Kendig, Amy2018-03-142018-03-142017-12https://hdl.handle.net/11299/194591University of Minnesota Ph.D. dissertation.December 2017. Major: Ecology, Evolution and Behavior. Advisors: Eric Seabloom, Elizabeth Borer. 1 computer file (PDF); viii, 129 pages.Human activities and management choices can impact the spread and intensity of diseases in plant and animal populations. For example, high nutrient inputs to terrestrial and aquatic systems may enhance pathogen success or aid hosts in resisting and tolerating disease. Because nutrient supply rates and ratios mediate interactions among free-living species, they may also influence interactions between hosts and pathogens. Further, it is increasingly clear that infections involve multiple different kinds of pathogens, and their interactions may also be mediated by environmental nutrients. The goal of my dissertation research was to understand how soil nutrients affect interactions among plant viruses and the consequences of these interactions for disease dynamics. We used field-collected data to determine how nutrients, among other factors, affected spatial patterns of viruses in grasslands. We found that virus pairs frequently co-occurred, and phosphorus (P) addition promoted the aggregation of one pair. Then, we performed growth chamber experiments to evaluate how nitrogen (N) and P mediated within-host interactions between two viruses, disease severity, and transmission to new hosts. We found that pathogens coexisted within hosts and occasionally benefitted from increased N. Disease severity was not strongly influenced by soil nutrients, but modeling results indicated that this outcome depended on the mechanism behind virulence. Finally, we found that the viruses were likely to coexist at the host population scale, despite inhibition that occurred during transmission. These results indicate that soil N and P influence some aspects of the system, but are not the main drivers behind virus diversity. This research contributes to a growing body of knowledge about the mechanisms linking environmental nutrients to disease across systems.enbarley and cereal yellow dwarf virusesdisease ecologynitrogenphosphorusThesis or Dissertation