The position of newly expanded shoot leaves in the canopy of apple trees had significant and similar effects on specific leaf weight (SLW), leaf thickness, length of palisade tissue, and number of cell layers in the palisade tissue. Inside canopy leaves had lower SLW, leaf thickness, palisade length, and number of palisade cell layers than middle and outside leaves at each of six sample dates ranging from late May to early October. Outside canopy leaves had the highest values at all sample dates. Differences in SLW, leaf thickness, and palisade length between inside and outside leaves increased as the season progressed, primarily due to a general increasing trend in outside leaves that developed later in the season. Effects of canopy position on spur leaves were not as great as with shoot leaves. Regression analysis showed SLW to be significantly correlated with leaf thickness and palisade length. / M.S.

Changes in light harvesting ability and other physiological responses could int1uence the competitive outcomes of tree species in a future elevated CO₂ atmosphere. Photosynthetic light response curves were constructed with a closed photosynthesis system (LI-COR, Inc. Lincoln, NB) in order to investigate the effect of growth in elevated CO₂ (746 μl⁻¹) and ambient CO₂ (379 μl⁻¹) on light responses, and seedlings were allowed to dry out to examine physiological changes to water stress. While drying out, photosynthesis was measured with a closed system (LI-COR, Inc. Lincoln, NB) and fluorescence was measured with a portable fluorescence measurement system (P.K. Morgan Instruments, Inc Andover, MA). No species showed significant increases In quantum yields or decreases in light-compensation points as a result of elevated CO₂. Photosynthesis declined in all species due to water but seedlings grown in elevated C0₂ maintained photosynthesis longer. Loblolly pine and red maple grown in e1evated CO₂ showed signs of photosynthetic acclimation. Photochemical efficiency of PSII declined with water stress in loblolly pine. Red maple and sweetgum showed no relationship between photochemical efficiency of PSII and simulated drought. Growth in elevated C0₂ did not influence this response in loblolly pine, but sweetgum started with a lower photochemical efficiency or PSII which increased significantly. / Master of Science

Varietal forestry may increase the productivity of loblolly pine (Pinus taeda L.) in the Southern United Sates. However, the effects of these genetic x environment interactions are still poorly understood. In this study we examined the responses in growth, stand uniformity and leaf level physiology of loblolly pine clonal varieties and families to silvicultural intensity and site effects. We also looked for patterns in observed traits that were consistent between crown ideotypes. Two varieties of each crown ideotype (narrow vs broad crowns) and two families (controlled mass pollinated (CMP) and open pollinated (OP) family) were tested on the Virginia Piedmont (VA) and the North Carolina Coastal Plain (NC) under different silvicultural intensities (operational vs intensive), and planting density (617, 1235 and 1852 trees per hectare). Data were collected during the first four growing season after establishment. At NC, intensive silviculture increased crown-width, height and dbh by 33%, 14%, and 23%, respectively. At VA, intensive silviculture increased crown-width, height and dbh by 41%, 10%, and 23%, respectively. Intensive silviculture also increased slightly but significantly the stand uniformity of stem growth. However, the differences in productivity between silvicultural treatments were not explained by differences in leaf-level physiology. Across all treatments and sites the varieties generally grew faster than the OP family, but the differences were higher at VA. Varieties did not differ in stem growth, but the broadest crown variety had greater stand uniformity, photosynthetic rate (Asat), carbon isotope discrimination (∆¹³) and lower fascicle size than the OP family. None of the traits assessed inthis study was consistent within the ideotypes. Varieties classified in the same crown-ideotypes may respond differently to the environmental effects of site and silviculture, which reinforces the need of matching varietal forestry with precision silviculture to achieve gains in productivity. / Ph. D.

