Date of Award

Spring 1-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

William D. Bowman

Second Advisor

Noah Fierer

Third Advisor

Katharine N. Suding

Fourth Advisor

Nichole N. Barger

Fifth Advisor

Eve-Lyn Hinckley

Abstract

How plants interact with the soil around their roots is critical to how plant species function. Given the enormous ecological complexity of soils, it remains a challenge to understand the unique associations of plants and soils across plant species. Such knowledge is needed, however, to predict plant responses to changes in their environments. This work addresses questions on the theme of understanding how plant-soil interactions differ across among plant species and impact plant responses to environmental changes. More specifically, I examined how soil chemistry, nitrogen (N) availability, microbial communities, and abiotic conditions influence both plant responses to environmental change as well as plant species effects on soil microbial communities.

In three chapters I address 1) why dominant alpine sedge species shift in abundance as a result of long-term simulated N deposition, 2) a set of potential changes in environmental conditions that would promote invasion of alpine ecosystems by a non-native grass (Bromus tectorum), and 3) how variation among plant species in the same genus influences plant-soil microbial associations and plant and microbial responses to elevated N availability. Pot experiments using local plant species and their native soils in Colorado’s Front Range were used to isolate the effects of N and other factors on plant- soil associations. I found that 1) alpine sedges, Kobresia myosuroides and Carex rupestris, are not changing in abundance due to N induced shifts in bacterial composition or exposure to soluble aluminum. However, ectomycorrhizal fungi may play a role in shifts in sedge abundance with N addition. Alpine invasion 2) by Bromus tectorum would likely be inhibited by alpine soil, while the beneficial effects of increasing growing season temperatures and N deposition could promote growth of lower elevation populations. Finally, 3) congeneric Poa species have unique effects on soil fungal community composition but not bacteria composition, and N addition enhanced the unique effects of plant species for both fungi and bacteria. Together, these results demonstrate how soils contribute to variation in plant species’ responses to environmental change and plant species’ effects on soil microbial communities.

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