Date of Graduation
Eberly College of Arts and Sciences
Richard B. Thomas.
I examined the long-term effects of elevated CO2 on the leaf chemistry and photosynthesis of four species growing in the understory and two species growing in the overstory at the Duke Forest FACE experiment. I then used these measurements to parameterize a process based forest productivity model, PnET-II, in order to model the net primary productivity of the portions of the forest growing under ambient and elevated CO2. Finally, I performed a greenhouse study that examined the effects of elevated CO 2 and water availability on the growth and biomass allocation of loblolly pine seedlings from four distinct geographic locations. At the Duke FACE experiment I found a continued stimulation of photosynthesis with elevated CO2 in each species I measured. However the effect of elevated CO2 on photosynthesis of these species did depend on canopy position, season, and year. I observed no CO2-induced changes in leaf chemistry or morphology. Modeled estimates of net primary productivity of the Duke Forest were in good agreement with those measured at the Duke FACE experiment. Estimates of net primary productivity of the portions of the forest grown under elevated CO2 were much greater than the estimates of the portions of the forest grown under ambient CO2. I also found that future climatic conditions expected in North Carolina, USA should alter forest net primary productivity overall but would not alter the response of forest productivity to elevated CO2. In the study of the response of loblolly pine seedlings from different geographic locations to elevated CO2, I found significantly higher biomass in elevated CO2-grown seedlings but I found no evidence of provenance specificity in the growth response to elevated CO2. Decreased water availability did decrease the plant growth and alter biomass allocation irrespective of geographic location and growth CO2 concentration. However, I also concluded that a more detailed analysis is needed with respect to provenance specific responses of loblolly pine to variables of climate change such as CO2 and water availability. Overall my studies revealed that the stimulation of photosynthesis and productivity at the Duke Forest FACE experiment has persisted into the latter years of the experiment and, with no changes in leaf chemistry, no loss of stimulation is expected.
Springer, Clint J., "Estimating net photosynthesis and productivity of a loblolly pine forest grown with carbon dioxide enrichment" (2004). Graduate Theses, Dissertations, and Problem Reports. 2127.