The dormancy of switchgrass (Panicum virgatum L.) seeds may be broken by a variety of treatments, including after-ripening and stratification. This study was conducted to investigate and characterize more systematically factors affecting both after-ripening and stratification effectiveness, and the aging that can occur concomitantly with after-ripening. More than one year of after-ripening at ambient temperature and humidity was necessary for germination of newly harvested seeds to increase from as low as 5% to around 80%. After-ripening was not accelerated at temperatures above ambient for seeds stored in paper bags, which permitted the loss of seed moisture at the increased temperatures. Both after-ripening and aging accelerated with increases in temperature (5 to 60°C) and seed moisture content (50 to 130 g kg⁻¹), except that there was evidence of a moisture optimum for after-ripening that shifted downward as temperature increased. For many seedlots, storage at 60°C and 50 g kg⁻¹ seed moisture content for about 1 mo broke most of the dormancy and resulted in acceptably low numbers of abnormal (aged) seedlings. Decreases in germinability caused by post-stratification drying of switchgrass seeds (described herein as "reversion", in which the reverted seeds could be made germinable again by further stratification) increased as the desiccation increased. Revertibility decreased as stratification or after-ripening time increased. Stratification and after-ripening worked additively to release switchgrass seeds from dormancy. Reversion (germination with stratification minus germination after stratification followed by drying) may reveal seedlot differences and changes over time and moisture content that can not be seen otherwise. Imbibed, dormant seeds placed at 21 or 30°C were induced into deeper dormancy, as indicated by length of stratification needed to break the dormancy. Dormancy deepened more as storage temperature and time increased for imbibed seeds. There are transitional temperature and seed moisture ranges where opposing processes (aging vs. after-ripening, stratification vs. dormancy deepening) appeared to overlap or surpass one another. Switchgrass seeds, either on a single seed level, or on the population level, responded continuously to changing temperature and moisture conditions. Less aging was observed for switchgrass seeds stored in N₂. After-ripening of switchgrass seemed not to be influenced by N₂ or air. In sum, switchgrass is revealed to be remarkably plastic in its ability to move toward both greater germinability and greater dormancy. / Ph. D.

Lignocellulosic materials provide a raw material source for biofuel conversion and offer several advantages over fossil fuels- usage of a renewable resource, reduced greenhouse emissions, a decreased dependence on foreign oil, and stimulation of the agricultural sector. However, a primary technological challenge in converting lignocellulosic biomass into fuel is overcoming the recalcitrance of its matrix to enzymatic hydrolysis. To overcome these problems for chemical processing, naturally occurring cellulose biomass must be pretreated before it can be further processed using enzymatic hydrolysis or bioconversion. The goal of this work was to develop a model that predicts the glucose yield (pretreatment and enzymatic digestibility) of dilute acid pretreated switchgrass as a function of pretreatment process conditions (acid loading, 0-1.5 vol%, temperature, 165-195oC, and residence time, 1-10 min). This project was the first study that used a multivariable design experimental series to directly compare the pretreatment effectiveness (product yield, biomass composition and appearance, pH, etc) of using conventional and microwave heated reactors. Microwave-pretreated switchgrass afforded up to a 100% higher total glucose yield (combined pretreatment and enzymatic-hydrolysis liquor yields) at equivalent pretreatment severity and at one tenth of the reaction time, relative to conventional pretreatment. Under best pretreatment conditions of 0.75 vol% acid, 195oC, 1 min residence time, 99% glucose yield and 99% hemicellulose removal were achieved. Kinetic parameters were estimated for the cellulose and xylan hydrolysis reactions in the pretreatment liquor and the solid residue. The kinetic model gave an average correlation coefficient of 0.93 for all reactions. In addition, the combined severity factors (CSF) were also determined for each experiment. Highest observed enzymatic glucose yield corresponded to a CSF of 1.7. A mass and energy balance, and economic analysis based on production scale was developed for both reactor systems. The microwave pretreatment process theoretically yielded 48% more ethanol relative to the conventional process. For microwave pretreatment to be commercially viable, two criteria must be met. One, the cost for largescale continuous microwave reactors would need to be significantly lower than current estimates. And second, higher solids content must be used (>20 wt% in the slurry) to maximize output.