To decrease dependency of fossil fuels and avoid direct competition with food crops, massive research efforts are investigating next-generation cellulose biofuel crops such as switchgrass (Panicum virgatum). A low-input, sustainable switchgrass production could be achieved by reducing traditional management practices though applying plant growth promoting rhizobacteria (PGPR), of which our understanding is still rather limited. To elucidate physiological mechanisms behind PGPR's beneficial effects, we inoculated switchgrass seedlings with Burkholderia phytofirmans strain PsJN. Two experiments were conducted to determine the initial and long-term responses of switchgrass to PsJN inoculation by tracking growth and leaf physiology. In a third experiments, we tested the effects of PsJN on growth and leaf-level physiology of switchgrass under a moderate pre-drought conditioning and a successive severe drought stress. PsJN inoculation increased biomass and promoted elongation of shoots within 17 days following inoculation. The enhanced root growth in PsJN inoculated plants lagged behind the shoot response, resulting in greater allocation to aboveground growth (p=0.0041). Lower specific root length (p=0.0158) and higher specific leaf weight (p=0.0029) were also observed in PsJN inoculated seedlings, indicating advanced development. Photosynthetic rates (Ps) were higher in PsJN inoculated seedlings after 17 days (54%, p=0.0016), which were related to higher stomatal conductance, greater water use efficiency, and lower non-stomatal limitation of Ps. These rapid changes in leaf physiology are at least partially responsible for switchgrass growth enhancement from PsJN treatment. The early growth enhancement in PsJN inoculated switchgrass linearly decreased with plant age. PsJN inoculation increased Ps of upper canopy leaves by 13.6% but reduced Ps of lower canopy leaves by 8.2%. Accelerated leaf senescence and early flowering were observed in PsJN-inoculated switchgrass, which might contribute to slightly lower aboveground biomass at final harvesting. Drought preconditioning increased Ps of PsJN-inoculated switchgrass during a later severe drought; whereas, control switchgrass only benefited from drought preconditioning when leaf water potential dropped below -1 MPa. This study verified early growth enhancement and accelerated development of switchgrass due to PsJN inoculation. Rapid improvement in leaf physiology is related to enhanced productivity. PsJN inoculation also improve drought tolerance of switchgrass. / Ph. D.

This dissertation research work focuses on the investigation of novel donor-acceptor systems elucidating their photochemical properties, anion binding, and their potential application in the development of artificial photosynthetic systems. The explored systems are based on oxoporphyrinogen (OxPs), porphyrins, fullerene, and boron dipyrromethene (BODIPY) based donor-acceptor systems. The photochemical properties of novel molecular systems were elucidated using UV-vis spectroscopy, fluorescence spectroscopy, electrochemical methods, computational calculations, and ultrafast transient absorption spectroscopy. A novel BODIPY-oxoporphyrinogen dyad which is able to bind with fluoride anion promoting the excited state ultrafast electron and energy transfer events mimicking the primary events in natural photosynthesis was introduced. Further, self-assembly of supramolecular complexes based on oxoporphyrinogens, fullerene, and different zinc porphyrin dimers was explored. The formed self-assembled complexes have shown photoinduced electron transfer. A novel push-pull supramolecular construct based on the spiro-locked N-heterocycle-fused zinc porphyrin was studied. The excited state charge separation and stabilization of this push-pull system was enhanced by the complexation with fluoride anion. Also, the effect of BODIPY functionalization and linkers on the electron transfer properties of a series of carbazole–BODIPY and phenothiazine-BODIPY dyads were investigated. These findings are important to develop advanced and efficient BODIPY-based donor-acceptor systems for efficient light harvesting applications. The entire study aims to expand our understanding of these systems and contribute towards the advancement of sustainable energy technologies.

In this Ph.D. thesis I am dealing with the effect of dynamic irradiance on (i) photosynthesis, growth and bundle sheath leakiness (for CO2) of C4 plants and (ii) bryophyte photosynthesis. Part of this thesis is literature review on broader aspects of the dynamic light effects on photosynthetic and growth processes in plants.

