Plant Science & Landscape Architecture Theses and Dissertations

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    Dual water quality responses after more than 30 years of agricultural management practices in the rural headwaters of the Choptank River basin in the Chesapeake Bay watershed
    (2023) Silaphone, Keota; Fisher, Thomas R; Natural Resource Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Eutrophication is the water quality response to over-enrichment by nitrogen (N) and phosphorus (P) in fresh, estuarine, and coastal waters globally. Agricultural best management practices (BMPs) are the primary tool for controlling eutrophication in rural areas, particularly in the Chesapeake Bay watershed, where BMPs are vital to achieving TMDL goals. However, despite the application of BMPs, local water quality in the headwaters of the Choptank River, a major tributary of the Chesapeake Bay on the Delmarva Peninsula, has not improved. Thus, further investigation of agricultural BMP impacts on water quality in the Greensboro watershed is needed. My overarching research question is, “Why have N and P concentrations increased at the USGS Greensboro gauge if agricultural Best Management Practices (BMPs) have been implemented?” I applied statistical approaches to three linked, testable hypotheses to systematically evaluate agricultural BMPs and their impacts on nutrient (N and P) export from the Greensboro watershed. My first hypothesis was that agricultural BMPs have increased significantly in the Greensboro watershed. To test this hypothesis, I obtained publicly available modeling data via the Chesapeake Assessment Scenario Tool (CAST) and estimated the subsequent edge-of-stream N and P export. My findings indicated that the number of BMPs in the agricultural sector increased significantly between 1985 and 2021, supporting the hypothesis. Overall, modeled agricultural N and P export significantly decreased between 2010 and 2021 (p < 0.001). However, the modeled edge-of-stream agricultural nutrient export resulted in no significant change in N export and an increase of 3% in agricultural P export resulting from BMP implementation levels in 2021 compared to 2010. This study demonstrated the use of CAST to acquire reported BMP implementation levels and increased nutrient inputs into the Greensboro watershed between 1985 and 2021. The watershed nutrient inputs mirror the upward trends in N and P export captured by the USGS long-term monitoring station at Greensboro. With this improved access to BMP implementation and nutrient data, decision-makers can consider adaptive management measures to decrease nutrient export downstream. My second hypothesis was that agricultural BMPs have an adequate basis for estimating their capacity to reduce N export. To test this hypothesis, I conducted a meta-analysis on 689 cover crop N efficiencies reported in 18 empirical and modeling studies. The cover crop N efficiency was calculated as the ratio of an N interception by cover crop biomass or a reduction in soil or groundwater N divided by an N input, e.g., previous spring fertilizer or a previous soil or groundwater N concentration or flux. These variable approaches resulted in wide ranges in mean cover crop N efficiency (10-80%) due to empirical and modeling experimental approaches, varying methods, and parameters used to calculate efficiency. The modeling approach generally resulted in N efficiency values significantly higher than the empirical approach, as did the parallel control-treatment experiments compared to the sequential before-and-after implementation method. Because of these variables, there appears to be no standard methodology to report the effects of cover crops or standardized metadata describing the variables used in the N efficiency calculations. I suggest a standard methodology and metadata that should accompany future reports of cover crop N efficiencies to improve the modeled effects of BMPs on nutrient export. My third hypothesis was that three methods of estimating N and P concentrations and yields are in agreement and show a relationship to BMP implementation in the Greensboro watershed. To test this hypothesis, I compiled annual nutrient (N and P) datasets based on (1) USGS field measurements of concentrations and discharge, (2) USGS flow-normalized weighted regression based on time, discharge, and season (WRTDS) of concentrations and yields, and (3) CAST-modeled nutrient yields. Statistical analyses revealed time, discharge, agricultural BMPs, and animal waste management practice trends of the three methods. Results indicated that the USGS field measurements and WRTDS flow-normalization methods consistently showed an increase in N and P concentrations and yields. In contrast, all CAST-modeled regressions showed significantly decreasing nutrient concentrations and yields (p ≤ 0.05), which did not support the hypothesis that all three methods are in agreement. Despite CAST-modeled results decreasing with increasing BMPs, which supports the hypothesis that N and P concentrations and yields show a relationship with BMP implementation, USGS methods resulted in increasing nutrient concentrations and trends. These results indicated significant underestimates of modeled N and P export by CAST. I recommend using adjusted BMP efficiencies during cultural and structural BMP lifespans to improve model outputs. I also suggest two approaches to reflect the role of annual poultry manure applications: (1) model nutrient transport via artificial drainage ditches that interfere with natural nutrient flow pathways and exacerbate N and P transport, and (2) model the accumulation of soil-P and saturated soil-P, resulting in increases in dissolved P and particulate P in downstream surface waters. Agronomic recommendations include developing efficient manure recycling approaches within the local