Undergraduate Honors Theses

Thesis Defended

Fall 2015

Document Type


Type of Thesis

Departmental Honors


Ecology and Evolutionary Biology

First Advisor

William D. Bowman

Second Advisor

Barbara Demmig-Adams

Third Advisor

Abby Hickcox


Deposition of nitrogen in many areas of the world is increasing with consequences for changes in plant community and ecosystem composition and function. Mechanisms underlying these changes include nitrogen fertilization, loss of base cations (positively charged ions that regulate changes in soil pH), soil acidification, and toxicity of metal ions like aluminum. I investigated aluminum toxicity as a possible mechanism of community change in alpine ecosystems in the Front Range of Colorado. I conducted a controlled greenhouse experiment using two dominant sedge species, Kobresia myosuroides and Carex rupestris. Presence of soluble aluminum in the soil did not affect growth of either species at any level of addition. These results are unique in that other aluminum manipulation studies have shown growth of plants (especially of roots) to be inhibited at lower levels, indicating these plants are resistant to aluminum toxicity. Other mechanisms that might have influenced the observed change of cover in field plots include competition for phosphorus and water, and loss of nutrient cations from the soil. Understanding belowground mechanisms of community shifts is important to predict future changes in areas with increasing nitrogen deposition.