Plant Science & Landscape Architecture Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2797
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Item ENHANCING QUALITY OF LIFE ON URBAN RESIDENTIAL STREETS BY CREATING PLACES FOR PEOPLE AND TREES(2019) PARKER, PAMELA; Ellis, Christopher; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lower income urban rowhouse neighborhoods are often treeless with only narrow sidewalks separating the front door from the street. This thesis explores the opportunity to capitalize on the predicted shift from private automobile ownership to fleets of autonomous vehicles and the subsequent significant drop in parking demand. Space previously designated as parking lanes can be converted into continuous tree planting strips and social spaces along inner-city residential streets. In this thesis, I propose three streetscape models utilizing the space no longer needed for parking: 1) the James Street Private Model that designs a 10’ wide continuous tree planting strip, allowing trees, gardens and patios to be installed along the foot of the rowhouse steps; 2) the James Street Public Model that creates the same tree strip design but positions it between the sidewalk and the street; and 3) the Shared Street Model, set along a narrower alley street, that forms a meandering road shared with pedestrians, public spaces and trees. These streetscape improvements directly address the quality of life of the residents by enhancing their safety and security, physical surroundings, social relations and health.Item FUSARIUM SPECIES OF CUCUMIS MELO IN THE MID-ATLANTIC REGION OF THE US AND THEIR IMPACT ON SALMONELLA ENTERICA NEWPORT SURVIVAL AND INTERNALIZATION ON VARIOUS MELON CULTIVARS.(2019) Korir, Robert Cheruiyot; Everts, Dr. Kathryne L; Micallef, Dr. Shirley A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fruit rots caused by Fusarium spp. can lead to economic yield losses on melon (Cucumis melo). However, which Fusarium spp. are the most prevalent in Maryland and Delaware has not been documented. Several Salmonella enterica subsp. serovar Newport (S. Newport) outbreaks on melon have occurred over the past 25 years. Fusarium spp. infestation on melon have potential impact on survival and colonization of Salmonella. Our objectives were to identify Fusarium spp. infestations on melons within the Delmarva region, and evaluate their impact on survival and internalization of S. Newport on various melon cultivars. Fifty-six isolates were molecularly identified, according to Fusarium-ID online database, as Fusarium spp. (Fusarium fujikuroi-20, Fusarium proliferatum-18, Fusarium oxysporum-15, Fusarium graminearium-2, Fusarium verticilloides-1). Our findings revealed that most of the Fusarium isolates we collected were not pathogenic to melon fruit. We evaluated the impact of four Fusarium spp. (F. armeniacum, F. oxysporum, F. fujikuroi, and F. proliferatum) on S. Newport survival in five melon cultivars; ‘Arava’ (C. melo var. reticulatus, Galia), ‘Athena’ (var. reticulatus, muskmelon), ‘Dulce Nectar’ (var. inodorus, honeydew), ‘Jaune de Canaries’ (var. inodorus, Canary), and ‘Sivan’ (var. cantalupensis, Charentais). Impact of F. proliferatum on survival and interlization of S. Newport was evaluated on honeydew (smooth) and cantaloupe (netted) melons. Generally, Fusarium did not impact the survival of S. Newport, however greater survival of S. Newport was observed on the netted cultivars compared to the smooth surface melons. Fusarium fujikuroi significantly enhanced survival of Salmonella when inoculated on riper ‘Jaune de Canaries’ melons (above ¾ slip). However, when the experiments were replicated with less ripe (about ¾ slip) melon, F. fujikuroi did not significantly influence the growth of S. Newport. Salmonella Newport internalized in all treatments and the cantaloupe and honeydew melons, but variation in population levels were observed across the treatments. Overall, Fusarium proliferatum did not impact internalization of S. Newport on either melon type. This may be attributed to that Fusarium species used during this study were non-pathogenic. Salmonella Newport recovered gradually decreased with time. Fusarium species on melon, influence S. Newport colonization differently. Also, melon rind type affects the ability of S. Newport to survive and colonize differently.Item SPATIO-TEMPORAL ANALYSIS OF PHOTOTROPISM IN ARABIDOPSIS SEEDLINGS(2019) Pritchard, Candace; Murphy, Angus S; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Optimization of light capture during seedling development is a major determinant of plant fitness. As seedlings emerge from the soil, the processes of photomorphogenesis and phototropism optimize deployment of structures that capture light for photosynthesis. Photomorphogenesis produces hypocotyl thickening, cotyledon expansion, and chloroplast maturation. Concurrent phototropic responses initiated by blue light position the expanding cotyledons to maximize photosynthesis. The mechanisms underlying both processes have been explored for more than 140 years, but are still not fully understood. This dissertation seeks to provide a better understanding of phototropism by exploring the timing and localization of the constituent mechanisms downstream of the well-characterized perception of blue light by the PHOTOTROPIN photoreceptors. The experiments described herein characterize temporally and spatially distinct processes involved in asymmetric auxin accumulations that lead to differential hypocotyl elongation. To better identify the link between early perception and later auxin transport and elongation events, an open-air system was used to remove seedling hindrance and provide better spatio-temporal resolution. These experiments confirmed the more rapid bending conferred by loss of the ATP Binding Cassette class B (ABCB) 19 auxin efflux transporter and loss of differential elongation in the mid