agricultural systems via nutrient management practices and concurrent research and development to support alternative uses of animal waste, including composting, bioenergy generation, granulating/pelletizing, and establishing a marketplace to support the sale of these products and to offset the costs of transporting manure from areas of manure surplus to manure deficit areas. This dissertation revealed that modeling studies overestimate cover crop N efficiencies in the United States Coastal Plain province and that CAST modeling is not in agreement with the USGS field measurements. CAST-modeled nutrient concentrations and yields decrease over time, indicating improvements in water quality. In contrast, USGS methods consistently show that nutrient concentrations and yields increase, indicating that BMPs are insufficient, inadequate, overwhelmed by nutrient inputs, or efficiencies are overestimated. Indeed, nutrient-reducing BMPs have increased between 1985 and 2021. With over 35 years of BMP implementation, measurable water quality response is expected. However, BMPs that relocate and apply higher amounts of manure annually have also increased with nutrient-reducing BMPs. Rising manure application rates combined with higher fertilizer application rates due to economic pressures on farmers to increase crop yields appeared to have overwhelmed implemented BMPs. Continued manure applications onto croplands in the Greensboro watershed suggest nutrient export will continue to rise; thus, reaching water quality goals is unlikely.
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    A Place in Public Space: Designing an Autism-Friendly Experience for Adults in Palmer Park
    (2023) Ada, Micaela; Sachs, Naomi A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In 2023, the CDC reported that approximately 1 in 36 children in the U.S. is diagnosed with autism spectrum disorder (ASD). Prevalence rates have nearly doubled every decade since the CDC began tracking this data in 2000. When these children come of age and enter adulthood, they face new milestones and challenges such as working, living away from the family home, and navigating the world with more autonomy. Design professions —including architecture, interior design, and landscape architecture— have progressively incorporated considerations for ASD into their spaces. Adult-specific, autism-friendly design guidelines existing today have honed in on improving workplace, home, and therapeutic environments. There is a noticeable gap in addressing landscapes made for the social and leisure aspects of life. To address this gap, this research design thesis focuses on implementing design interventions in Landover, MD’s Palmer Park Community Center outdoors space to create an autism-friendly space for adults seeking comfortable recreation opportunities.
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    Understanding organic and conventional management programs and rhizosphere microbiome for sports turf in Maryland
    (2023) Peddigari, Shravya; Carroll, Mark; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In response to public concerns about exposure to pesticides, some state and local municipalities have placed restrictions on the use of pesticides on athletic fields. When such restrictions are implemented athletic field management often transitions to the use of natural or organic turf care with little understanding of how the transition away from conventional management practices may affect surface conditions and soil microbial properties.This thesis examined the use of organic and conventional management programs on the turf quality, surface hardness, and shear strength of engineered soil cap, hybrid bermudagrass (Cynodon dactylon x Cynodon transvaalensis) athletic fields, as well as the impact of the two programs on the rhizosphere microbiome. Turf quality was assessed by visual means and by obtaining normalized difference vegetative index (NDVI) readings of the turf canopy. Surface hardness was determined using a Clegg impact surface tester. The rotational shear strength of the surface was measured using a shear vane. The study was conducted for 3 years at two different locations; research plots at the University of Maryland Research Facility and on athletic fields at Laytonia Recreational Park, in Gaithersburg, MD. Surface property data was collected monthly. Turf visual quality and NDVI data revealed use of the organic management program led to higher visual quality during spring, which was primarily the result of the spring retention of fall overseeded intermediate ryegrass (Lolium x hybridum Hausskn) and early season use of natural based fertilizers. In the summer months, crabgrass (Digitaria ischaemum Schreb.) encroachment was limited to the organically managed turfgrass. At both locations, clover (Trifolium repens) encroachment developed by the third year of the study, but the presence of this weed had limited impact on turfgrass quality. There were few significant differences in surface hardness and shear strength between the two management practices over the entire study period. The rhizosphere microbiome data, which was collected 12, 20, and 24 months after the initiation of two programs, did not show any significant difference between the organic and conventional management athletic fields in microbial abundance and/or diversity. The results of this study emphasize that the adoption of organic management programs on bermudagrass athletic fields should, in most instances, center on the establishment of acceptable weed tolerance levels for these fields. The use of organic management programs in the transition zone offers a viable alternative to the conventional chemical management of athletic fields, however over time, growing weed seed banks may necessitate the need for the occasional use of conventional herbicide materials.
