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The connection between nature and well-being has been recognized across cultures for centuries. One way in which people have facilitated this connection over the years has been through their interactions with plants and the practice of horticulture. Research over the years has further substantiated a connection between horticultural practices and overall well-being. However, a significantly disproportionate amount of this research has been conducted within the field of clinical psychology, despite the notable clinical implications. The current dissertation aims to address this gap in the current literature by exploring this connection from the lens of clinical psychology. More specifically, the current work outlines an extensive review of current, relevant literature, introduces the concept of therapeutic horticulture, and then conceptualizes therapeutic horticulture through various psychotherapeutic theoretical perspectives. Moreover, the current work aims to grow beyond the scope of the current dissertation to inform a subsequent book to define core competencies, standards, and guidelines for the use of therapeutic horticulture within the field of clinical psychology. Given this, the current dissertation is formatted as a formal book proposal and three sample chapters, which will then be submitted for publication.

Committee: Theodore Ellenhorn PhD (Committee Chair); Barbara Belcher-Timme PsyD (Committee Member); Katherine Evarts PsyD (Committee Member) Subjects: Clinical Psychology

8. Ertle, John Tipburn Management Through Controlled Environment for Indoor Vertical Farm Lettuce Production

Doctor of Philosophy, The Ohio State University, 2023, Horticulture and Crop Science

Indoor vertical farming has become increasingly popular in the United States due to the ability to grow fresh produce year-round. However, among other challenges to indoor farmers, is the issue of lettuce (Lactuca sativa) tipburn, a localized calcium deficiency disorder that causes marginal necrosis of leaves. Tipburn can cause significant economic losses and decrease the quality of the crop. Indoor farms generally encounter tipburn due to environmental conditions limiting transpiration that reduces supply of calcium to young, expanding leaves. During fast growth of lettuce, calcium supply is unable to meet the demand of growth, resulting in the deficiency. Therefore, evaluated tipburn risk under selected environmental conditions to induce tipburn and then examined two different lighting methods to reduce the risk of tipburn. We found that tipburn severity of ten commercial lettuce cultivars varied widely. However, those cultivars that had been developed specifically for indoor production had lower rates of tipburn than those recommended for outdoor cultivation or both indoor and outdoor production. Morphology or leaf color had no relationship with tipburn risk. Further, we found that average tissue calcium concentrations of inner leaves were not associated with shoot fresh mass or tipburn severity between cultivars. Therefore, shoot biomass or leaf calcium concentration is not indicative of tipburn risk. To develop alternative strategies that reduce tipburn of lettuce, we applied a reduced daily light integral (DLI) during the fast-growing stage of lettuce at the end of cultivation (final 12 d of 28-d production). This strategy resulted in less tipburn due to lower light limiting the yield of lettuce. For one highly tipburn-sensitive cultivar, we found that limiting yield under the lowest end-of-production DLI treatment reduced tipburn severity enough to increase marketable biomass. Therefore, reduced end-of-production DLI has the potential to increase revenue cont (open full item for complete abstract)

Committee: Chieri Kubota (Advisor); Leah McHale (Committee Member); Matthew Kleinhenz (Committee Member); Darren Drewry (Committee Member); Uttara Samarakoon (Committee Member) Subjects: Agriculture; Horticulture

9. Ludmer, Dana Web-based therapeutic horticulture intervention: An online program development study

Psy. D., Antioch University, 2022, Antioch New England: Clinical Psychology

The pandemic has become a nationwide psychological trauma, posing a serious mental health risk in the United States. As the pandemic increases social disconnection and depression, amongst other psychological concerns, the need for accessible therapeutic interventions has become imperative. The purpose of this dissertation was to evaluate the interest and preferences in a web-based therapeutic horticulture intervention for connectedness and well-being. This study utilized a mixed methods approach, including both qualitative and quantitative data collection and analysis. A needs assessment surveyed American Horticulture Therapist Association (AHTA) members as well as gardening hobbyists. Quantitative data was evaluated through descriptive statistics, while qualitative data was evaluated through a thematic analysis. The results indicated that there is an interest in the development of an online gardening resource and indicated directions for such a development. Directions included the importance of navigational ease and facilitation to increase likelihood of participation. Additionally, it emphasized the importance of previewing the website before enrollment. Results of the needs assessment were considered in the proposal of an initial prototype of the online gardening resource. The primary user flow of the website is detailed, as well as a plan to launch the web-based therapeutic horticulture intervention and future opportunities for research.

