Thesis (Ph. D.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 223-241).

Afforestation and reforestation programs utilizing available fields for biofuel production, carbon sequestration, and other uses linked to climate change are looking to tree physiologists to identify species and genotypes best-suited to their purposes. The ideal poplar genotype for use in Canadian programs would be drought-resistant, cold-climate adapted, and fast-growing, thus requiring an understanding of links between a variety of physiological traits linked to growth and productivity. This study examined the basis for variations in water-use efficiency within four selected populations of Populus trichocarpa and Populus balsamifera (2 provenances each). Each species included both a northern and a southern provenance. Correlations between water-use efficiency, nitrogen-use efficiency, ¹³C/¹²C isotope ratio, stomatal conductance, and overall productivity were evaluated. Gas exchange variables measured included net photosynthesis, transpiration rate, stomatal conductance, and intercellular CO₂ content. Water-use efficiency and ¹³C content across all genotypes were highly correlated. Results suggested that variation in water-use efficiency was primarily related to variation in stomatal conductance across all genotypes. Whereas differences in net photosynthesis in this study were not significant between species, P. balsamifera did reveal a higher average stem volume overall. Although variation in stomatal conductance was the major determinant of differences in water-use efficiency, positive correlations were found between ¹³C isotope abundance and net photosynthesis in both P. balsamifera provenances. In this regard, results for the northern P. balsamifera provenance are the most consistent across all gas-exchange and growth trait correlations, in terms of meeting expectations for sink-driven water-use efficiency. The findings in this study suggest the possibility of identifying poplar genotypes with an absence of trade-off between water-use efficiency and nitrogen-use efficiency, notably among genotypes from the northern P. balsamifera provenance, near Gillam. / Forestry, Faculty of / Graduate

Trichloroethylene (TCE) was widely used as an industrial solvent and degreasing agent for most of the twentieth century. It is now a widespread groundwater contaminant. Phytoremediation may be a cost-effective cleanup method for TCEii contaminated soils and groundwater. Studies of environmental TCE fate are complicated by its volatility. The literature repons both significant and insignificant plant uptake of TCE. Conflicting findings may be due to differences in exposure level, conditions, and duration of the studies, or to experimental artifacts from laboratory systems. This research quantified plant uptake and volatilization of TCE using a unique laboratory system. Hybrid poplar trees were exposed to 1 or 10 ppm TCE over a 43-d period. [14C]TCE was added to four high-flow, aerated, hydroponic plant growth chamber systems designed to provide high mass recoveries, an optimal plant environment and complete separation between foliar and root uptake. Transpiration stream concentration factors (TSCFs) for TCE, calculated from total [14C]TCE in shoot tissues plus phytovolatilized 14C, were 0.11 for two 1 ppm treatments and 0.15 for a 10 ppm treatment with roughly 25% attributed to phytovolatilization. Though extending study duration from 26 to 43 d resulted in accumulation of more mass of 14C in plant tissues, it had no effect on TSCF. These TSCF values are much lower than other published experimental values and values predicted by a theoretical relationship between TSCF and octanol-water partition coefficient. The TCE metabolites trichloroethanol (TCEt), trichloroacetic acid (TCAA), and dichloroacetic acid (DCAA)were identified in plant tissues of the 10-mg/L treatment. Hybrid poplar uptake ofTCAA and TCEt was quantified using a simpler aerated hydroponic system. TSCF values were calculated based on extractable parent compound in shoot tiss ues. TSCF for TCEt was < 0.01. Presence of TCAA in hydroponic solution and in leaf and root tissues indicated transformation of TCEt to TCAA. TSCF for TCAA was < 0.03 and decreased with increasing exposure concentration. TSCF also decreased under oxygen-limited root-zone conditions. Presence of DCAA in leaf and root tissues indicated transformation ofTCAA to DCAA. Transformation of parent compound, coupled with low extractability, may contribute to low TSCFs.

Short rotation woody crops (SRWC) eastern cottonwood (Populus deltoides) and hybrid poplar plantations were established in 2021 in Pontotoc and Oktibbeha counties of Mississippi to study the biomass potential of SRWC for biofuel production. We used a novel backpack LiDAR system to measure forest metrics and harvested sample trees to build aboveground biomass (AGB) and leaf area index (LAI) equations. The results showed that LiDAR-derived variables accurately estimated aboveground biomass (R2 =0.81 and 29.22 % RMSE). However, the LAI estimation results showed that the LiDAR metrics moderately explained field measurements of LAI (R2 =0.31 and 18.05% RMSE) for individual-trees and poorly explained plot-level LAI measured with the LAI-2200C (R2 =0.11 and 66% RMSE). The backpack LiDAR system can be valuable for forest managers and researchers, enabling non-destructive AGB and LAI estimation. However, further research is required to overcome its limitations and achieve precise measurements of AGB and LAI.