hypocotyl elongation zone in higher order pinformed mutants. However, apart from the enhancement of phototropic bending observed in abcb19 and pin4 mutants, no auxin transport mutants tested showed alterations in early phototropic responses, and no mutant exhibited a delay in the onset of phototropic bending. Recently identified CBC1 and CBC2 (CONVERGENCE OF BLUE LIGHT (BL) AND CO2 1/2) have been shown to act in downstream signaling during phot1-mediated regulation of stomatal conductance. Similarly, during phototropism cbc1cbc2 double mutants show early defects in phot1-mediated phototropism. Further, CBC1 and CBC2 have been shown to regulate S-type anion channels. Analysis of S-type anion channel mutants also reveals defects in early bending responses. These results point to blue light-dependent regulation of anion channel activity having an important role during the earliest stages of phototropism.Item Nitrogen cycling by grass-brassica mixtures in the Mid-Atlantic(2019) Gaimaro, Joshua Ruben; Tully, Kate; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mixtures of cover crop species may be more effective than monocultures at internal nutrient cycling due to their ability to occupy different niches. Our study investigates nitrogen (N) cycling of radish (Raphanus sativus L.) and rye (Secale cereal L.) in monocultures and mixtures compared to a no cover crop control. The study was established on fine-textured soils near Laurel, MD where we estimated N leaching losses, quantified mineral soil N (to 60 cm), and cover crop biomass N for two years. Forage radish suppressed estimated N leaching in the fall, while cereal rye suppressed estimated N leaching in the spring. In this study, growing radish in a mixture with rye decreased the risk of N leaching losses and enhanced N cycling due to the difference in timing of N uptake and release. Our research indicates that grass-brassica mixtures are a flexible management tool for mitigating N leaching in the Mid-Atlantic.Item SALMONELLA ENTERICA STRATEGIES FOR PERSISTENCE ON TOMATO (SOLANUM LYCOPERSICUM) AND SEROVAR DYNAMICS IN SURFACE AND RECLAIMED WATER(2019) Ferelli, Angela Marie Cecelia; Micallef, Shirley A.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)While select aspects of Salmonella enterica subspecies enterica persistence in agricultural matrices have been illustrated, serovar specific survival strategies in surface water, transmission, and persistence on plants are multifaceted and remain only partially examined. In the present work, we utilized an interdisciplinary approach to illustrate novel mechanisms by which S. enterica may adapt to plants as an alternative host. Furthermore, we leveraged the wealth of diversity in S. enterica serovars to investigate specific dynamics and drivers of persistence in water and transfer onto produce crops. Through biochemical, gene expression, and plant challenge assays of both tomato (Solanum lycopersicum) vegetative and fruit organs, we found that plant-derived NO was generated in response to S. Newport recognition. Furthermore, bacterial gene expression on both leaves and fruit was indicative of adaptation to a novel environment including upregulation in NO detoxification machinery, indicating plant-derived NO as a novel bacterial stress. NO tolerance of various S. enterica was then evaluated to investigate drivers of “produce associated’ S. enterica adaptation to the plant niche. We identified that plant derived NO can negatively affect titers of all S. enterica serovars tested and that serovar specific tolerance to NO in vitro was apparent in a concentration and exposure time dependent manner. Finally, the survival of various S. enterica in surface and reclaimed water was investigated while evaluating the potential for transition to viable but non-culturable (VBNC) organisms. Furthermore, surface water used for irrigation, a common water environment for S. enterica, was investigated as a priming reservoir for various S. enterica serovars for enhanced transmission onto tomato crops. Persistence in water included VBNC subpopulations and was driven by water type. Transfer success onto tomato was driven by serovar, and prolonged incubation in water increased the transfer ability of serovars that initially transferred poorly onto tomato. Finally, attachment to polystyrene and water oxidation-reduction potential were identified as possible indicators of foodborne pathogen transfer success onto tomato. Moving forward, a greater understanding of the environmental queues used by S. enterica subspecies enterica responding to the agricultural environment will aid researchers in developing S. enterica targeted on-farm management techniques to ensure safe yet sustainable fresh produce cultivation practices.Item ECO-HABITATS - USING ECOLOGICAL DESIGN FOR AMPHIBIAN AND REPTILE HABITATS ON GOLF COURSES: CASE STUDY AT LANGSTON GOLF COURSE, WASHINGTON, D.C.(2019) Simpson, Lotoia; Myers, David N; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Habitat restoration is useful to address the loss of amphibian and reptile habitats in the built environment. Golf courses provide the opportunity to implement best management practices and best development practices features to improve habitats for amphibians and reptiles. In addition, golf courses, through creative programming offer opportunities to provide education about amphibians and reptiles. This research project focuses on the application of vernal pools and regenerative stream conveyance (RSC) interventions for Langston Golf Course, a historically designated golf course in Washington, D.C. In addition, the implementation of additional programming allows for educational opportunities about amphibians and reptiles for expanded variety of users beyond golfers.Item EXPERIENTIAL LANDSCAPE DESIGN FOR EDUCATION: OXON RUN PARK AS A REGIONAL EDUCATION RESOURCE(2019) Ferguson, Katherine; Chanse, Victoria; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This