Microbial community dynamics in tallgrass prairie soil affected by native grazer feces (Bison bison)

Advisors: Wesley D. Swingley.Committee members: Nicholas Barber; Holly Jones.Includes bibliographical references.Includes illustrations.Tallgrass prairies have been reduced in area by over 90% and are therefore one of the most threatened ecosystems in the world. Efforts to restore these native lands from agriculture are ongoing throughout the North American Midwest. Changes in the microbial community and ecosystem properties that follow conversion of agriculture to restored tallgrass prairies are poorly understood. In this work we sought to characterize how nutrient influx and microbial communities from reintroduced native grazer feces affected the microbial community of prairie soil during restoration. Nachusa Grasslands, located in Franklin Grove, IL, USA, is a successful long-term effort of restoring agricultural land to a mosaic of tallgrass prairies. More than 30 bison (species Bison bison) were reintroduced into 500 acres of enclosed prairie in November 2014 to reinstate integral grazing regimes to the landscape. Newly-reintroduced bison had access to restored prairies that were re-planted at nine different time-points over the previous 16 years, as well as remnant prairies that were never used for agriculture. Manipulative field experiments were used to explore the direct interactions between bison dung and prairie soil that differed in restoration age, with bulk soil from both bison-exposed and bison-free treatments sampled biweekly from spring to fall 2015. In addition, we sampled soil below and along a transect away from transplanted fecal patties during a three-week period to examine the direct impact of dung on soil geochemistry and microbial diversity. The mass quantification carbon and nitrogen and 16S rDNA amplicon sequencing were used to quantify nutrient influx and changes in microbial communities upon fecal introduction. Initial community analyses in 2015 suggested that feces inputs drove an increase in easily cultivable, acidophilic Acidobacteria Groups 1 and 3 in old and remnant prairies, but decreased these groups in a newly-planted prairie. Conversely, primarily uncultured, neutrophilic Acidobacteria Groups 6 and 16 show the opposite trend, suggesting that pH and nutrient concentration may have drastically different effects on different-aged prairies. Surprisingly, repeated experiments in 2016 found soils that appeared to have converged on a seemingly novel, homogenized microbial community structure. Further analyses of soil geochemistry and the reconstruction of microbial metabolism will determine if bison-mediated increases in nitrogen and carbon are directly responsible for these community shifts or whether bison transport, either through feces or physical disruption, is seeding a new prairie microbiota. Continuing studies at Nachusa Grasslands will establish whether changes in geological, ecological and microbial structure due to fecal deposits are temporary or have long-term impacts on both the prairie soil and higher trophic levels. Ecosystem restoration is a critical component of managing sustainable biogeochemical cycles in the Anthropocene, and characterizing the microbial contributions, in concert with plants, animals, insects, and fungi, will be critical to improving success rates for future restoration efforts.M.S. (Master of Science