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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Nitrogen-Fixing Gamma Proteobacteria Azotobacter vinelandii—A Blueprint for Nitrogen-Fixing Plants?

The availability of fixed nitrogen limits overall agricultural crop production worldwide. The so-called modern “green revolution” catalyzed by the widespread application of nitrogenous fertilizer has propelled global population growth. It has led to imbalances in global biogeochemical nitrogen cycling, resulting in a “nitrogen problem” that is growing at a similar trajectory to the “carbon problem”. As a result of the increasing imbalances in nitrogen cycling and additional environmental problems such as soil acidification, there is renewed and increasing interest in increasing the contributions of biological nitrogen fixation to reduce the inputs of nitrogenous fertilizers in agriculture. Interestingly, biological nitrogen fixation, or life’s ability to convert atmospheric dinitrogen to ammonia, is restricted to microbial life and not associated with any known eukaryotes. It is not clear why plants never evolved the ability to fix nitrogen and rather form associations with nitrogen-fixing microorganisms. Perhaps it is because of the large energy demand of the process, the oxygen sensitivity of the enzymatic apparatus, or simply failure to encounter the appropriate selective pressure. Whatever the reason, it is clear that this ability of crop plants, especially cereals, would transform modern agriculture once again. Successfully engineering plants will require creating an oxygen-free niche that can supply ample energy in a tightly regulated manner to minimize energy waste and ensure the ammonia produced is assimilated. Nitrogen-fixing aerobic bacteria can perhaps provide a blueprint for engineering nitrogen-fixing plants. This short review discusses the key features of robust nitrogen fixation in the model nitrogen-fixing aerobe, gamma proteobacteria Azotobacter vinelandii, in the context of the basic requirements for engineering nitrogen-fixing plants.

Microbiology↗
DOE OSTI2026

How nitrogen and oxygen shape SRF cavity performance

Nitrogen and oxygen-based surface treatments have revolutionized the performance of superconducting radiofrequency (SRF) cavities, enabling them to reach higher gradients and lower losses. However, the exact mechanisms by which these treatments improve cavity performance remain largely unknown. This work provides new insights into the role of nitrogen and oxygen in SRF cavity performance by using time-of-flight secondary ion mass spectrometry (TOF-SIMS) to precisely quantify the concentrations and depth profiles of these impurities within niobium cutouts. We correlate these impurity profiles with detailed cavity performance measurements, including surface resistance and quality factor, and compare our findings with predictions from BCS theory. The results demonstrate that while both nitrogen and oxygen enhance performance, ten times more oxygen is required to achieve the same reduction in BCS resistance as interstitial nitrogen. We present a potential model in which the observed variation arises from nitrogen's greater effectiveness in trapping hydrogen, thus reducing the formation of niobium hydrides and enhancing superconducting gap.

Hu, Hannah [Chicago U.]↗
DOE OSTI2024

Insights into Sustainable Nitrogen Fixation by Gas-phase Spectroscopic Measurements and Global Modeling of Reaction Intermediates in Humid Nitrogen Plasma

In this article, there is growing interest in reacting molecular nitrogen and water to sustainably synthesize fixed forms of nitrogen such as ammonia. In particular, low-temperature plasmas can activate these relatively inert feedstocks at or near room temperature without a catalyst. However, because of the enhanced reactivity and nonequilibrium chemistry, a diverse range of products is formed, and the underlying reaction mechanisms are exceedingly complex. In this work, we studied a simplified reactor consisting of a gaseous plasma containing controlled mixtures of nitrogen gas and water vapor. Densities of key chemical species such as N, H, OH, NH, and NO were measured by emission and laser-based spectroscopy as a function of the relative humidity. A global model was constructed and the reaction network was validated by comparing calculated species densities with experiments. We discover that N, a key initial intermediate for ammonia, strongly decreases in the presence of water vapor, and as a result, ammonia formation becomes limited at high relative humidity. This decrease is surprisingly not because N itself reacts, but because one of its main sources, an excited molecular nitrogen state, is reacted away. In addition, oxidation pathways for nitrogen, which lead to NO and related products, are found to be favored over reduction pathways because the corresponding reverse reactions are less significant. Together, this understanding helps explain previously reported observations of selectivity toward nitrogen oxides over ammonia, particularly at higher relative humidities.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Data for Nitrogen Dynamics and Physiological N Use Efficiency in High-biomass Sorghum

Improving nitrogen (N) efficiency is essential for sustainable high-biomass sorghum ( Sorghum bicolor L. Moench ) production. This study evaluated leaf and stem N dynamics, canopy N remobilization, and physiological nitrogen use efficiency (pNUE) in two photoperiod-sensitive sorghum hybrids under two N rates (0 and 168 kg-N ha−1) across multiple environments in Texas and Illinois. Leaf N concentrations increased with plant height in the canopy with steeper gradients under low-N conditions, indicating enhanced N remobilization when N is limited. Stem tissue showed less variation in N concentration across canopy nodal positions, with within-plant differences ranging from 1.2 to 7.6 g kg−1, compared to 3.1 to 16.3 g kg−1 in leaves. While pNUE was generally higher under unfertilized conditions, it varied largely by site; however, genotypic differences were minimal within the given year. These results highlight the importance of integrating environmental and management factors into breeding and fertilization strategies to enhance N efficiency in high-biomass sorghum.