Selected PCB congeners (PCB 52, 77, and 153) singly and in mixtures were spiked and aged in soil microcosms and subsequently planted with switchgrass (Panicum virgatum) or poplar (Populus deltoids x nigra DN34). The planted reactors showed significantly greater reductions in PCB parent compounds when compared to unplanted systems after 32 weeks, both in single congener exposures and when all three congeners were present in a mixture. There was evidence of reductive dechlorination in both planted and unplanted systems, but higher concentrations of transformation products were observed in the planted systems than the unplanted. Although planted systems resulted in greater biotransformation, this improvement in PCB-reduction was not the result of plant uptake but rather was due to transformations occurring in the root rhizosphere. Parent PCB congeners were transformed by reductive dechlorination resulting in successively less chlorinated PCB congeners. These dechlorination products accounted for approximately all of the molar mass of parent compound lost. Based on the transformation products, reductive dechlorination pathways are proposed for rhizospheric biotransformation of PCB 52, 77, and 153. Results suggest that PCB 52 transformation proceeds through PCBs 18 and 9 down to monochlorinated PCB 1. Biotransformation of PCB 77 occurs through the intermediaries PCB 35 and 37. The pathway for the rhizospheric transformation of PCB 153 is through PCB 101 and PCB 99. This study provides insight into rhizosphere biotransformation pathways for reductive dechlorination in marginally aerobic,intermittently flooded soil as evidenced by a mass balance on transformation products. Despite the marginally aerobic conditions it is likely that highly reduced microzones existed in the soil particles during flooding and provided the opportunity for reductive dechlorination. In these experiments, planted microcosms with fully developed roots and rhizospheres showed significant reductive dechlorination and greater biotransformation than unplanted reactors. In addition, planted systems that were intermittently flooded had greater transformation of the parent PCB compounds than systems that were not. A poplar planted system resulted in the complete removal of 26 of the 29 PCB congeners detected in a commercial garden soil, while the unplanted soil only had 2 congeners completely removed after 96 days. In addition, the most recalcitrant congener, PCB 52, only decreased by 0.1% in the unplanted reactors while declining by 22.3% in the planted system. There was also greater removal of a PCB 77 spike in the planted system when compared to the unplanted system, 17.2% in the planted system versus 2.8% in the unplanted system. The results suggest that phytoremediation may be an effective tool in cleaning commercially available garden soils that are lightly contaminated with PCBs.

Biofuels have been widely recognized as a potential renewable energy source that can lessen the United States’ dependence on imported petroleum and enhance the domestic economy. Particularly, biofuels derived from lignocellulosic biomass (LCB) have been the focus in the development of a sustainable biofuels industry. However, technical barriers in the LCB feedstock supply chain have been one of the major challenges impeding the economic viability of this industry. To expedite the commercialization process of LCB-based biofuels production, this paper employed a spatial mixed-integer mathematical model to explore the optimal biomass logistic system for a switchgrass-based biofuels biorefinery in East Tennessee. The evaluated logistic systems in this study included five conventional systems (one round bale system, one square bale system, and three mixed bale systems) in the baseline scenario and one stretch-wrap bale system in the preprocessing scenario. Results showed that the stretch-wrap bale system could potentially reduce total logistic cost of switchgrass by 12 to 21% compared that of the conventional systems. Also, the result of the optimal case in the conventional systems suggested that the mixed bale system without storage protection is most economical after taking into account the dry matter loss during storage. This study also provided information regarding the optimal location of a biorefinery, a switchgrass production plan, monthly harvested and delivered tonnage, and the draw area of switchgrass under each logistic system. The optimal location of a commercial-scale biorefinery was identified to be located in the northwest of Monroe County, a location close to the demonstration plant in Venore, Tennessee. Additionally, this study showed that the percentage of available hay land used for switchgrass production, the switchgrass-ethanol conversion rate, the energy prices, and the storage dry matter loss of compact switchgrass bale produce significant impacts on the total logistic cost of switchgrass for the biorefinery.

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed on December 30, 2009). Thesis advisor: Dr. Jinglu Tan. Includes bibliographical references.

Our research investigated whether priming switchgrass seeds with water or ethephon would increase stand establishment in the field. ‘Alamo’ seed germinated faster and grew taller than ‘Cave-in-Rock.Seeds primed for six days in water or for one day in ethephon 10 mM had the greatest seedling densities. In growth chamber environments seed priming were tested to hasten germination velocity. Seeds primed for two, four or six days in water germinated faster than unprimed seeds. Ethephon treatments reduced overall germination and germination velocity. Accent and Accent Q herbicides containing nicosulfuron are used to control weeds. To test ‘Alamo’ sensitivity to these herbicides, greenhouse evaluations were conducted. Seedlings treated with Accent Q had lower shoot fresh and dry weights than Accent treated seedlings. Seedling atrazine tolerance was examined in a greenhouse study at various growth stages (1, 2 and 4 true leaves). One and two true leaf were more sensitive to herbicide damage than the 4 leaf seedlings. To investigate difference in atrazine tolerance due to differential atrazine metabolism, 14C atrazine metabolism was examined in 1, 2 and 4 leaf ‘Alamo’ seedlings. 24-48 hours after exposure, 4 leaf seedlings metabolized atrazine at a greater rate than 1 and 2 leaf stage seedlings.