Indiana University-Purdue University Indianapolis (IUPUI) / Carbon dioxide (CO2) level in the atmosphere has increased steadily since Pre-Industrial times. The need for a better understanding of the effects of elevated CO2 on plant physiology and growth is clear. Previous studies have focused on how plants are affected by either elevated CO2 or salinity, one of many environmental stresses for plants. However, little research has been focused on the interaction of these two factors. In my project, three common grass species were exposed to both elevated CO2 and salinity, so that the effects of either of these factors and the interaction of the two on these species could be examined. The CO2 levels were set to 400 µmol mol-1, close to the current concentration, or 760 µmol mol-1, projected to be reached by the end of this century. Salt solutions of 0, 25, 50, 75, and 100 mM NaCl with CaCl2 at lower rates (1% of each respective molarity for NaCl) were used to water the grasses, which are unlikely to experience prolonged exposure to salt conditions beyond this range in their natural habitats. The three common grass species studied in my experiment were Kentucky bluegrass (Poa pratensis L.) and red fescue (Festuca rubra L.), both C3 cool season grasses, as well as buffalo grass (Buchloe dactyloides (Nutt.) Engelm.), a C4 warm season grass. Each treatment had five replicates, bringing the total number of experimental pots to 150. Various growth parameters were monitored, and all data was statistically analyzed for statistical significance. My results showed that elevated CO2 had a stimulating effect on most growth parameters, particularly when plants were given more time to grow. In a 100-day growth experiment, CO2 affected the number and dry biomass of plants of all species, regardless of their C3 or C¬4 photosynthetic pathways. Salinity consistently inhibited germination and growth at all stages, from germination through plant emergences, numbers of established plants, and dry biomasses at harvest. Interactive effects of CO2 and salinity did occur, though often in seemingly specific instances rather than forming clear and consistent trends. My findings suggested that growth of common grasses would be enhanced by the rising level of CO2 in the atmosphere, but the effect would be modified by environmental stresses, such as salinity.

The cell is the basic unit of all living organisms. It is an amazing machine capable of self-replicating, growing, and synthesizing and shuttling thousands of compounds. To perform all of these activities the cell needs energy. The original source of energy for all living beings is the Sun. The energy of the sun is collected by the autotrophs (mostly plants) through photosynthesis and stored in the chemical bonds of carbohydrates and lipids through carboxylic acid intermediates; animals use these compounds to obtain the energy for their cells. Most of the energy extracted by the cell comes from the citric acid cycle. Therefore, two crucial energy transfer checkpoints are photosynthesis and citric acid cycle. With growing need for energy, the limited supply of fossil fuel, and the search for a cleaner environment, scientists have turned to the Sun (directly or indirectly through wind, tides, biomass, etc.) to satisfy the needs of modern society trying to reach the dual Holy Grail of energy: harvesting energy through Artificial Photosynthesis and Low Temperature Biomass Oxidation. This work represents one more step toward reaching these Holy Grails. The core reagent used in our technique is ferritin. Ferritin recapitulates some of the essential features of a plant cell: it contains a semiconductor capable of charge separation, like chlorophyll, acts as a membrane to isolate compartments, and has an enzymatic activity that prevents charge build up and oxidative damage. The energy absorbed by ferritin from the artificial “solar” radiation is used to extract reducing equivalents from stable and partially oxidized compounds, mainly carboxylic acids. The energized electrons produced are then used for a number of technical applications, from synthesis of catalytically active nanoparticles, to reductive precipitation of contaminant heavy metals (i.e.: mercury), to hydrogen evolution.

Doctor of Philosophy / Department of Horticulture, Forestry, and Recreation Resources / Dale J. Bremer / Turfgrass covers 1.9% of the nation’s surface area and is the largest irrigated crop in the USA. Developed urbanized land is projected to double by 2025, which will increase turf’s environmental impact. Studies were conducted to evaluate environmental impacts by characterizing nitrogen, carbon, and water fluxes in turfgrass ecosystems. Emissions of nitrous oxide (N[subscript]2O), a major greenhouse gas and ozone depleter were measured from bermudagrass (Cynodon dactylon L. Pers. x C. transvaalensis Burtt-Davy) (bermuda), perennial ryegrass, (Lolium perenne L.) (rye), and zoysiagrass, (Zoysia japonica Steud.) (zoysia) under regional N management. In a separate study, N2O fluxes were measured from bermuda fertilized with controlled-release N fertilizers including polymer-coated and organic-N, and quick release urea. Emissions of N2O were measured using static surface chambers and gas chromatography. Zoysia, with less N requirements, had lower emissions than bermuda. Cumulative N[subscript]2O emissions were similar among N types. To measure water and carbon fluxes, a portable non-steady state chamber was designed and tested. The chamber had minimal affects to the canopy during field measurements: leak values averaged <1.5 micromol CO[subscript]2 m[superscript]-2 s[superscript]-1; average chamber pressure was 0.09 Pa ±0.01 Pa; temperature rise inside the chamber averaged 0.74C; and the chamber had 90% photosynthetically active radiation transmittance. Using the chamber, differences were detected in net photosynthesis (Pnet), gross photosynthesis (Pg), evapotranspiration (ET), canopy stomatal conductance (gc), and water use efficiency (WUE) in well-watered tall fescue (Festuca arundinacea Schreb.), Kentucky bluegrass (Poa pratensis L.) (KBG), zoysia, and bermuda. Irrigation requirements, visual quality ratings, and genetic rooting potential of 28 KBG cultivars and 2 Texas bluegrass hybrids (P. pratensis x P. arachnifera Torr.) were quantified in greenhouse and rainout facility studies. Average water applied ranged from 23.4 to 40.0 cm among cultivars. Bedazzled, Preakness, and Bartitia required less water and had higher average quality than other cultivars. Compact America and Mid-Atlantic phenotypes exhibited greatest potential for success in integrating reduced water inputs with maintenance of acceptable visual quality. Results indicated that turfgrass management could mitigate N[subscript]2O emissions and conserve water while maintaining healthy turfgrass, and the new chamber will enhance turfgrass studies by providing rapid measurements of photosynthesis.

