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Publication Effect of Nano-Sulfur on Crop Productivity and Food Safety(2024-09) Sharma, SudhirThis study investigated the efficacy of nanosulfur compared to other sulfur forms in reducing heavy metal accumulation and toxicity in rice, soybean, and wheat. We also studied its potential use as a novel sulfur fertilizer. We found out that Nanosulfur (NS) soil amendment significantly alleviated arsenic (As) toxicity in rice as rice seedlings co-exposed to arsenite (AsIII) and NS showed substantial increases in growth and lowered As levels in roots, shoots, flag leaves, and grains. NS modulated gene expression related to As transport and sulfur assimilation and possibly reduced arsenite to the insoluble arsenic sulfide in the soil to reduce As bioavailability. Nanosulfur also effectively reduced silver nanoparticle (AgNPs) toxicity in soybeans as plants grown with NS+AgNP treatment exhibited better growth and less Ag accumulation in roots and shoots compared to AgNPs alone. In wheat, we tested different types of sulfur viz. bulk sulfur (BS), nanosulfur, ionic sulfur (IS), and stearic acid-coated nanosulfur (SA) as soil amendments to reduce cadmium (Cd). We found that particulate sulfur (BS, NS, SA) reduced soil pH and increased Cd accumulation, whereas ionic sulfur (sodium sulfate) did not lower soil pH as much, resulting in lower Cd accumulation in the plants. BS showed the most significant reduction in soil pH resulting in the most Cd accumulation. We also noted varietal differences with variety 'Louise' being more Cd-sensitive than 'Bobwhite'. As a novel sulfur fertilizer source in rice, NS application led to significant increases in biomass and grain yield compared to control and BS-treated plants. NS provided stable sulfate concentrations over time, enhancing its efficacy. In wheat, foliar applications of different sulfur forms positively influenced productivity but soil amendment with NS100 outperformed other treatments, improving agronomic and physiological traits. Similarly, soybean plants treated with NS showed increased biomass, seed yield, and nutrient accumulation. Varietal differences were observed, with 'William 82' responding better to NS than 'Thorne', indicating the need for targeted strategies based on specific plant varieties. In conclusion, nanosulfur proves to be a valuable tool in mitigating heavy metal toxicity and enhancing crop productivity.Publication Hydrochars and Microplastics: Analysis of Their Effects on Plant Growth and Soil Health(2024-05) Khosravi, AnahitaThe nexus of soil health, crop productivity, and environmental contamination, especially from microplastics (MPs), presents a complex challenge in sustainable agriculture. This dissertation explores the effects of various biosolids on soil health and crop growth, with a focus on mitigating the risks of organic pollutants and MPs in agroecosystems. Three experimental studies were conducted to investigate the potential of raw and treated biosolids, including the development of hydrochars from sewage sludge (SS) and chicken manure (CM), and their impact on the growth of soybean and corn, as well as the presence and effects of MPs in fertilizers and soil. In the first experiment, hydrochars produced from SS and CM at two temperatures (125°C and 225°C) were compared with conventional phosphate fertilizer. Results indicated that low-temperature hydrochars significantly increased crop biomass and soil phosphate availability, potentially offering a sustainable alternative to traditional fertilizers. The lower temperature hydrochars improved dry biomass significantly, indicating their direct nutrient supply efficacy. The second study quantified MPs in organic fertilizers, revealing high variability in MP abundance and composition. Composts displayed between 13,600 to 61,850 MPs per gram, with the quantity and size distribution of MPs being influenced by the feedstock and treatment conditions. Notably, organic fertilizers contained the highest MP levels, emphasizing the urgency for monitoring and managing MP pollution in fertilizer inputs. The third experiment assessed the impact of polyethylene microplastics (PE-MPs) on lettuce growth in hydroponic and soil systems. Degraded PE-MPs were shown to have a more detrimental effect on plant health, affecting photosynthesis, respiration, and nutrient uptake. Metabolomic analysis revealed substantial shifts in vital plant metabolites, indicative of defensive responses and stress adaptation. These findings highlight the need for sustainable soil amendment strategies that consider environmental contaminants, like MPs, and their complex interactions with soil and plant systems. They call for a reevaluation of biosolid use in agriculture and stress the importance of treatment processes to mitigate potential risks. The research underscores the imperative of developing integrated solutions to enhance soil health, ensure food security, and protect ecosystems from emerging contaminantsPublication ROLE OF GLUTATHIONE DEGRADATION PATHWAY GENES FOR GLUTATHIONE HOMEOSTASIS AND TOXIC METAL TOLERANCE IN PLANTS(2024-02) Singh, GurpalThe study explores plant defense against toxic metal stress, particularly focusing on glutathione (GSH) homeostasis via Œ≥-glutamyl cycle. GSH, a potent antioxidant, plays a central role in maintaining redox balance, defense responses, and nutrient reserves in plant cells. Understanding the regulation of GSH degradation via Œ≥-glutamyl cyclotransferases (GGCTs) and oxoprolinase (OXP1) is vital, especially under toxic metal stresses. Building upon prior research, which highlighted the role of AtGGCT2;1 in enhancing tolerance to arsenite (AsIII) toxicity in Arabidopsis, this study explores the contributions of two other GGCTs - AtGGCT1 and AtGGCT2;2, for their roles in GSH degradation and toxic metal tolerance. AtGGCT1 overexpression (OE) improves tolerance to arsenite (AsIII), cadmium (Cd), and mercury (Hg) by enhancing GSH degradation and subsequent recycling of constituent amino acids via the Œ≥-glutamyl cycle. Whereas AtGGCT2;2 OE primarily enhances Cd tolerance. ggct1 and ggct2;2 mutants showed improved growth on vi AsIII and Cd. Further, ggct1 mutants had decreased As, Cd and Hg accumulation in shoots, but the results for roots varied. No difference was noticed in toxic metal accumulation in OE lines, but the OE lines had relatively better Glu recycling, as indicated by labeled 15N-glutamte analysis. The results from Arabidopsis were successfully translated into Camelina sativa, a biofuel crop. An AtGGCT2;1 homolog from Camelina, CsGGCT2;1, was overexpressed in Camelina and the modified plants showed strong tolerance to AsIII with 40-60% reduced As accumulation in roots and shoots. Additionally, the research investigates the role of AtOXP1 in GSH homeostasis and Glu recycling under As and Hg stress. The oxp1 T-DNA mutants exhibit lower Glu levels and susceptibility to Hg, but not to AsIII. The AtOXP1 OE enhanced tolerance to AsIII and Hg by promoting Glu recycling, lower lipid peroxidation and reduced As and Hg accumulation. AtOXP1 OE lines had better growth under low N conditions relative to WT, indicating enhanced internal Glu recycling. The findings have broad implications for future agriculture, food security, and development of metal-resilient crops for cultivation of contaminated lands. By comprehending the intricate interactions between plant genes, heavy metals, and nitrogen assimilation, this research contributes to a safer and more sustainable food production system.