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    (2023) Schulden, Taylor Francis; Rawat, Nidhi; Erwin, John; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The tertiary gene pool of wheat includes wild relatives like Aegilops geniculata (UUMM, 2n=4x=28) that are valuable genetic reservoirs for novel abiotic and biotic resistance genes. However, modern wheat varieties share limited genomic commonality with these gene pool members presenting barriers to recombination and genetic mapping of desirable genes. We mapped a broad-spectrum leaf rust resistance gene Lr57 located on chromosome 5Mg of Ae. geniculata using a simple but powerful methodology for high-resolution genetic mapping in tertiary gene pool members of wheat. Five gene candidates were revealed all with possible defense related functions. Strategic application of differential expression analysis, Virus-Induced Gene Silencing, and mutagenesis analysis reduced the candidate gene of interest to a singular and novel ID-NLR resistance gene containg a protein kinase, NB-Arc, and LRR domain. Using multiple strategies, validation of Lr57 candidate was completed. Gene complementation by transformation of Lr57 candidate is currently being conducted.
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    (2023) Shah, Jainee Priyesh; Ellis, Christopher D; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A very significant element of the city of Washington D.C. are its rivers. These rivers have been supporting the civilization around them for years. The Anacostia river has been subject to industrialization for centuries and it has been exposed to pollution mainly due to urban waste and storm water runoff. This pollution not only affects the water quality of the river but also impacts the nearby population, aquatic life and other species in many harmful ways. It is essential that development should take place considering the needs of people as well as the environment. Here, application of various green infrastructure techniques plays an important role in creating a balance. This thesis is an effort towards improving the water quality of the Anacostia River, reconnecting the city to its river and ensuring a healthy environment for humans and other dependent species.
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    The kinetics and quantum yield of photophosphorylation in Anacystis nidulans (Richt.) Drouet
    (1972) Owens, Olga v. H.; Krauss, Robert W.; Plant Physiology; Digital Repository at the University of Maryland; University of Maryland (College Park, MD)
    The active metabolite, ATP, serves not only as a high energy intermediate but also as a controller of some enzymatic reactions. In plant cells, the larger part of the ATP is formed by photophosphorylation. In this paper the rates, the quantum yields, and the wavelength dependencies of photophosphorylation in the blue-green alga Anacystis nidulans are reported. A fluorometric method for determination of enzymatically produced NADPH from ATP was adapted for use on cell extracts. In the light, the ATP level was 0.15 to 0.25 µmoles/mg chl. In the dark, the ATP level was 70% of that in light. In both darkness and anaerobosis, the level was 20%. A return to the light restored the ATP level from both conditions. Dark, anaerobic cells were exposed to measured irradiancies of 710 nm and 620 nm. The rate of ATP formation was measured within the first few seconds and found to be directly proportional to absorbed intensity. Saturation of the rates occurred at an intensity one-tenth the optimum for oxygen production. Quantum requirements of 6-8 were similar for each of the two wavelengths. The system II inhibitor DCMU, had a greater effect at 620 nm that at 710 nm indicating an involvement of system II in photophosphorylation only at 620 nm. At low intensities and over long time periods white light failed to produce a saturating steady-state level of ATP indicating a simultaneous consumption of ATP. Measurements in short dark periods following marginal illumination showed consumption of ATP to be 2 to 4 times greater that production in weak light. Thus, the quantum requirement can be calculated to be 2. ATP formation, therefore, is not the limit ing factor in co2 fixation. The evidence is the high quantum yield of photophosphorylation and the unsaturation of co2 fixation at intensities at which ATP synthesis is saturated.
