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Phosphorus (P) is one of the three major macronutrients that plants need to grow and survive. When P is scarce, plants utilize a network of characterized responses known as the Phosphate Starvation Response (PSR) to remobilize internal stores of P as well as external P from soil. Emerging evidence shows the PSR is regulated by a specialized group of secondary messenger molecules, inositol pyrophosphates (PP-InsP). PP-InsPs and their precursors, inositol phosphates (InsPs), are important for plant abiotic stress responses, hormone signaling, and other stress responses. While PP-InsPs are critical for plant survival, much about the roles of PP-InsPs and how they are regulated remains to be understood. Further, the enzymes responsible for the synthesis of PP-InsPs in plants have been recently discovered; however, not much is known about the enzymes that degrade PP-InsPs in plants. The goal of the work presented herein is to understand critical aspects of the PP-InsP signaling in plants and leverage this information into a P phytoremediation strategy. To achieve this, I have investigated a group of PP-InsP phosphatases and assessed long-term impacts of depleting PP-InsPs in two plant species, Arabidopsis thaliana (Arabidopsis) and Thlaspi arvense (Pennycress). Exploring the impact of plant PP-InsP phosphatases has allowed me to explore critical aspects of PP-InsP sensing that show great promise for informing P remediation strategies. / Doctor of Philosophy / The Phosphorus (P) crisis presents a major challenge to food security. While Phosphorus (P) is critical for crop growth, P is a nonrenewable and increasingly limited resource. Our global population is fed at the expense of the remaining mineable P reserve, which may be depleted in as early as 30 years. Further, fertilizer runoff from farmland and urban areas poses a dangerous problem as increased nutrients in watersheds toxifies our water supply and aquatic ecosystems. Time is running out to preserve our P supply. New and innovative strategies that reduce fertilizer inputs and watershed pollution are key to securing the global food supply and protecting the environment. Emerging evidence shows plants sense and respond to P using signaling molecules known as inositol pyrophosphates (PP-InsPs). My work and that of others are key in showing that alteration of the levels of PP-InsPs can decrease plant P dependency or cause plants to hyperaccumulate P. Understanding how plants are able to sense, respond, and acquire P is crucial to inform future P phytoremediation strategies to secure global food security.

Just and equitable responses to the disparate impacts of climate change on communities and individuals throughout the world are at the heart of the concept of climate justice. Commodification, in the context of my research, is the process of monetizing nature and livelihoods for the purpose of surplus accumulation and profit maximization. In this study, my aim was to contextualize the concepts of climate injustice, disaster capitalism, and the commodification of lives and livelihoods in the specific setting of disaster vulnerability in southwest coastal Bangladesh. By conducting a case study in Kamarkhola and Sutarkhali regions of southwest coastal Bangladesh, I utilized discourse analysis and content analysis of livelihood interviews, semi-structured interviews, and policy documents to demonstrate the conceptual interrelation among global climate change, climate injustice, disaster capitalism, and capitalist expansion in environmentally precarious areas. I argue that in Southwest Coastal Bangladesh, the vulnerability to disasters stems from a complex and multifaceted layer of social hierarchies and inequalities, entwined with factors such as class and power relations. I also argue that Inequalities in the political, economic, and social realms have a key role in imposing vulnerability on disadvantaged people living in ecologically vulnerable areas. The perpetuation of inequality is sustained by the expansion and accumulation of capital through the dispossession and exploitation of natural resources. The existing approaches to climate change adaptation in the southwest coastal region of Bangladesh are deeply entrenched in neoliberal capitalism. The introduction of neoliberal economic policies, such as the privatization of state lands and the promotion of export-oriented aquaculture, created favorable conditions for capitalist expansion in environmentally vulnerable places through "accumulation by dispossession."