Committee: Theodore Ellenhorn Ph.D. (Committee Chair); Katherine Evarts Psy.D. (Committee Member); Gina Pasquale Psy.D. (Committee Member) Subjects: Clinical Psychology

10. Mattingly, Kali Hybridization and whole genome duplication as drivers of biological invasions

Doctor of Philosophy, The Ohio State University, 2021, Evolution, Ecology and Organismal Biology

Humans engineer their environments by transporting species around the planet. In a new environment, most introduced species will perish, but a small proportion can become invasive, spreading widely and impacting their environments. My dissertation explores how evolutionary processes shape invasive species. I studied two mechanisms of invasive species evolution that can induce rapid evolutionary change: hybridization (mating between genetically distinct individuals) and whole genome duplication (WGD, when offspring inherit an extra set of chromosome pairs). In Chapters 1 and 2, I describe experiments with members of the model plant genus Arabidopsis differing only in genome size and status as either parent or hybrid, effectively isolating the independent effects of WGD and hybridization on traits. I grew plants together under controlled conditions and measured traits and phenotypic plasticity (the change in trait values across imposed environmental gradients). For the handful of traits and gradients in which WGD shifted plasticity values, WGD consistently increased plasticity (Chapter 1). This study provides the most controlled experimental evidence to date in support of the hypothesis that WGD increases plasticity, a hypothesis invoked to help explain how WGD has driven evolution. In contrast to WGD, I found that hybridization produced larger effects on both mean traits and plasticity (Chapter 2). This experiment is the first to fully isolate hybridization and WGD effects on plasticity. In nature, genetic and trait variation provide the raw material allowing invasive species to initially prevail in and, potentially, adapt to the introduced environment. I examined patterns of variation related to hybridization and WGD for two invasive plant systems (Chapters 3 and 4). Chapter 3 focuses on purple loosestrife (Lythrum salicaria), a well-studied species for which other authors have documented post-introduction changes in traits and genetics. A little-studied, mo (open full item for complete abstract)

Committee: Stephen Hovick (Advisor); Alison Bennett (Committee Member); Andrea Wolfe (Committee Member); Kristin Mercer (Committee Member); Amanda Simcox (Committee Member); Robert Klips (Committee Member) Subjects: Biology; Botany; Conservation; Ecology; Evolution and Development; Genetics; Horticulture; Morphology; Organismal Biology

11. Cordero-Irizarry, Patricia Soil Carbon as A Soil Quality Indicator of A Fruit Orchard In Puerto Rico

Master of Science, The Ohio State University, 2021, Environment and Natural Resources

Soil quality is defined as the soil's capacity to function within natural or managed ecosystems to sustain plant-animal-human health. It can be inferred from the quantification of soil properties which can be combined into a soil quality index (SQI). An SQI is a value that combines soil physical, chemical, and biological characteristics and scores the soil's “fitness to function”. Soil management practices (SMP), which differ depending on the landholder's agenda, can increase or decrease soil carbon (C) storage, which is an important parameter used for SQI calculation. Therefore, the objectives of this study were: (1) to evaluate the impact of SMP on physicochemical properties in an avocado orchard (AVO) and a tropical pumpkin/bean (TPB) plot and (2) to develop an SQI for each system. The study was conducted in the Juana Diaz Agricultural Experimental Station located in the south-central coast of Puerto Rico and the predominant soil series was San Anton. Both systems scored 0.55 on the 0 to 1 SQI scale, suggesting that higher soil C content does not imply an improvement in soil physicochemical quality. However, reduced tillage operations and natural ground cover have a positive impact on soil quality indicators, but not on soil physicochemical quality itself for this study. Future research priorities should be directed towards the evaluation of soil taxonomical characterization on soil quality and determine its significance if any.

Committee: Rattan Lal Dr. (Advisor); Jeffory Hattey Dr. (Committee Member); Roger Williams Dr. (Committee Member); David Sotomayor Dr. (Committee Member) Subjects: Agriculture; Agronomy; Environmental Studies; Horticulture; Soil Sciences

12. Nordstedt, Nathan Isolation and characterization of novel bacterial strains to alleviate abiotic stress in greenhouse ornamental crops

Doctor of Philosophy, The Ohio State University, 2021, Horticulture and Crop Science

The production of greenhouse ornamental crops relies on extensive inputs of water and chemical fertilizers to produce high-quality plants for consumers. These inputs are both economically and resource expensive, leading to increased concerns of sustainability. In addition, ornamental crops can encounter water and nutrient stress throughout their life span, impacting their health, quality, and resiliency for consumers. Water stress decreases the health and quality of horticulture crops by inhibiting photosynthesis, transpiration, and nutrient uptake, contributing to a reduction in plant size and flower number. The lack of bioavailable nutrients for plant uptake negatively impacts plant metabolism, influencing different aspects of plant growth and development. The effect of both abiotic stresses decreases the salability of crops at retail and can impact consumer success in the landscape. Therefore, it is important that the horticulture industry has sustainable tools to decrease resource-intensive inputs while also increasing plant abiotic stress tolerance, without sacrificing crop quality. Plant growth promoting bacteria (PGPB) can increase plant growth under water and nutrient-limiting conditions by enhancing stress tolerance and increasing nutrient availability, uptake, and assimilation by plants. PGPB colonize their plant host and can stimulate plant growth and stress tolerance through a myriad of different mechanisms. The identification of PGPB for greenhouse ornamental crops will contribute to the formulation of commercial productions that can be implemented into greenhouse production systems for the sustainable production of high-quality and resilient crops. This work outlines the identification, evaluation, and characterization of PGPB for greenhouse ornamental crops subjected to water stress and low-nutrient conditions. A core collection of 45 bacterial isolates was utilized to develop a high-throughput approach for the selection and evaluation of PG (open full item for complete abstract)