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    (2023) Smith, Marci-Ann; Sachs, Naomi A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    With the rising trend of mental health issues among young adults, many colleges are trying to establish an approach to combat those issues for the well-being of their students. One such approach is Nature Rx. Nature Rx is a program that encourages people, sometimes with an actual prescription, to spend time in nature in order to relieve stress and improve overall health. Nature Rx is a holistic way of addressing mental issues such as stress, anxiety, and depression that are prevalent among college students. The evidence is strong that time spent in and engaging with nature can improve mental and physical health. Colleges like Cornell University and University of Maryland College Park are taking advantage of their existing beautiful landscape as part of their Nature Rx program to help their students. Other schools are implementing this program and providing spaces for their students to find reprieve from the stresses of studies. However, there is a gap in the presence of Nature Rx programs at Historically Black Colleges and Universities (HBCUs). To date, no HBCU has a nature Rx program. This project seeks to fill that gap by using the University of Maryland Eastern Shore, an HBCU, as a case study to answer the following thesis question: “How could a Nature Rx design at the University of Maryland Eastern Shore, a Historically Black College and University, benefit the health and well-being of its students?”
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    (2023) Shteinberg, Debra; Sullivan, Jack; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This thesis explores the ways in which lighting can be used to create a memorable nocturnal experience that engages users and strengthens connections to their landscapes. Far more than functional, lighting is an art form that can be used to transform the very way we understand and experience our public spaces. Through the lens of lighting design, a redesign of the FDR Beach and Boardwalk is proposed in response to the building of the East Shore Seawall, a large-scale infrastructure project that will threaten the community’s ability to engage with this vital open space. Lighting is used to create spaces that allow for entertainment, education, and reflection, which will activate the site, providing legibility, enhance the nighttime experience, and create a sense of identity.
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    (2023) Reise, Matthew; Sullivan, Jack; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The Crownsville State Hospital opened in 1913 as the first and only mental institution in the state of Maryland to serve the Black community. After 91 years of operation rife with neglect, abuse, exploitation, and other acts of inhumanity, the hospital closed and has laid virtually abandoned since. In this thesis, I will propose ways of reactivating Crownsville’s historic campus through acknowledging the property’s horrific past, by providing support and amenities to the region’s most vulnerable individuals, and by creating space to celebrate the identity of communities who were historically persecuted on the grounds. I will explore the Crownsville campus through the lens of a cultural landscape, and attempt to balance the preservation of existing assets with the development of new community features.
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    (2023) Callahan, Erin O'Dell; Sullivan, Jack; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Historic landscapes are an important part of our collective heritage. They provide a window to the past, offering narratives of our origins and how our relationships with nature have changed over time. Such landscapes receive historic treatments, including preservation, to ensure they are suspended in their period of significance. However, this static approach is no longer effective in protecting and communicating the heritage historic landscapes were intended to share: new approaches must be considered to contend with the dynamism of both nature and culture and ensure the health of these landscapes for generations to come. As climate change is the biggest threat to such landscapes, this thesis aims to explore how climate adaptive strategies can be responsive to both the historic and contemporary context of Meridian Hill Park: a cultural landscape that has been on the National Historic Register since 1994. It will focus specifically on providing meaningful experiences for children in the landscape, as a changing climate and environment is what they will inherit.
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    Applying Green Complete Streets on Georgia Avenue NW: Redesigning an Urban Right-of-Way for Sustainable Mobility and Urban Water Quality
    (2023) Mejias, Aliya; Ellis, Christopher D.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The public right-of-way (ROW) makes up nearly one-third of all the public space in cities. With the majority global population expected to reside in cities by 2050, climate change posing a significant threat to urban residents and infrastructure, impervious urban surface impacts on water quality, and knowing traffic fatalities in the US reached a 16-year high, cities must reconsider how this public good can serve people and the environment over to car-centric mobility. Using a segment of Georgia Avenue NW in Washington, DC, this thesis removes automobiles from the ROW to demonstrate how Green Complete Streets, which prioritizes sustainable transportation and urban water quality, can support urban livability on a corridor scale.
