at the conference on tuesday, November 12. Information on Salvador's talk can be found here and Morgan's two posters can be found here and here.
Crop Rotation Study (CRS) Field Site
In collaboration with the USDA, the Drijber lab group is studying the role of crop rotation and nitrogen fertilization on maize production and agroecosystem sustainability. Established in 1972, this rain-fed, no-till, long-term field site in Eastern Nebraska provides the platform for work evaluating the effects of management practices on soil habitat, maize yield, and microbial community structure and potential function. Ashley's work at this field site has focused on 4 different crop rotation histories: continuous corn (CCCC), corn-soybean (CSCS), corn-soybean-sorghum-oat/clover (CSGO), and corn-oat/clover-sorghum-soybean (COGS). Specifically, Ashley is interested in the role of crop diversification (CCCC & CSCS vs. CSGO & COGS) and crop sequence (CSGO vs. COGS) on maize-associated microbial communities under different nitrogen histories (high, low, zero). Combining discovery-driven exploration of microbial community patterns with hypothesis-testing to elucidate key microbe-host and microbe-environment interactions, Ashley has used findings from the CRS field site to inform greenhouse experiments to characterize the role of management history on rhizosphere assembly in early-stage (V1-3) maize seedlings.
Greenhouse Study Highlights
Initial results from a greenhouse study suggest that management history may drive differences in rhizosphere assembly on the same plant host species. Fatty Acid (FAME) profiling reveals that microbial community structure differs by crop and nitrogen management history, contributing to different microbial pools that may eventually colonize maize roots. Most importantly, analysis of these community profiles shows that under historically nitrogen-limited conditions microbial communities are more strongly shaped by crop rotation history.
Preliminary data on soil habitat suggests that crop diversification and nitrogen fertilization may be shaping communities through changes in organic matter, soil pH, and potentially available pools of carbon and nitrogen (water extractable C and N from Haney Tests). Analysis of the field soil used as source soil in the greenhouse experiment shows that crop diversification (more diverse in the CSGO and COGS rotations, and less diverse in the CCCC and CSCS rotations) is driving differences in soil organic matter content that may translate to differences in the microbial biomass supported under these different crop histories. Additionally, nitrogen fertilization histories has a strong effect on soil pH, whereby a history of high N-inputs acidifies the soil compared to low and zero N-inputs. Soil pH is known to be a major factor influencing microbial community structure and could be driving differences in microhabitats that overwhelm the role of crop diversification. Ashley is in the processes of analyzing soils from the greenhouse experiment to evaluate how carbon and nitrogen pools may shape microbial community structure.
The overarching goal of this project is to ascertain the influence of management history on assembly of the maize rhizosphere. To this end, Ashley is also investigating the rhizosphere and root compartments from this greenhouse study. She hypothesizes that the community composition of the source soil - shaped by management history - will be a larger driving factor in rhizosphere community structure than plant host identity. As such, she expects to see different rhizosphere communities across crop and nitrogen treatment groups. Given the selectivity inherent in root colonization (e.g. microbes have to be able to persist in the root environment and form associations with the host plant), Ashley expects to see more convergence in community structure across management histories, which may yield insight into a "core" maize root microbiome. In addition to community profiling and soil habitat characterization, the next step of this project will explore taxonomic diversity through amplicon sequencing and the functional potential of communities through enzyme assays and metagenomics.