This study aimed to evaluate the physical and mechanical properties of red oak (Quercus spp.), white oak (Quercus spp.), hard maple (Acer saccharum) and yellow-poplar (Liriodendron tulipifera) and compare them to values from past publications. Mechanical testing was conducted on small, clear, defectree specimens from red oak, white oak, hard maple and yellow-poplar following the standard ASTM D143. Percentage of latewood, moisture content, specific gravity, modulus of elasticity (MOE), modulus of rupture (MOR), compression parallel and perpendicular to the grain and Janka hardness were determined. Results indicated that mechanical properties for red oak, white oak, hard maple and yellow poplar have not changed substantially because the average values remain in a range that is very close to the ones published in past studies. Thus, values from the Wood Handbook can still be used for engineering purposes.

Species in the genus Populus (poplars) have shown the potential to be utilized as short rotation woody crops for bioenergy production in the Southeast. A lack of knowledge on which poplar taxa perform best on marginal sites throughout the Southeast exists. Through measurement of relationships between growth metrics, water usage and physiological parameters of 2400 poplar trees, I was able to assess: 1) early rotation suitability of numerous poplar varietals to be grown as bioenergy feedstocks in northeast Mississippi, and 2) the effectiveness of early rotation physiological parameters in predicting future productivity and water usage. Overall findings from this study suggest that trees with D x M parentage may be best fit for large-scale plantation growth in the Southeast. They demonstrated low mortality and collectively grew the tallest of all taxa. Early-rotation physiology demonstrated mixed results in predicting future growth and water usage. Findings from this study will be used in future bioenergy feedstock selection.

No description available.

A computer program was developed which provides the necessary information required by landowners to evaluate thinning alternatives in yellow-poplar stands. The program is written Applesoft BASIC for the APPLE II+ microcomputer with a design which emphasizes flexibility and ease of use. The program consists of two primary segments: growth and yield, and economic evaluation. The growth and yield segment is composed of a stand level growth and yield model which consists primarily of a collection of equations specified by Knoebel (1982). The economic evaluation segment calculates two measures of economic performance for before or after taxes. The performance criteria are the present net worth and internal rate of return. Using the computer program developed in the study, optimum thinning regimes were estimated for existing stands of yellow-poplar under a variety of economic and biological conditions. Given a set of benchmark costs and revenues, optimum thinning regimes were estimated for three sites (80, 100, and 120, base age 50). A sensitivity analysis was conducted in which interest rates, thinning costs, and clearcut stumpage values were varied. The optimum regimes expressed varying degrees of sensitivity to changes in the economic parameters. / M.S.

Ten strategically placed push-pull wells were installed to determine in-situ degradation rates at a creosote contaminated site and to assess the contribution of hybrid poplar trees to polynuclear aromatic hydrocarbon (PAH) remediation. Well positioning enabled comparison between contaminated and non-contaminated locations, as well as comparisons between locations with and without trees. Comparison of areas with and without trees enabled an improved understanding of the role that the phytoremediation system has on the overall degradation of PAHs at the site. Bromide, a conservative, non-reactive tracer, was injected in solution along with dissolved oxygen. Twelve push-pull tests (PPTs) were performed, of which three did not include naphthalene in the injection solution, so that the developed method could be evaluated, tested, and yield an initial set of rates to make seasonal and spatial varying in-situ comparisons. Method comparison used for rate analysis found the highest confidence in the method of Snodgrass and Kitanidis (1998) for zero order rates and the method of Haggerty et al. (1998) for first order rates. The largest zero and first order rates, 2.43 mgnaphthalene/L-hr and 1.25 1/hr, respectively, occurred at treed regions in June. Zero and first order winter rates at treed regions were greater by a factor of at least 2.5 when compared to non-treed regions. Degradation rates at treed regions were found to steadily increase by over four times from winter to summer. Results validate that decay variations attributed to phytoremediation can be detected with the push-pull method. PPTs performed at the Oneida site verified observed trends determined from six years of monitoring data, microbial characterization, and microcosm studies. / Master of Science

Direct transpiration rates and plant uptake of naphthalene by a hybrid poplar phytoremediation system located in Oneida, Tennessee were determined using hydrologic and groundwater concentration data. Water table recession analysis techniques were employed to determine direct transpiration rates from the saturated zone of the shallow, unconfined aquifer underlying the site. Direct transpiration rates varied over the growing season (late March to mid-October), with a maximum and mean daily direct transpiration of 0.0100 and 0.0048 feet/day, respectively. During 2004, the maximum direct transpiration rate was observed in May, and rates declined starting in June due to an associated decline in the water table. A technique was developed to estimate the volumetric transpiration rate of each tree based on the breast-height diameters and seasonally variable direct transpiration rates. During peak transpiration, the larger trees at the study site were estimated to directly transpire 4 to 13 gallons per day per tree. Plant uptake rates of naphthalene were estimated by superimposing spatial data (volumetric transpiration rates and naphthalene concentration in groundwater). The mass loss rate of naphthalene from the aquifer as a result of plant uptake during July 2004 was 335 mg/day which only represents 0.117% of the aqueous mass plume. Monthly groundwater profiles showed a decrease of the saturated thickness beneath the system of hybrid poplars between the dormant and active season. This study suggests direct transpiration rates and plant uptake of naphthalene are dependent on variables including climatic parameters, magnitude of the saturated thickness, and the concentration of naphthalene in groundwater. / Master of Science