EVALUATING THE INTERACTIVE ROLES OF SOIL NUTRIENTS AND POLYPLOIDY ON COMPETITIVE OUTCOMES OF CHAMERION ANGUSTIFOLIUM

Abstract

Newly formed polyploids face strong barriers preventing their establishment, but despite these barriers polyploidy is prevalent among angiosperms being a major mechanism of adaptation and speciation. Morphological and phenological differences between diploids and related polyploids often results in different ecological tolerances among cytotypes. Differences in competitive abilities brought on by genome duplication can vary with abiotic and biotic environmental conditions and influence polyploid establishment. In my theses, I test the overall hypothesis that soil nutrient availability and polyploidy interact to affect competition and performance of Fireweed plants (Chamerion angustifolium), which differ in ploidy levels. Additionally, I examined whether insect feeding damage is influenced by soil nutrient availability and polyploidy. In the first chapter, I detail a greenhouse experiment, in which I tested how soil nitrogen and ploidy level interact to affect plant competitive outcomes and performance of diploid and autotetraploid plants (cytotypes). To do this, in a greenhouse experiment, I grew cytotypes alone or with another plant of either the same or a different cytotype under low and high soil nitrogen conditions. To examine whether herbivory may affect competitive outcomes, and if soil nitrogen supply and/or ploidy level influenced insect feeding damage, we conducted a leaf-choice insect bioassay and a whole-plant insect bioassay. I found that a competitor’s ploidy level influenced plant growth traits as plants grown with tetraploids were generally smaller, but soil nitrogen availability did not differentially affect this competitive outcome. Additionally, insect damage was not influenced by competition nor soil nitrogen supplies. The second chapter details a greenhouse experiment where I examined how nitrogen and phosphorus availability and ploidy level interact to affect plant competitive outcomes and the performance of diploid, established tetraploid, and neotetraploid cytotypes. I grew the plants alone or in competition with the same or a different cytotype under low and high soil nutrient concentrations. I also conducted a leaf-choice insect bioassay and a whole-plant insect bioassay to test if competitive outcomes were affected by herbivory, and if a plant’s ploidy level and soil nutrient supplies influenced insect feeding damage. We found that whole genome duplication effects competitive outcomes and plant-herbivore interactions, but these outcomes vary depending on nutrient supply. Overall, our findings suggest that polyploids possess some traits related to competitive ability, and that these traits may have been selected for in natural populations. We conclude that soil nutrient availability plays a role in mediating the competitive outcomes between cytotypes and could be