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CitationRoundy, B. A., Taylorson, R. B., & Sumrall, L. B. (1992). Germination responses of Lehmann lovegrass to light. Journal of Range Management, 45(1), 81-84.
PublisherSociety for Range Management
JournalJournal of Range Management
AbstractLebmann lovegrass (Eragrostis lehmanniana Nees.) is a perennial, warm-season bunchgrass that is native to South Africa and has been seeded and spread naturally in the southwestern United States. Germination of 4 seed lots of varying age was tested in relation to darkness and irradiance with red (R) and far-red (FR) light. Germination was low in continual darkness, but greatly increased after exposure to R. Irradiation with FR after exposure to R reduced germination, confirming phytochrome involvement. Exposure to R after prolonged imbibition in FR did not increase germination of 1-2-year-old seeds and only slightly increased germination of older seeds. An alternating temperature of 16 hours at 15 degrees C and 8 hours at 38 degrees C greatly increased germination of seeds exposed to fluorescent light and slightly increased germination of seeds in darkness compared to a constant temperature of 25 degrees C. Greater seedling emergence of Lehmann lovegrass when the canopy is opened by burning, mowing, or grazing is likely a function of red light stimulation of biologically active phytochrome and increased seedbed temperature fluctuations.
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Characterization of organic/organic' and organic/inorganic heterojunctions and their light-absorbing and light-emitting propertiesArmstrong, Neal R.; Anderson, Michele Lynn, 1968- (The University of Arizona., 1997)Increasing the efficiency and durability of organic light-emitting diodes (OLEDs) has attracted attention recently due to their prospective wide-spread use as flat-panel displays. The performance and efficiency of OLEDs is understood to be critically dependent on the quality of the device heterojunctions, and on matching the ionization potentials (IP) and the electron affinities (EA) of the luminescent material (LM) with those of the hole (HTA) and electron (ETA) transport agents, respectively. The color and bandwidth of OLED emission color is thought to reflect the packing of the molecules in the luminescent layer. Finally, materials stability under OLED operating conditions is a significant concern. LM, HTA, and ETA thin films were grown in ultra-high vacuum using the molecular beam epitaxy technique. Thin film structure was determined in situ using reflection high energy electron diffraction (RHEED) and ex situ using UV-Vis spectroscopy. LM, HTA, and ETA occupied frontier orbitals (IP) were characterized by ultraviolet photoelectron spectroscopy (UPS), and their unoccupied frontier orbitals (EA) estimated from UV-Vis and fluorescence spectroscopies in combination with the UPS results. The stability of the molecules toward vacuum deposition was verified by compositional analysis of thin film X-ray photoelectron spectra. The stability of these materials toward redox processes was evaluated by cyclic voltammetry in nonaqueous media. Electrochemical data provide a more accurate estimation of the EA since the energetics for addition of an electron to a neutral molecule can be probed directly. The energetic barriers to charge injection into each layer of the device has been correlated to OLED turn-on voltage, indicating that these measurements may be used to screen potential combinations of materials for OLEDs. The chemical reversibility of LM voltammetry appears to limit the performance and lifetimes of solid-state OLEDs due to degradation of the organic layers. The role of oxygen as an electron trap in OLEDs has also been verified electrochemically. Finally, a more accurate determination of the offset of the occupied energy levels at the interface between two organic layers has been achieved via in situ monitoring of the UPS spectrum during heterojunction formation.
Optimizing Carbon Dioxide Concentration and Daily Light Integral Combination in a Multi-Level Electrically Lighted Lettuce Production SystemKacira, Murat; Caplan, Brian Akira; Giacomelli, Gene; Cuello, Joel (The University of Arizona., 2018)There are many issues that will make producing sufficient food for the growing global population a difficult task. Controlled Environment Agriculture (CEA), integrating environmental control and hydroponic technology, can efficiently produce more food with less inputs. The new production practices of vertical farms have precision environmental control and subsequently more consistent and higher productivity with the advantage of being located almost anywhere, especially closer to population centers. A vertical Farm can be described as a fully indoor production system that uses electrical lamps for photosynthetic lighting and high density crops grown in multiple layers. CEA technology of supplementing atmospheric carbon dioxide (CO2) in greenhouse applications to compensate for low light levels, maintain plant photosynthesis, and enhance profits is practiced. However, due to the amount of ventilation generally required in greenhouse environments, maintaining CO2 concentrations can be expensive and impractical. The closed configuration of vertical farms can enhance CO2 use efficiency, however, the use of electrical lighting results in a large electrical power requirement. The goal of this study was to evaluate the level of daily light integrals (DLI) and atmospheric CO2 concentrations that would provide savings of electrical power usage and CO2 supplementation while producing a marketable head lettuce (Butterhead, cv. Fairly) product. Experiments were conducted in a 45 m2 environmentally controlled (air temperature, PPF, DLI, CO2, DO, EC and pH) vertical farm research facility with six values of DLI (9, 11, 13, 15, 17, 19 mol m-2 d-1) and six CO2 concentrations (400, 550, 700, 850, 1000, 1300 ppm), which were maintained constant from transplant through harvest. Plant shoot fresh and dry weights were measured at harvest and compared with resource use accounting of electrical energy for LED lighting, heat pumps for air conditioning, water pumps for nutrient solution circulation, and air pump to maintain dissolved oxygen in the nutrient solution for the roots. It was demonstrated that 1) a linear relationship of increase biomass to increase of DLI existed for all treatments; 2) plants within the 850 ppm CO2 concentration yielded the largest average fresh and dry shoot weights and yields decreased as CO2 was further elevated; 3) the physiological disorder tip burn was more pervasive and appeared sooner for either larger CO2 concentrations and larger DLIs. No tip burn was observed at 400 and 550 ppm CO2 concentrations within any DLI; 4) lettuce grown in lower light intensities had larger physical size dimensions, but were less dense and had less biomass, compared to lettuce grown in higher light intensities which had a smaller physical dimension, but were more dense and thus greater biomass; 5) the metrics for the average overall resource use efficiencies of plant production for fresh weight edible biomass were 69 gfresh kWh-1, 147 gfresh LCO2-1, 20.7 LH2O kgfresh-1 y-1 , and 86.0 kgfresh m-2 y-1; 6) the potential electrical savings from changing the DLI (mol m-2 d-1)/CO2 (ppm) combination from 17/400 to 13/850 in the small scale research facility, to which this study was conducted, is $59 per harvest and $762 for the year (14.4% savings). Larger commercial vertical farm operations lowering the DLI and increasing CO2 concentrations could have a much greater electrical savings potential.