Nitrogen↗
DOE OSTI2024

Decoupling of Nitrogen and Oxygen Impurities in Nitrogen Doped SRF Cavities

The performance of superconducting radiofrequency (SRF) cavities is critical to enabling the next generation of efficient high-energy particle accelerators. Recent developments have focused on altering the surface impurity profile through \textit{in-situ} baking, furnace baking, and doping to introduce and diffuse beneficial impurities such as nitrogen, oxygen, and carbon. However, the precise role and properties of each impurity are not well understood. In this work, we attempt to disentangle the role of nitrogen and oxygen impurities through time-of-flight secondary ion mass spectrometry of niobium samples baked at temperatures varying from 75-800 $^\circ$C with and without nitrogen injection. From these results, we developed treatments recipe that decouple the effects of oxygen and nitrogen in doping treatments. Understanding how these impurities and their underlying mechanisms drive further optimization in the tailoring of impurity profiles for high-performance SRF cavities.

43 PARTICLE ACCELERATORS↗
DOE OSTI2024

Decoupling of Nitrogen and Oxygen Impurities in Nitrogen Doped SRF Cavities

The performance of superconducting radiofrequency (SRF) cavities is critical for enabling the next generation of efficient high-energy particle accelerators. Recent developments have focused on altering the surface impurity profile through \textit{in-situ} baking, furnace baking, and doping to introduce and diffuse beneficial impurities such as nitrogen, oxygen, and carbon. However, the precise role and properties of each impurity are not well understood. In this work, we attempt to disentangle the role of nitrogen and oxygen impurities through time-of-flight secondary ion mass spectrometry using niobium cavity cutouts baked at temperatures varying from 120-800$^\circ$C with and without nitrogen injection. Understanding the underlying mechanisms behind these impurities will drive further optimization in the tailoring of nitrogen and oxygen profiles for high-performance SRF cavities.

43 PARTICLE ACCELERATORS↗
DOE OSTI2026

Data for Impacts of Legacy and Contemporary Nitrogen Inputs on N2O and CO2 Emissions in Miscanthus and Maize Cultivated Soils

Nutrient inputs influence the sustainability of bioenergy crop production through contemporary (shortly after addition) and legacy effects (persisting over years) on microbial nitrogen (N) and carbon cycling, which contribute to greenhouse gas emissions. However, the relative importance of contemporary and legacy effects and how that could vary by crop functional types is poorly understood. Considering its rhizomatous roots and perennial growth, we hypothesized that Miscanthus × giganteu s ( M × g ) would be more sensitive to legacy N fertilization and the historical context of its environment than an annual crop like maize. To test this hypothesis, we examined the effects of legacy and contemporary N inputs on nitrous oxide (N2O) and carbon dioxide (CO2) emissions, as well as key N cycling genes in soils where M × g and maize were grown. A 150-day soil incubation experiment was conducted using soils from a long-term M × g and maize fertility experiment with three historic N fertilization rates (0, 112, and 336 kg N ha−1 year−1) and a contemporary amendment (60 mg N kg−1) with negative control (0 mg N kg−1). We observed significant increases in cumulative N2O emissions in M × g soils relative to maize soils, particularly at higher legacy fertilization rates, while contemporary N had no significant effect. Bacterial amoA gene abundance, which plays a significant role in nitrification in nutrient-rich soils, also increased with higher legacy fertilization rates in M × g soils but was unaffected by the contemporary N. In maize soils, legacy and contemporary N did not significantly affect N2O emissions, but cumulative CO2 emissions and amoA gene abundance significantly increased. The abundances of norB genes were not significantly influenced by either legacy fertilization or contemporary N amendments in either soil. Our findings demonstrate the greater importance of fertilization history over contemporary N in mediating soil N2O emissions, particularly for perennial bioenergy crops.