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    The Brain Does Not Lie: A Case Study of Psychophysiology and Landscape in South Clifton Park
    (2023) Seiz, Audrey; Kweon, Byoung-Suk; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Researchers have long explored how humans respond psychologically and physiologically to distinct landscapes and natural features. Walking in nature and viewing photographs of natural landscapes have been shown to reduce stress measured through physiological responses of blood pressure, salivary cortisol concentration, and pulse rate. Exposure to natural landscapes has also been shown to improve feelings of relaxation and positive emotion. The increased popularity of virtual reality (VR) in landscape architecture provides an additional visualization tool to immerse a participant in a landscape at human scale. Little research has focused on the potential impact of visualization through VR, studied the impact of urban nature, or compared the impact of landscape design using the same site. This study explores how employment of psychophysiological measures provides objective assessment of humans' landscape perception in response to the restorativeness of a virtual place. Twenty students were recruited to view an actual site in South Clifton Park, Baltimore City. Utilizing VR, participants observed the site as it exists currently and reimagined using the tenets of Attention Restoration Theory (ART), Stress Reduction Theory (SRT), and community vision. Psychological response was analyzed using the Perceived Restorativeness Scale (PRS-16), a survey designed to evaluate a place’s restorativeness through principles of ART, and physiological response was analyzed using electroencephalogram (EEG), the non-invasive measurements of the electrical brain activity. Findings indicated that perceived restorativeness increased in the designed site for the factors Being Away/Fascination and Compatibility; however, no significant difference was identified for the factor Extent. Regarding EEG data, alpha brain frequencies (broadband alpha, low alpha, and high alpha) were not significantly different when viewing the vacant versus designed site within the frontal or parietal lobes; however, beta brain frequencies (broadband beta, low beta, and high beta) demonstrated a marginally significant effect of sex in the frontal and parietal lobes with male beta brain frequencies decreasing when viewing the designed site and female beta brain frequencies increasing. Finally, frontal alpha asymmetry, a measure of approach-withdrawal motivation, demonstrated a marginally significant decrease when viewing the designed site, indicating increased withdrawal motivation in the designed site. The present research seeks to fill a gap in understanding objective indicators of restorativeness of a place and explore the power of VR as a tool for visualizing place.
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    Reimagining Vacant Assets with a Land Use Economy System: Design to deliver diverse benefits
    (2023) Marshall, Lauren EL; Sachs, Naomi A; Sullivan, Joe; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The City of Baltimore has more than 16,000 vacant structures awaiting demolition, and with more than 200 properties coming down each year, a surplus of vacant land it does not have the resources to maintain. These unmaintained vacant parcels erode already distressed neighborhoods, decreasing safety and serving as breeding grounds for unwanted pests. Current research shows that well designed and maintained projects on vacant properties can be community amenities, increasing adjacent property values, treating stormwater, lowering crime rates, reducing dangerous summer temperatures, and improving mental and physical health. There are vacant land restoration strategies in post-industrial cities across the United States that propose interventions ranging from installing raingardens to creating urban forests. What many of these strategies lack, however, is an intentional approach to designing a system for vacant land restoration that delivers key outcomes and creates conditions to attract the resources needed for implementation and maintenance. This lack often leaves cities struggling to find capital to address the glut of vacancies across the landscape. The specific objective of this project was to improve the lives of the people by strategically restoring vacant parcels through a systems-based approach. By employing a transdisciplinary research process rooted in community power sharing, this research uncovers key components to a vacant land restoration economy system in Baltimore. An assessment of groups interested in vacant land restoration offers a replicable methodology for uncovering desired outcomes from potential funders such as cleaner water, safer neighborhoods and jobs for underemployed people. The researchers then conducted a literature review to develop design strategies for delivering identified outcomes. These design guidelines were then applied to a vacant property in the Johnston Square neighborhood of Baltimore. A community engagement process co-designed with neighborhood leaders identified community desired outcomes and features for a vacant property then the research created designs in an iterative process with community members. Finally, the potential outcomes of that design were modeled using the National Green Values Calculator and the Community-enabled Lifecycle Analysis of Stormwater Infrastructure Costs, two models designed to look at social, economic, and environmental impacts of green infrastructure. This project advances the field of landscape architecture by offering a model by which planning and design can position vacant parcels to deliver critical benefits that create the conditions for public and private reinvestment. The project positions planning and design as tools to translate best available science in landscape processes into functional elements of places that support communities while delivering services and outcomes. This project has the potential to improve the quality of life for residents of Baltimore by delivering outcomes such as cleaner water, cooler temperatures, safer neighborhoods and jobs. It can also serve as a template for cities that are struggling with similar vacancy issues.
