Theses and Dissertations at Montana State University (MSU)
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Item A computational study of a high-spin iron(I) complex for possible dinitrogen reduction to ammonia(Montana State University - Bozeman, College of Letters & Science, 2023) Pollock, Charlie Jeananne; Chairperson, Graduate Committee: Martin A. MosqueraA series of high-spin, low coordinate, paramagnetic iron complexes bearing a phenyltris((tert- butylthio)methyl)borate ligand were computationally modeled with density functional theory (DFT) and complete active space self-consistent field theory (CASSCF). The iron complexes examined in this research were inspired by nitrogenase, a naturally occurring, dinitrogen- fixating, iron-containing metalloenzyme. DFT and CASSCF offer a convenient way to explore reactions, complexes, and molecular orbitals without an immediate need to perform synthetic experiments. Our computational work can be used to guide synthetic efforts as well as urge future theoretical work in related research. DFT was utilized to compute two different thermodynamic properties: bond dissociation free energy (BDFE N-H) and Gibb's free energy. The conductor-like polarizable continuum model (CPCM) was applied to examine the solution phase of the system, and all BDFE and DeltaG values found were endothermic in tetrahydrofuran (THF). The methods, BP86 and BP86 ZORA, examined the gas phase of the system. The BDFE and DeltaG values calculated when using those two methods were largely inconsistent, which lead to the conclusion that the solution phase model is the most appropriate method for computing values of the dinitrogen complex ([Fe] 2(Mu-N 2)) and its related complexes. An N 2 vibrational mode was found (1915.30 cm -1) for [Fe] 2(Mu-N 2), which reflects a strongly coordinated dinitrogen bridge (Fe-N identical to N-Fe). Broken symmetry DFT (BSDFT) was used to examine the exchange coupling, which was found to have positive values (JAB =82.51 cm -1, 61.88 cm -1, 81.36 cm -1), and implied that [Fe] 2(Mu-N 2) is ferromagnetically coupled. Lastly, CASSCF and DFT were applied to plot and characterize certain molecular orbitals of [Fe] 2(Mu-N 2). The plotted and characterized molecular orbitals reflected moderate (DFT) to strong (CASSCF) covalent bonding between iron and dinitrogen. All this data reflected the synthetic plausibility of dinitrogen coordination to the bridged, Fe(I) complex ([Fe] 2(Mu-N 2)) that can be reduced through the dinitrogen cleavage mechanism.Item Influence of dose volume on nitrogen removal in a two stage vertical flow treatment wetland: Bridger Bowl ski area case study(Montana State University - Bozeman, College of Engineering, 2023) Brush, Kristen Onofria; Chairperson, Graduate Committee: Otto SteinTreating wastewater in remote locations does not require compromising the effluent quality discharged to the environment. A two-stage vertical flow treatment wetland (VF TW) with recycle meets this objective by removing high inputs of chemical oxygen demand (COD) and nitrogen (N) while requiring minimal maintenance and operator oversight. A 95.2 m 2 pilot scale VF TW at Bridger Bowl Ski Area, near Bozeman, MT, effectively treats the high strength domestic wastewater produced onsite. The partially saturated first stage of the VF TW removes influent COD and an unsaturated second stage nitrifies influent ammonium. Recycling second stage effluent to the first stage allows for nitrate removal by denitrification in the saturated zone of the first stage. Previous research indicated the system experiences near complete nitrification in the second stage and that total nitrogen removal is limited by denitrification in the first stage, potentially due to low organic carbon (COD) availability in the saturated zone. Therefore, the goal of the current study was to increase the COD:N ratio of the water entering the first-stage saturated zone by increasing the dose depth of influent (septic) water, high in COD, thereby reducing COD removal in the unsaturated layer. To evaluate denitrification performance a simplified stoichiometric process model accounted for both nitrate created and COD removed in the first stage unsaturated zone. During the 21-22 season, approximately 7 cm/day of septic water was applied to the first stage in either 1.2 or 2.5 cm doses. The larger doses showed enhanced nitrate removal efficiency in the saturated zone; however, a changing influent water quality may have supplemented efficiency improvement. During the 22-23 season, 12 cm/day of septic water was applied to the first stage in either 1 or 4 cm doses. During this experiment, influent water quality was the same, and the larger dose depths did not show enhanced nitrate removal. However, decreasing the septic dose depth increased first stage nitrification from 20 to 48% and COD removal from 77 to 82%. Throughout both experiments, system COD removal was > 95% (influent COD > 750 mg/L) and system ammonia removal was > 98% (influent NH 