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Three studies were conducted to determine the effects of ozone, water stress, and simulated acidic rain on the growth and physiology of Fraser fir seedlings. In Experiment I, seedlings were first exposed to 2 levels of moisture stress conditioning (MSC) for four weeks, and 3 levels of ozone ( < 0.02, 0.05, and 0.10 ppm) and three levels of water stress (control, moderate, and severe) for 10 wks. The 2 MSC levels were a control (well-watered at all times) and a stress treatment in which seedlings were not watered until pre-dawn needle water potential measurements ('I') fell below -1.0 MPa. The 3 levels of water stress were a control (well-watered at all times); a moderately stressed treatment (seedlings watered when 'I' levels fell between -0.8 and -1.0 MPa); and a severely stressed treatment (seedlings watered when 'I' fell below -1.2 MPa). Fraser fir seedlings were exposed to 3 levels of simulated rain (pH 3.0, 4.3, and 5.6) and 2 levels of ozone ( < 0.02 and 0.10 ppm) in Experiment II for 10 wks. Fraser fir seedlings in Experiment III were exposed to ozone levels of < 0.02, 0.05, and 0.10 ppm ozone and control, moderate, and severe water stress (as specified above) for 10 wks during the first year. Seedlings were then exposed to 2 levels of ozone ( < 0.02 and 0.10 ppm) for 10 wks in the following year. Analysis of data indicate that ozone of 0.10 ppm significantly decreased net photosynthesis (Pn) in one study but was not significant in reducing Pn in the other two studies. Ozone also failed to reduce growth significantly; however, decreasing trends were often apparent. Fraser fir biomass, transpiration (Ts), and needle conductance (Cs) were significantly decreased by water stress. Water-use efficiency was also improved as a result of prior moisture stress. Simulated acidic rain did not result in any significant changes in biomass accumulation, height, or diameter increment over the ten week period of the study. A solution of pH 3.0 did result in significantly higher root surface area and significantly reduced Ts after 5 wks of exposure; these responses are possibly due to a fertilization effect. No treatment interactions were significant. However, the combined, cumulative effect of all of these stresses may contribute to an overall decline in forest ecosystem productivity. / Master of Science

Precipitation over the eastern United States has been increasing in acidity, particularly within the last three decades. The average annual pH of rain in this area is about 4.2. The foliar surface, or phylloplane, of soybean can be damaged by rain acidified to pH 2.9. Simulated acidic precipitation has an overall inhibitory influence on soil microbial processes. The effect acidic precipitation may have on epiphytic microorganisms has not been examined. Bacteria are among the most numerous residents on the phylloplane. / Master of Science

One-year-old seedlings of red spruce, loblolly pine, yellow-poplar, and sweetgum were exposed to ozone (0.0 or 0.1 ppm, 4 hr d⁻¹, 3 d wk⁻¹) in combination with simulated acidic rain (pH 5.6 or 3.0, 1 h d⁻¹, 2 d wk⁻¹, 0.75 cm hr⁻¹) for ten weeks. After the ten-week treatment with ozone and simulated acidic rain, the seedlings were submitted to two drought cycles, and water potential, net photosynthesis (Pn), stomatal conductance (Cs), and transpiration (Ts) were measured. Whole-plant fresh weight increment (FWT) and dry weight were significantly reduced in red spruce seedlings after the ten-week treatment with ozone. Ozone also significantly reduced shoot height growth (SHG) and increased the apparent plastochron duration (APD) of sweetgum seedlings. Treatment with simulated rain at pH 3.0 significantly increased FWT and SHG of red spruce compared to pH 5.6 as well as FWT and relative growth rate (RGR) of loblolly pine. The APD was significantly reduced in sweetgum seedlings exposed to simulated acid rain at pH 3.0 compared to 5.6. Significant interactions between ozone and simulated acidic rain occurred in all species except red spruce, and they were additive. The SHG was significantly lower in loblolly seedlings exposed to 0.1 ppm ozone + pH 5.6 than in seedlings exposed to either 0.1 ppm ozone + pH 3.0 or 0.0 ppm ozone + pH 5.6. The APD was significantly increased in yellow-poplar and sweetgum seedlings exposed to 0.1 ppm ozone + pH 5.6 compared to any other treatment. Visible symptoms appeared on the adaxial leaf surface of yellow-poplar seedlings submitted to acid rain at pH 3.0 regardless of ozone treatment. Visible foliar symptoms were also observed on the adaxial surface of sweetgum seedlings exposed to 0.1 ppm ozone. The symptoms were characterized by premature red pigmentation with small brown necrotic lesions. Foliar concentrations of P and S were significantly increased in all seedlings exposed to simulated rain at pH 3.0 compared with pH 5.6 except for red spruce which exhibited the increases of K and S. In general, there were neither significant effects of ozone nor interactions between ozone and rain pH on foliar nutrient concentrations. There were no significant effects of ozone on Pn, Cs, Ts, or water-use efficiency (WUE) prior to the drought cycles for all species. However, after the first drought cycle, Pn and Cs were significantly changed in loblolly pine and sweetgum pre-exposed to 0.1 ppm ozone compared with controls. The ten-week treatment of simulated acidic rain at pH 3.0 significantly increased Pn and Ts of loblolly pine and reduced Cs of yellow-poplar. After the first drought cycle, yellow-poplar treated with pH 3.0 rain showed lower Pn and WUE than seedlings exposed to pH 5.6 solution. A 0.5 MPa shift in the response of net photosynthesis (Pn) to decreasing water potential occurred in red spruce seedlings across all air pollutant treatments after the drought cycles indicating photosynthetic acclimation to drought stress. During the second drought cycle, Pn was more sensitive to water potential in red spruce and loblolly pine seedlings exposed to 0.10 ppm ozone + pH 3.0 solution compared with seedlings exposed to 0.0 ppm ozone + pH 5.6 solution. This increased sensitivity of Pn to water potential might be explained through a change in root hydraulic conductivity (Lp). In general, Lp showed significant effects of ozone and simulated acidic rain after moisture stress. After the first drought cycle, Lp was decreased in yellow-poplar and sweetgum seedlings exposed to 0.10 ppm ozone. After the second drought cycle, Lp was decreased in yellow-poplar and red spruce seedlings exposed to 0.1 ppm ozone. Significant interactions between ozone and simulated acidic rain occurred in the Lp of red spruce and yellow-poplar seedlings after the first drought cycle. The results from this dissertation indicate that ozone and/or simulated acidic rain can alter the growth and drought susceptibility of forest tree species under laboratory conditions. Forest trees which are periodically exposed to ambient ozone and acidic rain in natural forest ecosystems probably have a response similar to the results from this study. Additional research is necessary to determine if such effects are occurring in natural forest ecosystems. / Ph. D.

Master of Arts / Department of Economics / Tracy M. Turner / The report examines the extent to which the United States market for tradable pollution permits has been an efficient way to reduce sulfur dioxide emissions from coal-burning power plants. To do so, this report first provides background information on the effects of SO2 emissions on the environment in the United States. It discusses the initial attempt with the 1970 Clean Air Act to reduce these emissions and its degree of success. The details of the 1990 Amendments are then given. The economic theory behind the different methods of pollution control (quantity regulation, technology mandate, taxation, and emissions restriction through tradable permits) is explained and their efficiency regarding consumer and producer surplus is contrasted. The report then reviews published articles regarding the topic at hand. The U.S. Acid Rain Program has been found to be very efficient in its ability to reduce sulfur dioxide emissions at a low cost to the producers.

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