Cover crops are widely planted in the mid-Atlantic region for their environmental and agronomic benefits, but incomplete or delayed termination can lead to cover crops becoming weeds in the subsequent cash crop, known as volunteers. Studies were conducted from 2020-2022 to evaluate the effect of four commonly grown cover crop species, winter wheat (Triticum aestivum L.), cereal rye (Secale cereal L.), hairy vetch (Vicia villosa Roth), and rapeseed (Brassica napus L.), and four termination timings; 28, 14, 5, and 1 days before corn planting (DBP). Results indicated volunteerism was only an issue with rapeseed. Delaying rapeseed termination resulted in 0, 5, 12, and 22 volunteer plants m-2 at 28, 14, 5, and 1 DBP in corn. In order to manage these rapeseed volunteers, herbicide evaluations were conducted and indicated that atrazine, isoxaflutole, metribuzin, and pyroxasulfone resulted in 92-94% control when applied preemergence. Similarly, atrazine and glyphosate provided 99% rapeseed control and glufosinate resulted in 89% control when applied postemergence. Therefore, volunteers can easily be controlled with commonly used herbicides in corn. Studies were also conducted to evaluate the benefits of these cover crops, which have the potential to overcome the aforementioned risks. Results indicate that hairy vetch produced the most biomass and provided greater control of summer annual grasses, small-seeded broadleaf and large-seeded broadleaf weeds than other cover crops. Biomass accumulation and extent of weed control increased with delaying cover crop termination. Corn yield was greatest following hairy vetch and was least in rapeseed plots. Termination of cover crops 14 DBP planting increased corn yield by 12%; whereas termination at 1 DBP decreased corn yield by 15% as compared to no cover crop-no till plots. Effective termination of cover crops is an important management consideration and information on termination efficiency can help in devising management plans. In order to assist managers by evaluating cover crop termination efficiency, studies were conducted to evaluate selective and non-selective herbicides and a roller crimper for correlating vegetative indices with visible termination efficiency. Among vegetative indices, the Green Leaf Index had the highest Pearson correlation coefficient for wheat (r = -0.79, p = <0.0001) and cereal rye (r = -0.80, p = <0.0001) with visible termination efficiency. Whereas, for rapeseed, Normalized Difference Vegetation Index (NDVI) had the highest correlation coefficient (r = -0.66, p = <0.0001). However, for hairy vetch none of the vegetative indices correlated significantly with visible termination efficiency. While further research is necessary, remote sensing technologies may help in devising management plans by increasing crop scouting efficiency. / Master of Science in Life Sciences / Cover crops reduce soil erosion, leaching of soil nutrients in the water bodies, and provide benefits like weed suppression and improving the cash crop yield. Cover crops are generally planted in fall after the harvest of cash crop and are killed (terminated) before or after planting of next cash crop in the spring. Cover crop plants can also become weedy when they grow as volunteer plants in cash crops and if not terminated effectively. Therefore, effective termination of cover crops is also an important management consideration. Keeping these aspects in view, field experiments were conducted to evaluate different cover crops, winter wheat, cereal rye, hairy vetch, and rapeseed and four termination timings, 28, 14, 5, and 1 days before corn planting (DBP) for biomass accumulation, weed control, and impact on corn yield. Among cover crops, hairy vetch was found to be the best in terms of biomass production, weed control, and improving corn yield, whereas rapeseed had least biomass accumulation and reduced corn yield. Among termination timing, 1 and 5 DBP resulted in the most biomass production and weed control, but corn yield was greatest when terminated at 14 DBP. Delaying rapeseed termination from 28 DBP to 14, 5, and 1 DBP increased volunteer rapeseed in corn by 5, 12, and 22 plants m-2. Preemergence (PRE) and postemergence (POST) herbicides were evaluated for volunteer rapeseed control in corn. Among preemergence (PRE) herbicides, mesotrione, rimsulfuron and flumioxazin provided more than 95% volunteer rapeseed control, whereas atrazine, isoxaflutole, metribuzin, and pyroxasulfone provided 92-94% control. Among postemergence (POST) herbicides, atrazine and glyphosate provided 99% visible control of rapeseed, followed by glufosinate (89%). Various selective and non-selective herbicides were also evaluated for the termination of wheat, cereal rye, hairy vetch, and rapeseed. Non-selective herbicides like glyphosate, glufosinate and paraquat were found more effective for termination of cover crops as compared to non-selective herbicides. Vegetative indices (VI) were evaluated and correlated with visible termination efficiency (ground truth data) and found that VI can be used for estimating termination efficiency and these estimates can help in devising plans for management operations. Among VI, Green Leaf Index had the highest correlation coefficient for wheat and cereal rye visible termination ratings. Whereas for rapeseed, Normalized Difference Vegetation Index (NDVI) had the highest correlation coefficient value. However, for hairy vetch none of the vegetative indices correlated significantly with visible termination efficiency. Overall, hairy vetch was found to be the best cover crop for biomass accumulation, weed control and corn yield improvement. Delayed termination of rapeseed plants resulted in infestation of volunteer rapeseed in corn and reduced corn yield. However, volunteer rapeseed plants can be effectively managed by effective termination and use of proper PRE and POST herbicides in corn. Furthermore, remote sensing-based VIs have shown potential to estimate cover crop termination efficiency.