4 >160 mg/L).Item Natural variation in camelina nitrogen responses(Montana State University - Bozeman, College of Agriculture, 2023) Gautam, Shreya; Chairperson, Graduate Committee: Chengci Chen; Chaofu Lu (co-chair)Camelina (Camelina sativa L.Crantz) is an oilseed crop with the potential to be planted for biofuel production. It is crucial to select camelina genotypes with higher nitrogen use efficiency (NUE) so that the superior cultivar has higher crop productivity. To select genotypes of camelina that exhibit higher biomass yield and nitrogen use efficiency, two field experiments were conducted in 2021 and 2022 in Sidney, MT with different nitrogen regimes, low (unfertilized) and high (fertilized). Distinct projects were carried out, one of them emphasizing canopy area and normalized difference vegetation index (NDVI), and the other focusing on biomass yield and NUE. The experiments highlighted the response of camelina to nitrogen application and the variation among genotypes. The study identified canopy image analysis effectively differentiated the canopy size and growth rate of camelina genotypes under two nitrogen regimes, demonstrating the influence of nitrogen on camelina growth. The NDVI measurement proved to be useful in evaluating plant health and greenness, offering a time-saving and efficient approach. Additionally, some of the genotypes were identified that exhibited high canopy area, NDVI, and nitrogen use efficiency in both 2021 and 2022, providing potential for enhancing crop productivity. This study reveals the potential to use canopy area, NDVI for biomass yield and nitrogen use efficiency screening in camelina.Item Spatial patterns in soil depth and implications for offseason nitrogen dynamics in dryland wheat systems of central Montana(Montana State University - Bozeman, College of Agriculture, 2022) Fordyce, Simon Isaac; Co-chairs, Graduate Committee: Clain Jones and Craig Carr; Pat Carr, Clain Jones, Jed Eberly, Scott Powell, Adam Sigler and Stephanie Ewing were co-authors of the article, 'Exploring relationships between soil depth and multi-temporal spectral reflectance in a semi-arid agroecosystem: effects of spatial and temporal resolution' submitted to the journal 'Remote Sensing of environment' which is contained within this thesis.; Pat Carr, Clain Jones, Jed Eberly, Rob Payn, Adam Sigler and Stephanie Ewing were co-authors of the article, 'Spatiotemporal patterns of nitrogen mineralization in a dryland wheat system' submitted to the journal 'Agriculture, ecosystems, and environment' which is contained within this thesis.Shallow soils (< 50 cm) under dryland wheat (Triticum aestivum L.) production lose large amounts of inorganic nitrogen (N) to leaching. Crops grown in shallow soils may be more responsive to N fertilizer due to lower fertilizer recovery and suppressed mineralization, raising questions as to whether standard practices of N fertilizer rate determination can increase risks of leaching and groundwater contamination in these environments. Mineralized N can be a major nutritional supplement for wheat crops in dryland agroecosystems, so accurate estimates of mineralization inputs can have important economic and environmental implications. To assess the potential for suppressed N mineralization in shallow soils, we used spectral reflectance from up to three sensors (unmanned aerial vehicle, National Agricultural Imagery Program, and Sentinel 2) to spatially characterize soil depth on three fields in Central Montana (Chapter 2) and compared surface (0-20 cm) carbon and N cycling indices across soil depth classes (Chapter 3). Carbon dynamics were stable across depth classes while N mineralization was lower in the shallow class. Results confirm multispectral imagery as a valuable tool for non-destructively characterizing fine-scale spatial patterns in soil depth and corroborate previous findings of lower N mineralization in shallow soil environments. Given the potential for heightened fertilizer responsiveness due to lower mineralization in these environments, decision support systems for site-specific fertility management (e.g., variable rate fertilizer application) should assess the environmental consequences of leaching alongside the economic benefits of applied fertilizer rates which maximize responses of yield, quality and same-year net revenue.Item Water quality response to water and nitrogen movement through a semi-arid dryland agroecosystem in Montana, USA(Montana State University - Bozeman, College of Agriculture, 2020) Sigler, William Adam; Chairperson, Graduate Committee: Stephanie A. Ewing; Stephanie A. Ewing, Clain A. Jones, Robert A. Payn, E.N. Jack Brookshire, Jane K. Klassen, Douglas Jackson-Smith and Gary S. Weissmann were co-authors of the article, 'Connections among soil, ground, and surface water chemistries characterize nitrogen loss from an agricultural landscape in the upper Missouri River Basin' in the journal 'Journal of hydrology' which is contained within this