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    (2023) Perkins, Carrie; Neel, Maile C.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The macrophyte Vallisneria americana Michx. (Hydrocharitaceae) is a foundational submersed aquatic vegetation (SAV) species that provides valuable ecosystem services, such as nutrition for waterfowl and shelter for fish. When healthy, V. americana can absorb excess nutrients from the water and stabilize sediments, but many of its meadows, which span freshwater to oligohaline environments in eastern North America, have been declining since European settlers cleared the land. Declines only intensified in the 1950s due to chronic environmental stressors and major storm events. To determine the extent to which remaining populations can adapt through natural selection or acclimate to novel environmental conditions, I combined observational field data, greenhouse experiments, and spatial modeling to quantify V. americana reproduction at local to regional scales, evaluate evidence of local adaptation and acclimation to environmental stress, and assess the extent to which high levels of connectivity in a V. americana-dominated landscape can absorb environmental stress.I quantified reproduction at 15 sites in the Chesapeake Bay and 14 sites in the Hudson River, with sites in each geographic region spanning the portion of the salinity gradient in which V. americana grows (0-12 ppt). Numbers of inflorescences, sex ratios, and distances among male and female inflorescences varied greatly across latitude and along salinity gradients. Hudson V. americana had fewer inflorescences across two sampling seasons than Chesapeake Bay V. americana but delayed phenology, skewed sex ratios, and large distances among males and females relative to the Chesapeake Bay were more pronounced in 2018. In 2018, warmer spring and summer water temperatures in the Chesapeake coincided with our findings of higher flowering, fruiting, and potential for pollination at the three Chesapeake sites that served as means of comparison to the Hudson. By contrast, in 2020 Hudson plants were larger and produced more inflorescences in July than Chesapeake plants produced in June, indicating that the regional difference in phenology may be smaller than our hypothesis of approximately 23 days, although it is difficult to estimate how much smaller. We attribute this result to sites in the Hudson – mainly those in the tidal-fresh zone of the river – being highly responsive to unusually warm 2020 spring water temperatures. But not all sites experienced this warmth. The tidal-saline zone of the Hudson and the non-tidal zone of the Chesapeake had the fewest flowers and fruits of either region, likely due to the synergistic effects of cold temperatures and high salinity and turbidity in the former and fast currents in the latter inhibiting growth and reproduction. Through greenhouse experiments evaluating growth and reproduction of Chesapeake and Hudson V. americana grown in different salinity conditions, we found evidence of one-way local adaptation in plants sourced from brackish waters of both the Chesapeake and Hudson. In the first experiment (parental-generation), brackish-source plants demonstrated phenotypic buffering, a stress-induced version of phenotypic plasticity. When exposed to three salinity treatments (0 ppt, 6 ppt, and 12 ppt) applied after plants had sprouted, brackish-source plants buffered the effects of salt stress via increased vegetative growth in the form of many ramets and turions at the cost of small stature. By contrast, plants sourced from fresh waters of both regions grew tall in fresh water, but photosynthetic leaf material declined from the time of salt application (June) to the end of the experiment (September). The most severe salinity treatment, 18 ppt, was lethal to most individuals regardless of source habitat. Unfortunately, neither phenotypic buffering nor phenotypic plasticity sensu stricto was carried over via transgenerational plasticity (TGP), when turions were exposed to 12 ppt immediately upon planting (offspring generation). This early-development salt exposure proved lethal for some individuals and sublethal (had a negative effect on growth but did not result in mortality) for others, with turions either failing to sprout or growing a single shoot that was minuscule in stature. Parental-generation salt exposure only exacerbated these offspring effects, producing a non-adaptive TGP effect, resulting in even lower chance of sprouting, higher chance of mortality, and smaller stature. Evidence of local adaptation and acclimation to salinity only when exposure begins later in development suggests that populations have potential for resilience to saltwater intrusion (movement of saline water into fresh water) only if salinities do not remain elevated during the time of early plant development (spring/early summer) and across multiple seasons. In the event of prolonged salinity stress, much habitat (~10,000 hectares) that is currently mesohaline (5-12 ppt) but within the range of tolerance for V. americana will become unsuitable. In our spatial model of SAV persistence in the V. americana-dominated Upper Chesapeake Bay, high connectivity and high probability of SAV presence were found not only in the freshwater head of the Bay, but also in mesohaline (5-12 ppt) and oligohaline (0.5-5 ppt) waters near Middle River. Persistence of predominantly freshwater aquatic macrophytes in Middle River suggests that either 1) plants are locally adapted to brackish waters or 2) existing connectivity buffers the stress of low-quality habitat. Excess nitrogen, an anthropogenic environmental stressor that remains at high levels in Baltimore Harbor and other tributaries, was correlated with a decreased probability of SAV presence in the southern portion of our study area. As expected, low nitrogen, low salinity, and high landscape connectivity at the head of the Bay coincided with the highest predicted probabilities of SAV presence, particularly in the core of the one of the largest SAV beds in the entire Chesapeake Bay, the Susquehanna Flats.