Committee: Michelle Jones (Advisor); Christopher Taylor (Committee Member); Ye Xia (Committee Member); Jyan-Chyun Jang (Committee Member) Subjects: Horticulture; Plant Biology; Plant Pathology

13. South, Kaylee Improving abiotic and biotic stress tolerance in floriculture crops

Doctor of Philosophy, The Ohio State University, 2020, Horticulture and Crop Science

An intensive production system is used to produce greenhouse floriculture crops, marketed for their flowers and attractive foliage. Chemical, environmental, and cultural methods are used to manage biotic and abiotic stresses during production. Additional tools are needed by growers because of growing concerns around the negative impact of plant production on humans and the environment. The objective of this research was to evaluate potential tools to improve floriculture crop resilience under stress during production and post-production. Botrytis cinerea causes disease in most major greenhouse crops and is resistant to several fungicides. Additional control methods, like plant growth promoting bacteria (PGPB) that can improve plant performance by increasing plant resilience to stress are needed. A collection of 60 bacterial strains was evaluated in a dual culture assay and an initial greenhouse trial with Petunia × hybrida `Carpet Red Bright' to identify strains for the biocontrol of B. cinerea. Daily flower disease severity ratings were used to select seven strains that were evaluated in the validation greenhouse trial. Three Pseudomonas strains were selected for the greatest reduction in B. cinerea infection. The efficacy of PGPB and the plant's susceptibility to B. cinerea were affected by fertilization. Petunia × hybrida `Carpet Red Bright' was treated with bacteria or a commercial biocontrol product and fertilized with synthetic chemical or organic fertilizer at a low or high rate. Measured plant growth and flower disease severity revealed that plants with the high rate synthetic fertilizer were the largest and had the lowest disease severity. Reduction of disease severity varied between bacterial and fertilizer treatment combinations. Plants treated with one bacterium had reduced disease severity at the high rate synthetic chemical fertilizer but not at the low rate organic fertilizer. Specific fertility programs provide crops with needed macro and mi (open full item for complete abstract)

Committee: Michelle Jones (Advisor); David Francis (Committee Member); Francesca Hand (Committee Member); Pablo Jourdan (Committee Member); Matthew Kleinhenz (Committee Member) Subjects: Agriculture; Horticulture

14. Gillespie, Daniel Effects of Low Nutrient Solution pH on Hydroponic Leafy Green Plant Growth, Nutrient Concentration of Leaf Tissue, and Pythium Zoospore Infection

Master of Science, The Ohio State University, 2019, Horticulture and Crop Science

In recent years, the increased demand for locally grown produce and outbreaks of E. coli linked to leafy greens has led to hydroponic leafy green production in controlled environments becoming a viable addition to the fresh produce food supply. Prevention of plant pathogen introduction in hydroponics is critical, as effective control agents for root diseases of edible crops are limited and may not be registered for use in greenhouses or indoors. This study examined lowering nutrient solution pH as a new management strategy to mitigate the risk of oomycete root disease incidence without negatively influencing plant growth. Although pH below 5.0 has been shown to negatively affect oomycete pathogen growth and reproduction, hydroponic nutrient solution is typically maintained within pH 5.5-6.5, as plants tend to exhibit growth inhibition outside of this range. Nevertheless, growth inhibition can typically be attributed to pH-dependent factors affecting nutrient uptake and availability, which may be mitigated if precautionary measures are considered. We hypothesized that if plants can be grown in pH below 5.0, the risk of oomycete disease incidence may be reduced. As first steps towards the development of a new nutrient solution management strategy, we determined if adjusting micronutrient concentrations in nutrient solution based on reported availability levels were effective in mitigating nutrient disorders and plant growth inhibition typically experienced at low pH. Basil and spinach plants were grown in deep-water hydroponic systems with pH maintained at 4.0, 4.5, 5.0, or 5.5. Two nutrient solutions (with and without micronutrient adjustments) were applied at each pH level, where concentrations of copper, zinc, manganese, and boron were decreased by one-half and molybdenum concentration was doubled in the adjusted solution. To our surprise, even though most elemental concentrations of leaf tissue decreased with decreasing pH, basil plant growth was not affected by (open full item for complete abstract)

Committee: Chieri Kubota PhD (Advisor); Sally Miller PhD (Committee Member); Michelle Jones PhD (Committee Member) Subjects: Agricultural Chemicals; Agricultural Economics; Agricultural Education; Agriculture; Horticulture; Plant Pathology