Switchgrass (Panicum virgatum L.) is an important native warm-season grass for biomass and forage production in the U.S. This research determined the effect of fertilizer type (conventional, manure, and biosolids) and rate on switchgrass biomass yield and forage quality. Fertilizers were added at 0, 33, 67, 100, and 134 kg N ha-1 on established stands of ‘Kanlow’ switchgrass in three northeastern Kentucky counties. Soils across sites ranged from recently cleared forestland (low pH, P, and K) to productive cropland (high pH, P and K). Stands were sampled for forage nutritive value in June, simulating a hay harvest. Nutritive value and biomass yield were sampled in November and March. Results showed a harvest date effect for mean crude protein (CP) of 8.31% in June and 1.16% November and March. There was also a harvest effect for biomass with a mean yield of all harvests of 16.6 MT ha-1 but a N response at only one site. In conclusion, this study suggested that switchgrass may produce adequate nutritive value for dry beef cows in June and fertilizer type and rate may have a limited effect on biomass yields.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

abstract: Overall, biofuels play a significant role in future energy sourcing and deserve thorough researching and examining for their best use in achieving sustainable goals. National and state policies are supporting biofuel production as a sustainable option without a holistic view of total impacts. The analysis from this research connects to policies based on life cycle sustainability to identify other environmental impacts beyond those specified in the policy as well as ethical issues that are a concern. A Life cycle assessment (LCA) of switchgrass agriculture indicates it will be challenging to meet U.S. Renewable Fuel Standards with only switchgrass cellulosic ethanol, yet may be used for California's Low Carbon Fuel Standard. Ethical dilemmas in food supply, land conservation, and water use can be connected to biofuel production and will require evaluation as policies are created. The discussions around these ethical dilemmas should be had throughout the process of biofuel production and policy making. Earth system engineering management principles can help start the discussions and allow anthropocentric and biocentric viewpoints to be heard. / Dissertation/Thesis / Masters Thesis Civil and Environmental Engineering 2014

Grass species within South Africa show a photosynthetic subtype and phylogenetic response to rainfall gradients, with Panicoideae species (NADP-Me and NAD-Me) inhabiting mesic environments, while Aristidoideae species (NADP-Me) inhabit more arid environments. It is predicted that climate change will alter rainfall patterns within southern Africa, which could have implications for grassland distributions and functional composition. Globally, and in South Africa, species distributions indicates that NAD-Me species have a preference for more arid environments, but this may be complicated by phylogeny as most NAD-Me species belong to the Chloridoideae subfamily. Additionally, differences in the metabolism and energetic requirements of different carboxylation types are expected to confer different ecological advantages, such as drought tolerance, but the role of these different pathways is not well understood. Based on natural distribution and photosynthetic subtype differences, it was hypothesised that Panicoideae NADP-Me species would be less drought tolerant than Panicoideae NAD-Me and Aristidoideae NADP-Me species and that subtypes and lineages would show different drought recovery rates. Furthermore, drought sensitivity would be of a metabolic and not a stomatal origin and plants that maintained favourable leaf water status would be more drought tolerant and recover faster. This was tested experimentally by comparing Panicoideae species (NADP-Me and NAD-Me) and NADP-Me species (Panicoideae and Aristidoideae). Plants were subjected to a progressive 58 day drought period and a recovery phase where gas exchange, chlorophyll fluorescence and leaf water relations were measured at select intervals. In conjunction with this, a rapid drought experiment was performed on Zea mays (NADP-Me: Panicoideae) plants where similar parameters were measured. Photosynthetic drought and recovery responses showed both a subtype and phylogenetic response. Panicoideae species were less drought tolerant than Aristidoideae species, although Panicoideae NAD-Me showed better recovery rates than Panicoideae NADP-Me species, while Aristidoideae species recovered the quickest. Panicoideae NAD-Me and Aristidoideae species maintained higher leaf water status during drought which contributed to the maintenance of PSII integrity and thus facilitated rapid photosynthetic recovery. During drought Panicoideae species showed greater metabolic limitations over Aristidoideae species and for the first time, lower metabolic limitations were associated with osmotic adjustment. This is a novel finding whereby osmotic adjustment and the subsequent maintenance of leaf water are key to preventing metabolic limitations of photosynthesis in C₄ grasses. Results from the Z. mays rapid drought study showed the limitations to photosynthesis were exclusively metabolic and unlikely to be a direct consequence of turgor loss. It was apparent that the response to drought was stronger amongst lineages, as NADP-Me species from different subfamilies showed a significant difference in drought tolerances. Aristidoideae species’ exceptional drought tolerance and predicted increased aridification could favour these species over Panicoideae species under future climates.