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    Quantifying the impacts of climate-smart farming practices for improved management and long-term carbon storage
    (2023) Boniface, Helen S; Tully, Katherine L; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Within agricultural production there is tension between feeding a rapidly growing population and conserving the finite resources at the foundation of our agroecosystems. Fortunately, in recent decades there has been a growing focus on farming practices that promote long-term soil health, land productivity, and resilience to climate change. The term ‘conservation agriculture’ encompasses practices that 1) promote minimum soil disturbance, 2) maintain permanent soil cover, and 3) diversify plant species. This research evaluated several conservation agriculture practices for their ability to deliver desired agroecosystem services across the Northeastern US. In the first study, a cover crop mixture field experiment was implemented in seven states to evaluate how climatic, edaphic, and management conditions affected the performance of cover crop bicultures that included species with varying functional traits. Seeding rate recommendations for mixtures are typically developed at the regional level, thus cover crop performance is highly variable due to site-level conditions and competition among species. Our results indicated that expected spring growing degree days and baseline soil fertility (i.e., inorganic N) are the most significant variables to consider when designing site-specific cover crop mixtures. The second study assessed the effects of long-term management on soil organic carbon (SOC) dynamics in mid-Atlantic grain cropping systems. At the time of sampling, five unique systems (two conventional, three organic) had been continuously managed for 25 years, representing a range of tillage and fertility practices and rotational complexities. Results showed SOC loss in all systems over time regardless of management, likely because of high baseline SOC stocks from long-term perennial forage production prior to research plot establishment. However, cropping systems that best maintained SOC over time included management with minimal soil disturbance, frequent manure inputs, and/or greater rotational diversity through perennial cropping or cover cropping. Both studies increase our understanding of the ability of specific conservation practices to support agroecosystem biodiversity, long term soil health, and potential carbon sequestration.
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    (2023) Schulenburg, Alison Nicole; Tully, Kate; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Rising sea levels, storms, and perigean spring tides push saltwater into coastal agricultural fields. This phenomenon, known as saltwater intrusion, alters nutrient cycling and damages crop yields. As sea levels continue to rise, saltwater intrusion will only worsen, with devastating consequences to agroecosystems along the coast of the Chesapeake Bay. Researchers and farmers alike are looking for solutions to adapt to and mitigate the effects of saltwater intrusion. Landowners may respond by altering their management practices. Farmers may 1) adapt by planting a salt-tolerant crop, 2) attempt to remediate soils with trap crops, 3) restore native marsh grasses, or 4) abandon fields altogether. My project investigates the survival of different crops and plant treatments under saltwater-intruded conditions and the potential for these plants to survive and to remove excess nutrients (e.g. sodium and phosphorus) from the soil, with the overall goal to benefit both the farming community and water quality in the Chesapeake Bay. Results from this study will help inform new management practices to increase soil health and maintain crop yields. Finally, the goal of this work is to guide local best management practices and potential easement opportunities for landowners facing saltwater intrusion, and ultimately determine optimal strategies for climate resilience.
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    (2023) Boushell, Stephen Carl; Hu, Mengjun; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Fungicide resistance is a limiting factor in sustainable crop production. Despite the wide adoption of general resistance management strategies by growers, the recent rate of resistance development in important fungal pathogens is concerning. In this study, Botrytis cinerea and the high-risk fungicide fenhexamid were used to determine the effects of fungicide dose, tank mixture, and application timing on resistance selection across varied frequencies of resistance via both detached fruit assays and greenhouse trials. The results showed that application of doses lower than the fungicide label dose, mixture with the low-risk fungicide captan, and application post-infection seem to be the most effective management strategies in our experimental settings. In addition, even a small resistant B. cinerea population can lead to a dramatic reduction of disease control efficacy. Our findings were largely consistent with the recent modeling studies which favored the use of the lowest possible fungicide dose for improved resistance management.
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    RE-RO(O/U)TING: Reconfiguring mobilities and materialities through the design of a green-blue infrastructure corridor in Baltimore, Maryland
    (2022) Martin, Bryn; Ellis, Christopher; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This thesis engages with Ecological Urbanism through a literature review and design project. Through a literature review which reads ecological urbanism with other contemporary social theory, the thesis raises a question: how might an approach centering the materiality of landscape and its relation to mobility inform the interdisciplinary work of translation and interpretation which is central to ecological urbanism? This approach is examined through a design project examining the landscape of the lower Jones Falls, a small, culverted urban river. The project profiles some of the past and present mobilities and materialities shaping this urban environment. These observations inform a design project envisioning a daylighting of the culverted Jones Falls as a focal intervention in the reimagination of an urban expressway corridor as a twenty-first century ecological mobility corridor: a landscape of green and blue spaces, ecological infrastructure multimodal streetscapes, and a reinvigorated public realm.
