Mycorrhizal fungi are soil-borne organisms that form symbiotic associations with the majority of land plants. These fungi gather and exchange mineral nutrients with plants for photosynthetically derived carbohydrates. Mycorrhizal fungi can also confer other benefits onto plants, e.g. defense against pathogens, improved water relations, tolerance to heavy metal toxicity and herbivory. The influence of mycorrhizal fungi on plant mineral nutrition and response to stress suggests that these organisms may have a role to play sustainable agriculture as well as in bioremediation and ecosystem restoration. In contributing to this important research, I investigated host-specific interactions between mycorrhizal fungi and the sex morphs of the gynodioecious perennial herb Polemonium foliosissimum (Polemoniaceae) and their mycorrhizal associates in the field. I hypothesized that the genders of this species differed in their associations with mycorrhizal fungi in benefits received. I performed a full factorial simulated herbivory experiment and evaluated the extent of mycorrhizal colonization in the roots as well as the concentrations of nutrients in leaf tissue. Mycorrhizal colonization and leaf nutrient concentrations did not differ between the genders nor were influenced by the experimental treatments. This suggests that the genders of Polemonium foliosissimum do not interact differently with mycorrhizal fungi, and thus do not represent different "hosts". Also, I investigated local adaptation of mycorrhizal associations by exploring the effect of large herbivore grazing on plant-mycorrhizal associations. I hypothesized that grazing by large herbivores results in locally adapted symbioses that enhance plant response to herbivory. I grew the perennial bunchgrass Themeda triandra (Poaceae) in inoculum prepared from soils collected from three field exclosures with differing histories of large herbivore exclusion in the Kenya Long Term Exclosure Experiment. I conducted a full factorial simulated herbivory experiment in which plants were subject to two clipping events over the course of 5-months, and evaluated plant regrowth as well as mycorrhizal colonization for plants in the experiment. Plants grown in inoculum from exclosures in which large herbivores have had access produced more root mass when mycorrhizal fungi were present. Further, I found equivalent biomass production of clipped and non-clipped plants in inoculum prepared from the exclosure with only native large herbivore access while equivalent biomass production was not found in the substrate prepared from areas with a history of large herbivore exclusion. This suggests that mycorrhizal fungi mediate plant growth and response to herbivory in this system.

This thesis explores the seed germination of seven wildflowers native to sub-alpine ecosystems. Wildflowers are an essential functional group in native plant ecosystems. Also known as forbs, these plants offer a myriad of benefits in addition to being aesthetically pleasing. They provide habitats for anthropods and small mammals, support native pollinator populations, and grow well with other plant functional groups (especially perennial grasses and shrubs). Healthy plant communities make use of the limited resources in our native ecosystems, competing with invasive species that can otherwise dominate the landscape. Germination involves the transition from seed to an actively growing plant. Following germination, the seedling relies on stored energy reserves until it becomes as an autotrophic organism. Because germination is irreversible, it is the most vulnerable period of the plant lifecycle. Seeds of sub-alpine plants typically have complex dormancy-breaking requirements before growth begins. Therefore, understanding factors that influence the germination is essential to understanding propagation for horticultural use as well as timing of seedings for ecological restoration. The first chapter investigates the germination behavior of two co-occurring Asteraceae species across an elevation gradient. Mules ear (Wyethia amplexicaulis) and arrowleaf balsamroot (Balsamorhiza sagittata) seeds were collected at low, mid, and high elevation locations then subjected to a number of cold stratification treatment lengths (4-20 weeks) Both showed variance in germination behavior between elevation collection locations, with higher locations exhibiting a longer stratification requirement. The second study was developed to determine methods for breaking dormancy in five wildflower species for which existing literature is nonexistent or lacking. Delphinium nuttalianum (low larkspur), Delphinium exaltatum (tall larkspur), Frasera speciosa (green gentian), Polemonium foliosissimum var. alpinum (Jacob's ladder), and Mimulus grandifloras (monkey flower) were selected for this study because they all have the potential for use in horticulture and restoration ecology applications. Three species (low larkspur, tall larkspur, and green gentian) required long-term cold stratification to break dormancy. Jacob's ladder required physical scarification to break dormancy, and monkey flower required the combination of constant temperature with light exposure to germinate. These findings indicate that 1) six of seven species should be autumn-planted, and that propagation for horticulture use for five of the species is a lengthy process involving several months; 2) propagation of monkey flower seeds include strict temperature and light requirements; and 3) while seeds collected from different locations have the same type of dormancy-breaking requirements, variation in the degree of seed dormancy has ecological relevance.