dissertation.; Stephanie A. Ewing, Clain A. Jones, Robert A. Payn, Perry Miller and Marco Maneta were co-authors of the article, 'Water and nitrate loss from dryland agricultural soils is controlled by management, soils, and weather' submitted to the journal 'Agricultural ecosystems & environment' which is contained within this dissertation.; Stephanie A. Ewing, Scott D. Wankel, Clain A. Jones, Sam Leuthold, E.N. Jack Brookshire and Robert A. Payn were co-authors of the article, 'Drivers of denitrification across a semiarid agroecosystem revealed by nitrate isotopic patterns' which is contained within this dissertation.Humans have increased reactive nitrogen (N) on the planet by an order of magnitude over the past 150 years. Most of this reactive N is used for fertilizer to feed a growing population, but loss of N from cultivated soils threatens agricultural and environmental sustainability. Nitrate accumulated in soil from fertilization or decomposition of soil organic N (SON) may be lost via leaching, which can reduce soil fertility and compromise water quality. Nitrate concentrations commonly exceed human drinking standards in groundwater resources around the globe. In the Judith River Watershed (JRW) in central Montana, nitrate has been detected above the standard since the 1960s. This dissertation contributes to a more holistic understanding of the fate and transport of N in the JRW. An interdisciplinary team engaged with farmers in a participatory research project, making observations in soils, groundwater, and streams to characterize water and N movement. At the landform scale, 5 to 9 cm yr -1 of the 38 cm yr -1 mean annual precipitation moves through soil to recharge groundwater and leaches 11 to 18 kg ha -1 yr -1 of nitrate-N from soil. These leaching rates are approximately 20-30% of fertilizer rates but likely reflect inmixing of nitrate from SON decomposition. Soil modeling analyses suggested that water and N losses were dominated by intense precipitation periods on wetter soils, such that more than half of simulated deep percolation and leaching occurred in two of 14 model years. Simulations further suggest that thinner soils (<25 cm fine-textured materials) experience water and nitrate loss rates five to 16 times higher than thicker soils (>100 cm). Soil sampling demonstrated that increased soil water during fallow periods facilitates conversion of SON to nitrate. Soils are then primed for water and N loss with subsequent precipitation, resulting in disproportionately high leaching rates during and following fallow periods. Isotopic evidence from fallow periods further suggests that nitrate is lost to the atmosphere via denitrification, a gas phase loss combining with leaching losses to compromise the goal of delivering N to crops. These findings suggest that reduction of fallow increases N use efficiency and reduces nitrate loss to groundwater.Item Evaluation of nitorgen and carbon supplementation strategies for optimizing biomass generation during cultivation of Chlorella sorokiniana, strain SLA-04(Montana State University - Bozeman, College of Engineering, 2021) Jackson, Matthew Clifford; Chairperson, Graduate Committee: Catherine KirklandAlgal cultivation requires significant nitrogen and carbon inputs, which are expensive and can offset benefits associated with biofuel production. This research investigates growth of an alkali-tolerant Chlorella sorokiniana, strain SLA-04, using different nitrogen and carbon regimes to improve physiological knowledge of this novel organism, and improve biomass production and resource demand. Nitrate, ammonium, and urea were used efficiently by SLA-04, however pH changes during utilization of nitrate and ammonium impacted inorganic carbon availability (species and concentration). Generation of OH- during use of nitrate increased pH, increasing mass transfer of CO 2 into solution and increasing the ratio of HCO 3-/CO 2. Ammonium utilization resulted in proton generation, lowering pH and inhibiting growth. When bicarbonate, rather than CO 2, was provided, productivity improved for the urea and mixed nitrogen conditions. This likely resulted from upregulation of genes related to nitrogen and carbon assimilation in the presence of bicarbonate, however Na + cotransport with urea and nitrate is required in some organisms. It is possible that Na + was insufficient when CO 2 was provided, but not in conditions with bicarbonate since it was added as NaHCO 3-. The impact of Na +, as well as other ions, on nitrogen and carbon utilization is not well understood, but it may alter gene regulation. Bicarbonate and CO 2 both promoted increased growth relative to cultures without inorganic carbon supplementation. The highest productivities were observed when carbon supplementation, either as continued CO 2 augmentation to the air sparge or as a 50mM bicarbonate amendment, was provided during nitrogen deplete growth. Glucose availability improved productivity for conditions without CO 2 supplementation. The