Undergraduate Honors Theses

Thesis Defended

Spring 2016

Document Type


Type of Thesis

Departmental Honors


Ecology and Evolutionary Biology

First Advisor

Barbara Demmig-Adams

Second Advisor

Pieter Johnson

Third Advisor

James White


Rising atmospheric carbon dioxide (CO2) concentrations are associated with rising global temperatures; these changes alter ecological communities in ways that vary among plant species and environmental conditions. Research on the response of various plant species to elevated CO2 concentration is needed to predict future implications of climate change on ecosystems. Free-Air-CO2 Enrichment (FACE) experiments examine the effects of elevated atmospheric CO2 levels on terrestrial ecosystems by manipulating atmospheric CO2 concentration of native vegetation.

The present study was the first ever FACE experiment in a mature Australian Eucalyptus woodland and simulated an ecosystem exposed to CO2 levels of 550 parts per million (ppm), which is the projected global atmospheric CO2 concentration for 2050. Control plots were exposed to un-manipulated atmospheric CO2 levels of approximately 400 ppm. The influence of elevated atmospheric CO2 on the ecosystem was assessed by analyzing photosynthesis rates, radial tree growth (trunk circumference and calculated stem-basal area growth), and photosynthetic water-use efficiency (the ratio of photosynthetic CO2 uptake to transpirational water loss). This approach led to three major findings: elevated CO2 (1) caused photosynthesis to be modestly (2.7%), albeit significantly, higher, (2) did not have an effect on radial tree growth, and (3) was associated with a significantly lower stomatal conductance and greater photosynthetic water-use efficiency. The results of this study are discussed in the context of plant-species-specific differences in the response to elevated CO2 and elevated temperatures at the ecosystem level.