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    (2022) Malzahn, Aimee Alyssa; Qi, Yiping; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In order to advance plant biology and speed up crop breeding, researchers have used genome engineering tools in their research. Genome engineering with CRISPR has revolutionized agriculture by providing an easy, fast, and accessible tool to induce desirable mutations. This thesis works on addressing problems in the application of CRISPR for plant genome engineering. CRISPR systems are adopted from bacterial immune systems and consists of a Cas endonuclease and a guide RNA (or crRNA). Cas variants have different characteristics and exploring natural variants can provide systems with enhanced or new applications. The first aim in this thesis is to demonstrate novel LbCas12a for genome editing in Arabidopsis. To overcome the temperature sensitivity of LbCas12a, a heat treatment regime was developed. In order to expand LbCas12a use beyond genome editing, a transcription repression system was developed and used successfully for multiplexed repression of two homologs of EDS1. Two crRNA processing systems were compared, and results suggest that either can be used successfully in Arabidopsis. The second aim is to improve Cas9 and Cas12a editing outcomes by creating Cas-effector fusions. Cas9 and Cas12a were fused with six different exonucleases and compared at three targets in rice protoplasts. Several Cas-exonuclease fusions resulted in an increase in editing efficiency and the production of larger deletions. The Cas-exonuclease fusions’ editing efficiency differed between Cas9 and Cas12a, along with the deletion profile. Additionally, chromatin modulating peptides were fused to Cas9, which resulted in higher editing efficiency without altering deletion profiles. These engineered Cas proteins can be used to create unique editing outcomes, and paired with an increased editing efficiency, could be used to target difficult-to-edit target sites for gene knockout and cis-regulatory elements for fine-tuning gene expression. In summary, this work explored new Cas variant LbCas12a, developed multiplex gene repression systems, and compared engineered fusion Cas9 and Cas12a proteins for increased editing efficiency and larger deletions. The developed and improved CRISPR systems expand the number of available targets, improve efficiency, demonstrate novel editing outcomes, and enable multiplexed transcriptional regulation in plants.
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    (2022) Sretenovic, Simon; Qi, Yiping; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Earlier genome editing technologies were developed based on programmable nucleases including zinc finger nucleases (ZFN) and transcription activator-like effector nucleases (TALEN), both requiring tedious protein engineering. By contrast, clustered regularly interspaced short palindromic repeats (CRISPR) systems, such as CRISPR-Cas9, has revolutionized the genome editing field in the past decade due to ease of guiding Cas9 endonuclease to the target site by programmable guide RNAs. However, not every target site can be edited due to Cas9 endonucleases’ recognition of so-called protospacer adjacent motif (PAM) when binding to the target site. For example, the PAM for the widely used SpCas9 is NGG (N=A, C, T or G). This drastically limits targeting scope in the genomes. Thus, researchers have developed engineered Cas9 variants recognizing more relaxed PAMs and tested them in mammalian cell lines. Repair of Cas9 endonuclease-induced double strand breaks through non-homologous end joining (NHEJ) DNA repair pathway typically generates unspecified insertions and deletions, which is a missed opportunity for introducing precise edits. To confer precise genome editing, CRISPR-Cas9 derived base editors and prime editors have been developed. In this work, expanding the plant genome editing scope with engineered Cas9 variants, improving precise cytosine and adenine base editing in plants as well as demonstrating prime editing in plant cells were pursued. The technologies were tested in the model crop, rice, in transiently transformed protoplasts and stably transformed T0 lines. Findings suggest that engineered Cas9 variants can drastically expand the targeting scope for targeted mutagenesis and base editing in plants. Additionally, newer genome editing technologies such as base editors and prime editors can be applied in plants to achieve precise genome editing with varying efficiencies. These validated and useful CRISPR-Cas9 genome editing toolkits have been deposited to the public vector depository, Addgene. Adoption of these genome editing technologies by plant scientists and breeders will enable basic research discoveries and accelerate breeding of next generation crops, ensuring global food security amidst climate change and increasing global population.