Thesis (MSc (Biochemistry))--Stellenbosch University, 2008. / The aim of this study is the theoretical investigation of carbon fixation in sugarcane leaves. Sugarcane has a well known reputation for accumulating sucrose in the stalk to levels as high as 650 mM, almost a fifth of the plant’s fresh weight. Although this is an efficient accumulating mechanism, there is an even more efficient ‘carbon pump’ found in C4 plants. This is a well documented carbon concentrating mechanism and one of the first to be studied. However scientists are still trying to understand the carboxylating mechanism and the regulation thereof. It has been speculated that this mechanism is at its saturation level and elevating carbon dioxide will have little or no effect on further carbon fixation. Futher, studies suggest that the sucrose accumulating sink is able to regulate photosynthesis. Therefore a regulatory mechanism should exist from the sink to carbon fixation in order for such regulation to occur. Thework in this thesis therefore lays the foundation for investigating regulation of photosynthesis. The field of systems biology is the study of cellular networks by assemblingmodels. Pathways are considered as systems and notmerely collections of single components. This allows the interaction of pathway metabolites and the regulation that they have on one another to be studied. The questions asked pertaining to a pathway, will determine the types of model analysis. Structural analysis is useful for studying stoichiometric models, determining characteristics like energy consumption, futile cycles and valid pathways through a system at steady-state. Kinetic analysis on the other hand, gives insight into system dynamics and the control exerted by the system components, predicting time-course and steady states. In this thesis we begin to investigate photosynthesis in sugarcane leaves and the role it has in accumulating sucrose in the plant. Firstly, a structural model was developed incorporating carbon fixation, sucrose production in the leaf and subsequent transport of sucrose to the storage parenchyma and accumulation. The model was analysed using elementary mode analysis, showing that there are twelve routes for producing sucrose with no pathway beingmore energy efficient than any other. Further, it highlighted a futile cycle transporting triose phosphates and phosphoglycerate between the two photosynthetic compartments in the leaf. In the storage parenchyma, manymore futile cycleswere revealed,many of them energetically wasteful. Three other sets of elementary modes describe sucrose’s destination in either the vacuole or use in glycolysis or fibre formation, each with a different amount of required energy equivalents. The fourth set describes how sucrose cannot be converted to fibre precursors without also being used for glycolyis building blocks. Secondly, a kinetic model of carbon fixation in the leaf was assembled with the primary goal of characterising thismoiety-conserved cycle. This included the collation of kinetic data, incorporating volumes of the compartments and the areas of the location of the transporters into the model. This model was then analysed using metabolic control analysis. The model was able to predict metabolite concentration in the pathway at steady-state which were compared to those found experimentally. However, modifications need to be made to the model before further analysis is done so that the model predicted values match the experimental values more accurately. Time course analysis and response coefficients were also calculated for the carbon fixation cycle. Thework in this thesis therefore paves the way for understanding photosynthesis and its regulation in sugarcane leaves. Such work has the potential to pinpoint genetic engineering target points, allowing for better hybrid selection and propagation.