Open Access Thesis
Switchgrass--Nutrition; Resorption (Physiology); Switchgrass--Variation; Switchgrass--Reproduction;
Panicum virgatum L. (switchgrass) is a bioenergy crop shown to conserve and recycle nutrients through a process known as nutrient resorption. While there are many studies looking at various aspects of nutrient cycling in switchgrass, it remains unclear whether selection is acting upon increased nutrient resorption in this species. Further, there are no phenotypic selection studies coupling empirical sexual and asexual reproduction data.
A field study and a modeling study were conducted to determine phenotypic selection on nutrient resorption and the influence of resorption on asexual reproduction in switchgrass. For the field study of phenotypic selection, I hypothesized selection favors switchgrass plants with higher rates of nutrient resorption, and furthermore selection for increased resorption is stronger in low diversity communities relative to high diversity communities because of stronger resource competition. There was mixed support for these hypotheses, as results of the field study showed marginally significant selection for increased resorption efficiency in the 16-species mixture and highly significant selection for increased resorption efficiency in the 32-species mixture. There was marginally significant selection for increased resorption proficiency in the switchgrass monoculture and highly significant selection in the 5 species mixture.
For the modeling study of asexual reproduction, I hypothesized that increased resorption would increase asexual reproduction in an environment without intraspecific variation, while an environment with intraspecific variation would lead to an optimum level of resorption relative to asexual reproduction. I also hypothesized a strong effect of increased resorption at low levels of a nitrogen gradient compared to high levels. Results supported these hypotheses, with increased resorption driving increased asexual reproduction where there is no intraspecific variation, while in the presence of intraspecific variation and competition, increased resorption resulted in increased asexual reproduction in environments with low environmental nitrogen only. These results suggest nutrient resorption is beneficial for switchgrass in terms of sexual and asexual reproduction, and that natural selection is favoring increased nutrient resorption in high diversity communities and increased terminal N concentration in low diversity communities.
Year of Submission
Master of Science
Department of Biology
Kenneth Elgersma, Chair, Thesis Committee
1 PDF file (vi, 40 pages)
©2021 Michael J. Lashbrook
Lashbrook, Michael J., "Community diversity influences selection on nutrient resorption in Panicum virgatum" (2021). Dissertations and Theses @ UNI. 1192.