design-research thesis explores the educational benefits of outdoor experiential learning for children, particularly in urban areas, and proposes a redesign of a 100-acre urban park to serve as an educational resource. This thesis first develops a theoretical framework based on research that nature can have restorative effects on attention that improve learning and behavior (Berman, Jonides, & Kaplan, 2008; Kaplan, 1995; Matsuoka, 2010). The focus of this thesis is Oxon Run Park located in Southeast Washington, DC. The proposed redesign includes educational spaces that can be visited and experienced by the local community or school classes, while focus areas at targeted locations concentrate educational resources that can enhance classroom learning. The research and redesign of Oxon Run Park addresses the question of how public spaces can be designed to serve as educational resources.Item Westport Waterfront: An Alternative Approach to Post-Industrial Rejuvenation in Baltimore(2019) Zhang, Keren; Sullivan, Jack; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Abandoned post-industrial sites are often seen as a representation of pollution and desolation. The neighborhoods near these sites, which no longer employ the local citizenry, often struggle with crime, unemployment and decaying residential and commercial properties. Nevertheless, post-industrial sites can contain some of the most interesting histories of the city and should be viewed as an opportunity for the local community to redevelop with meaning and purpose in a sustainable way. Like many post-industrial area, the Westport neighborhood in Baltimore struggles with crime, unemployment, housing abandonment and a lack of commercial properties, and is redesigned in thesis to explore how post-industrial site redevelopment can reconnect residents with waterfront and revive communities. This thesis will explore the options for establishing an equitable, viable and productive community that contributes to the well-being of the existing population through the reuse of the post-industrial waterfront property.Item IDENTIFYING HIGHLY CONSERVED PATHOGENICITY GENES IN CHESTNUT BLIGHT AND POWDERY MILDEW FUNGI AS TARGETS FOR NOVEL FORMS OF HOST RESISTANCE(2019) Levine, Bruce Jonathan; Xiao, Shunyuan; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A bioinformatic search of the genomes of chestnut blight fungus, Cryphonectria parasitica (Cp), and the Arabidopsis powdery mildew fungus, Golovinomyces cichoracearum (Gc), yielded six suspected pathogenicity genes with homologues in both species. Deletion of these genes by homologous gene replacement was attempted in Cp, with one success, TG4. The TG4-knockout strain showed changes in phenotype and reduced fungal virulence against chestnut. TG4 appears to be a promising target for host-induced gene silencing (HIGS) in transgenic American chestnut. The use of homologues from genetically tractable species like Cp can help overcome the obstacles to performing reverse genetics on intractable, biotrophic fungi such as Gc. Experiments underway involving the silencing and ectopic overexpression of the Gc homologues of the target genes provide a rapid method to study Cp genes, including to screen additional candidate genes as future targets for HIGS.Item ECOPHYSIOLOGICAL AND SOCIAL FUNCTIONS OF URBAN FOREST PATCHES(2019) Sonti, Nancy Falxa; Sullivan, Joseph H; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Urban trees provide many ecosystem services to cities: alleviating the urban heat island effect, absorbing stormwater runoff, and contributing to residents’ social and psychological well-being. The production of these benefits is influenced by tree growth and physiological function within the urban ecosystem, and also by the social-ecological context in which urban forest patches exist. This dissertation investigates the ecophysiological and social functions of urban forest patches of the eastern United States using a multidisciplinary approach that combines diverse empirical methods across varied timescales and geographies. Using data collected from urban and reference forest patch sites, this dissertation begins by addressing the following questions: How does native tree growth and physiology vary between urban and reference forest patches? Are there differences in ecophysiological responses by tree species and by city within the eastern United States? Air temperature and soil data from each field site are analyzed alongside tree ring and leaf-level physiological data. Next, results from a controlled growth chamber experiment are presented to examine how Baltimore’s urban vs. reference forest soils and air temperature interact to affect seed germination and seedling growth of white oak (Quercus alba), a dominant species in the region. Finally, the social functions of forest patches are investigated using qualitative data from semi-structured interviews conducted with Baltimore residents. Overall, urban forest patches were found to support robust growth and physiological function of white oak (Quercus alba L.) and red maple (Acer rubrum L.) trees, with differences by species and site type (urban vs. reference), and over time. In particular, urban soils appear to support greater biomass and photosynthesis rates than reference soils. Regardless of the favorable ecophysiological conditions of urban forest patches, community awareness and engagement with these sites will be critical to their continued protection and management. Qualitative interview data revealed local residents’ strongly ambivalent attitudes towards urban wilderness, with only limited differences by homeownership and property management regime. In sum, dissertation documents important ecophysiological and social functions of urban forest patches, with implications for the continued provision of benefits to urban and rural communities.