use of urea or a combination of nitrogen sources with bicarbonate, instead of CO 2, was promising due to (a) the low cost of urea, relative to the other nitrogen sources; (b) the potential for using wastewater containing a mix of nitrogen sources; and (c) the low cost and easy transport of bicarbonate. Future research should evaluate changes in SLA-04 gene expression resulting from the supply of different nutrients, including nitrogen and carbon sources, as well as other ions essential for growth.Item Impacts of crop rotations and nitrogen fertilizer on soil biological factors in semi-arid Montana(Montana State University - Bozeman, College of Agriculture, 2021) Fouts, Willa Constance; Chairperson, Graduate Committee: Catherine A. ZabinskiEvaluating the effects of cropping and fertilizing techniques is key to informing agricultural best practices. We must continue monitoring how we manipulate soils in order to preserve and cultivate high-quality soil ecosystems that can support us in the face of climate change and widespread soil loss and deterioration. We assessed the effects of common agricultural practices in Montana by measuring biological indicators of soil quality in the 18th year of a field plot experiment with 100% and 50% the recommended rate of synthetic nitrogen (N) fertilizer and crop rotations incorporating wheat, fallow, and legumes. The biological indicators measured were four soil extracellular enzymes, potentially mineralizable N (PMN), and microbial biomass. We sampled once in spring 2020 and subsampled in the fall. We also tested whether enzymes and PMN were correlated to aboveground plant residue, which was represented by the sum of the dried plant mass from past two years left on the plots after harvest. Plant residue was positively correlated with the C, N, and S-cycling enzymes and to PMN. The positive correlation between PMN and residue reflects that increased biomass inputs could increase easily mineralizable N. Soil with the high N-rate had a slightly higher geometric mean enzyme activity. This could be from the resulting increase in plant residue. The high N-rate treatment slightly decreased soil PMN but was not affected by crop rotation treatments. Fallow systems had lower enzyme function overall, indicating a lessened fertility and decomposition rate compared to continuously cropped treatments, which keep the soil covered with a crop for more months out of the year. The positive correlations of plant residue, along with the general lower performance of the fallow systems, especially the tilled fallow rotation, support that aboveground biomass inputs are a driver in soil ecosystem function. Continuous no-till crop rotations have increased aboveground plant organic matter, which could increase nutrient cycling and decomposition, and thereby soil biological quality and fertility.Item Pest management challenges and climate change in water limited winter wheat agroecosystems in southwestern Montana(Montana State University - Bozeman, College of Agriculture, 2020) Nixon, Madison Grace; Chairperson, Graduate Committee: Fabian D. MenalledDryland winter wheat production is influenced by many environmental factors including climate, disease, and resource availability. In Montana, Bromus tectorum (cheatgrass) and Fusarium pseudograminearum (a fungus causing root crown rot) are major winter wheat pests; reducing yield and grain quality. However, little is known how climate change and resource availability impact winter wheat, B. tectorum, and F. pseudograminearum individually as well as their multi-trophic interactions. Thus, this research aimed to 1) Determine the susceptibility of B. tectorum to F. pseudograminearum and assess how CO 2 and nitrogen impact their growth, and 2) Evaluate how elevated temperature, reduced precipitation, and plant competition impact winter wheat and B. tectorum growth and reproduction. Utilizing growth chambers, high and low nitrogen treatments, fungal inoculated and uninoculated treatments, and ambient and elevated CO 2 treatments, Bromus tectorum was found to be a host of F. pseudograminearum, and the fungus significantly reduced root, shoot and total biomass, as well as primary physiological processes of B. tectorum. Fusarium pseudograminearum infection was not impacted by nitrogen or CO 2 level. Low nitrogen increased emergence and root production early on, while high nitrogen increased shoot production at later growth stages. Low nitrogen also improved stomatal conductance and transpiration rate. High CO 2 increased B. tectorum root, shoot, and biomass production, as well as intercellular CO 2. An interaction between ambient CO 2 and low nitrogen resulted in the greatest shoot relative growth rate between the first and second harvest. Field tests, using three climate treatments (ambient, increased temperature, reduced precipitation with increased temperature) and three plant competition levels (monoculture winter wheat, monoculture B. tectorum, and biculture of the