Date of Graduation

2008

Document Type

Thesis

Degree Type

MS

Committee Chair

Richard B. Thomas

Abstract

Forested ecosystems are the largest terrestrial sinks for carbon dioxide (CO2) on earth and are important in mitigating the negative effects of human induced increases of atmospheric CO2. Trees fix CO2 into sugars by using the nitrogen demanding processes of photosynthesis. Modeling and empirical studies have shown stimulations in photosynthesis under elevated CO2 conditions but the response decreases as plant demand for N increases. I examined the interaction of CO2 and N on photosynthetic capacity of Liquidambar styraciflua trees growing in the overstory and four deciduous hardwood species, including Acer rubrum, Carya glabra, Ulmus alata, and Liquidambar styraciflua, in the understory at the Duke Free Air CO2 Enrichment (FACE) experiment. Photosynthesis of overstory sweetgum trees all four understory species responded positively to elevated CO2 despite low N availability. However, there were differences in the stimulation of photosynthesis by each species such that Acer rubrum had a 57% stimulation and Liquidambar styraciflua and Carya glabra had 49% and 39% stimulation, respectively. Leaf physiological parameters of these three species were unaffected by elevated CO2 and showed no negative responses to low N availability. However, the understory species, Ulmus alata, growing with elevated CO2 had a 20% reduction in carboxylation rate and a 12% reduction in foliar Narea suggesting the onset of photosynthetic down regulation. Ulmus alata also had the lowest (25%) stimulation in photosynthesis under elevated CO2. These results show some species may have a competitive advantage over others in the future forests of North Carolina; which could lead to changes in species composition and eventually forest ecosystem function.

Download

Share

COinS