Master of Science, University of Toledo, 2018, Biology (Ecology)

A principle driver of water-polluting harmful algal blooms (HABs) in agricultural watersheds is fertilizer phosphorus (P) runoff from farm fields. Because P is essential to plant growth, eliminating P application is infeasible. However, much of the P that is added to soils as fertilizer binds tightly to soil particles and is relatively unavailable to plants. In natural systems, microbial and faunal decomposers can increase soil P availability to plants. In agricultural systems, stimulating these organisms may help maintain P availability with decreased P application rates, thereby increasing P application efficiency while reducing runoff potential. We tested the hypothesis that stimulating soil fauna with sodium (Na+) and microbes with carbon (C) would increase soil P availability to plants. We added corn stover and Na+ solution to plots in conventionally-managed corn fields in Northwest Ohio. Stover treatments increased microbial biomass and activity and Na+ and stover combined increased soil faunal activity. However, even in both control plots and plots with stimulation of soil microbes and fauna, soil biological activity was low, and was not correlated with P availability. Therefore, in fields with low levels of decomposer activity, organisms may play a limited role in soil P cycling. In these types of ecosystems, treatments to stimulate decomposers already in those systems may be ineffective in reducing P runoff potential, at least in the short term.

Committee: Michael Weintraub PhD (Committee Chair); Daryl Moorhead PhD (Committee Member); Shannon Pelini PhD (Committee Member) Subjects: Agriculture; Ecology; Environmental Science

Doctor of Philosophy, The Ohio State University, 2017, Evolution, Ecology and Organismal Biology

The Janzen-Connell hypothesis highlights the important role of species-specific natural enemies like pathogens and herbivores in maintaining species diversity within plant communities by limiting the survival and growth of seedlings near conspecific adult plants. The extent to which natural enemies reduce conspecific seedling performance is thought to influence species richness and relative abundance within plant communities, but within-species variation in this process could also affect plant diversity at the species or population level. Variation in the strength of natural enemy effects among conspecific seedlings could occur due to factors such as the degree of relatedness between conspecific seedlings and adults (i.e., their level of shared susceptibility), or due to the characteristics of the adult that determine natural enemy accumulation (e.g., reproduction), but the causes of such variation and its consequences for patterns of plant diversity have seldom been explored. I conducted experiments with tropical tree species on Barro Colorado Island, Panama, to test new hypotheses about the causes of variation in survival and growth of conspecific seedlings near adult plants, and to examine how this variation could structure patterns of plant diversity. In Chapter 1, I conducted a shadehouse experiment with the tropical tree species Virola surinamensis to test the hypothesis that highly specialized soil microbial communities accumulate around adults within species and reduce the performance of offspring seedlings relative to non-offspring conspecifics. In Chapter 2, I conducted a field experiment with four tropical tree species to test the hypothesis that seedling performance is reduced beneath the canopies of their own parent trees than beneath those of different conspecific adults. In Chapter 3, I conducted shadehouse and field experiments with V. surinamensis to test the hypothesis that seed production reduces the performance of conspecific seedlings near f (open full item for complete abstract)

Committee: Allison Snow (Advisor); Liza Comita (Advisor); P. Enrico Bonello (Committee Member); Simon Queenborough (Committee Member) Subjects: Ecology

Bachelor of Science in Education, Ashland University, 2012, Biology/Toxicology

Different soil types display a wide range of nutrient content, microbial abundance and diversity. Many of the microbes viable in soil have practical functions in the agricultural and medical fields while others are pathogenic. Garden topsoil, potting soil, forest soil, compost and manure were the five soil types investigated in this study for bacterial abundance, species diversity, and nutrient content. We hypothesized that manure and compost would have the most nutrients and be highest in number and diversity of bacteria. Likewise, we hypothesized that potting soil would be low in all three areas. Each soil sample was diluted, plated on Plate Count Agar and incubated at 37oC for 2 days in order to maximize the number of colonies able to grow on the media. The bacteria count was determined by plate count assay and the microbial abundance by using 16S rDNA to sequence isolated species and compare the number of genera present in each soil type. A qualitative nutrient analysis was conducted to evaluate the relative nutrient content of each soil type. It was determined that the compost was richest in nitrate, phosphorus and potassium, while the other soils were low in all three. The manure exhibited a significantly higher bacterial count than all the other samples. Potting soil, compost, garden topsoil and forest soil followed with less significant variance. Similarly, the manure represented the greatest number of genera from the 16S rDNA sequencing than the other samples.

Committee: Andrew Greene PhD (Advisor); Andrew Trimble PhD (Committee Member) Subjects: Microbiology

Master of Science (MS), Wright State University, 2015, Biological Sciences

As part of the effort to understand the community structure of bacteria and archaea in groundwater fed wetlands, the vertical distribution of plant root density and species presence was studied in correlation with the change in associated bacterial and archaeal communities. Three sampling sites at a local groundwater fed wetland were selected based on surface plant community structure: Site 1 was dominated by Carex stricta, site 2 was dominated by Eleocharis erythropoda, and site 3 was dominated by a 50/50 mix of C. stricta and E. erythropoda. Core samples at 4 depths down to 1.2 m were taken to collect data on soil moisture, root density, organic matter content, plant species presence, bacteria taxa presence, and quantification of bacteria taxa. DNA sequences were used to identify plants, bacteria, and archaea. Between 13,000 – 25,000 bacterial and archaeal species are estimated to be present at each depth, with the greatest diversity found in the upper layers. Species estimates were positively correlated with soil moisture, organic content, and root mass. In total, 242 microbial classes were found with a Simpson's dominance index < 0.09, Shannon's diversity index > 3.13, and Shannon's equitability > 0.60, indicating a high diversity and somewhat even abundance. Compared to other wetlands, diversity indices are highest in wetlands with hydrology similar to fens (sub-surface vertically-flowing water). All soil parameters significantly (p < 0.05) influenced overall microbial community composition; most significantly the presence of dechlorinators, ammonia oxidizers, and methane oxidizers. Sub-surface samples revealed a greater species richness of plants than was expected from surface sampling; 22 species were found through surface survey and 25 species were found through DNA analysis. E. erythropoda (p < 0.05) significantly influenced overall changes in microbial communities. Of the 25 plants, 12 plants were correlated with specific functional groups, with at least o (open full item for complete abstract)

Committee: James Amon Ph.D. (Advisor); James Runkle Ph.D. (Committee Member); Jeffrey Peters Ph.D. (Committee Member); Silvia Newell Ph.D. (Committee Member) Subjects: Biology; Ecology; Microbiology; Plant Biology