two), found that for both winter wheat and B. tectorum monocultures, ambient and warmer climates produced similar yields and biomass, respectively, whereas the drier with warmer treatment reduced these factors. Additionally, B. tectorum presence increased winter wheat grain protein. A quadratic interaction model of winter wheat yield as a function of B. tectorum biomass by climate treatment suggests that at low to moderate B. tectorum biomass levels, winter wheat yield was negatively impacted by the warmer and drier treatment, whereas ambient and warmer treatment results were similar.Item Linking plant and soil nutrient dynamics in temperate and tropical montane forests(Montana State University - Bozeman, College of Letters & Science, 2018) Qubain, Claire Anne; Chairperson, Graduate Committee: David Roberts; Jia Hu (co-chair); Yuriko Yano and Jia Hu were co-authors of the article, 'Linking nitrogen allocation in douglas-fir to soil nitrogen availability in a western montane conifer forest' submitted to the journal 'Oecologia' which is contained within this thesis.; Diego Riveros-Iregui and Jia Hu were co-authors of the article, 'Climate and invasion drive soil nutrient dynamics in tropical montane forests of the Galapagos archipelago' submitted to the journal 'Ecology' which is contained within this thesis.I built on our fundamental understanding of ecosystem function by examining how climate variability influences feedbacks between plant processes and soil nutrient dynamics. At Lubrecht Experimental Forest, I examined how variability in snow depth, precipitation, and soil moisture influenced seasonal nitrogen allocation in Douglas-fir. I then examined if N cycling within Douglas-fir synchronized with patterns of N availability in the soil. In this case, N availability in the soil influenced plant nutrient dynamics. On the other hand, on San Cristobal Island in the Galapagos Archipelago, plants fed back and influenced soil nutrient dynamics. Changes in precipitation, soil moisture, and temperature strongly controlled nutrient concentrations in the soil, and to a lesser degree, plant community type determined nutrient concentrations, especially N concentrations, in the soil.Item Impact of nitrogen and water management to grain yield, yield components and traits, and grain quality of two contrasting wheat classes(Montana State University - Bozeman, College of Letters & Science, 2019) Bicego Vieitez de Almeida, Breno; Chairperson, Graduate Committee: Luther E. Talbert and Jessica Torrion (co-chair); Anish Sapkota and Jessica A. Torrion were co-authors of the article, 'Differential nitrogen and water impacts on yield and quality of wheat classes' which is contained within this thesis.; Jessica A. Torrion was a co-author of the article, 'Nitrogen and water impacts on grain yield and components of different wheat classes' which is contained within this thesis.Wheat (Triticum aestivum L.) breeders and physiologists must consider not only grain yield but also its quality. Physiological selection may be an important tool to aid breeders achieve improvements more rapidly. However, different genotypes may have distinct responses to agronomic management and environments. The relationship between those traits also may vary according to wheat class. In the present study we characterized the grain yield, yield components and traits, and quality parameters response of four hard red and four soft white spring wheat cultivars subjected to various nitrogen (N) levels and moisture regimes (stressed vs non-stressed environment) over two years. About one-third grain yield reduction from 2016 to 2017 could be attributed to heat stress. Overall, soft whites had higher grain yield than hard reds, but a stronger negative grain yield-grain protein content relationship. Considering a given year, increments in grain yield also resulted in higher grain protein in hard reds except when N was very low. The cultivar with Gpc-B1 gene for higher grain protein, had similar grain yield to its parent material and to other well adapted hard red cultivar. Vida, characterized by extended green leaf duration after heading (stay-green trait), was better adapted to water and heat stress than the rest of hard reds. Grain fill duration was an important trait especially under heat and drought stress for both wheat classes. We found that, across moisture regime environments and year, productive tiller number had consistently a direct relation with kernel number per area, which was strongly related to grain yield. During the heat and drought stressed year, kernel weight was an important yield component and had neutral relation with kernel number. Nitrogen fertilization had effect on grain yield only during the hot and dry year with irrigation, but no effect was observed under rainfed conditions for this year. Based on the lower grain protein requirement as well the lack of N effect on grain yield for the tested conditions, soft whites may be grown with lower N input than hard reds.