Carbon↗
DOE OSTI2026

Function, Structure, and Regulation of Nitrogen Fixation-like Metalloproteins for Nitrogen, Energy, Carbon, and Sulfur Metabolism

Nitrogenases (N 2 ases) and nitrogen fixation-like (NFL) systems play distinct roles in nitrogen, carbon, sulfur, and energy metabolism based on their fundamental differences in structure and metallocofactor identity. As new NFL systems have recently been identified and characterized, striking parallels and differences compared to N 2 ase structure, catalysis, and regulation have emerged. NFL systems use metallocofactors that span from simple [4Fe-4S] clusters to complex clusters akin to FeMo-co, previously only thought to occur in N 2 ase. This review describes the present state of knowledge on the function, structure, catalytic mechanisms, and regulation of NFL systems that perform distinct biological roles across all three domains of life. Recent advancements in N 2 ase spectroscopic techniques for probing metallocofactor structure and electronic states guide current and future work on how each NFL system catalyzes its specific biological reaction(s). Key knowledge gaps and needed areas of research for uncovering the specific metallocofactors and structural motifs that are at the heart of NFL system reaction specificity, along with how these systems are regulated, are discussed.

Bacteria↗
DOE OSTI2024

Mycorrhizal associations of temperate forest seedlings mediate rhizodeposition, but not soil carbon storage, under elevated nitrogen availability

Abstract Tree‐mycorrhizal associations are associated with patterns in nitrogen (N) availability and soil organic matter storage; however, we still lack a mechanistic understanding of what tree and fungal traits drive these patterns and how they will respond to global changes in soil N availability. To address this knowledge gap, we investigated how arbuscular mycorrhizal (AM)‐ and ectomycorrhizal (EcM)‐associated seedlings alter rhizodeposition in response to increased seedling inorganic N acquisition. We grew four species each of EcM and AM seedlings from forests of the eastern United States in a continuously 13 C‐labeled atmosphere within an environmentally controlled chamber and subjected to three levels of 15 N‐labeled fertilizer. We traced seedling 15 N uptake from, and 13 C‐labeled inputs (net rhizodeposition) into, root‐excluded or ‐included soil over a 5‐month growing season. N uptake by seedlings was positively related to rhizodeposition for EcM‐ but not AM‐associated seedlings in root‐included soils. Despite this contrast in rhizodeposition, there was no difference in soil C storage between mycorrhizal types over the course of the experiment. Instead root‐inclusive soils lost C, while root‐exclusive soils gained C. Our findings suggest that mycorrhizal associations mediate tree belowground C investment in response to inorganic N availability, but these differences do not affect C storage. Continued soil warming and N deposition under global change will increase soil inorganic N availability and our seedling results indicate this could lead to greater belowground C investment by EcM‐associated trees. This potential for less efficient N uptake by EcM‐trees could contribute to AM‐tree success and a shift toward more AM‐dominated temperate forests.

Fitch, Amelia A.↗
DOE OSTI2024

Decarbonizing nitrogen fertilizer production via the electrochemical nitrogen oxidation reaction

Nitric acid is an important commodity chemical with extensive applications in both agricultural and industrial sectors. However, current production methods involve a combination of the Haber–Bosch and Ostwald processes, which are both energy and carbon emission intensive. The electrochemical nitrogen oxidation reaction (NOR) to produce nitric acid or nitrates shows great potential as an environmentally friendly method for producing fertilizers under mild conditions. The key to progress in this field lies in understanding the fundamental mechanistic insights and establishing robust experimental methods, which is essential for the efficient design and synthesis of electrocatalysts for NOR. Additionally, poor gas mass transport in conventional electrochemical reactors at present lead to lower NOR activity, thereby limiting the progress in this field. In this work, we present a synergistic computational and experimental approach to map out the potential chemical and electrochemical steps and determine the energetics on PtO 2 catalyst to gain mechanistic insights into NOR. Here, this study marks the first attempt to perform NOR in a vapor-fed reactor designed using advanced (additive) manufacturing. The vapor-fed reactor significantly improved the N 2 mass transport to the catalyst, allowing us to report the highest rate for nitrate production to date at 3.3 μmol cm -2 h -1 at 2.01 V vs RHE.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2025

Carbon availability, soil pH, and microbial allocation to nitrogen acquisition shape grassland heterotrophic respiration in response to a decade of nitrogen addition

Previous work has found that anthropogenic inputs of nitrogen (N) and phosphorus (P) impact heterotrophic respiration during soil organic matter decomposition in grasslands, a critical pathway through which carbon (C) is lost from soil to the atmosphere. While N addition typically reduces heterotrophic respiration, why the strength and direction of this N effect varies among sites is unclear. Here, to address this, we conducted a 339-day laboratory incubation to measure heterotrophic respiration from nine grasslands across North America that have received 10 years of factorial N and P fertilization. N addition reduced cumulative respiration most at sites with low pH, low microbial allocation towards N acquisition, and high soil C concentration and availability. However, N addition had neutral rather than positive effects on heterotrophic respiration in sites with high pH and decomposer allocation towards N acquisition. Across sites, a decade of N addition reduced heterotrophic respiration by ∼24 %, driven by reductions in microbial biomass. Heterotrophic respiration was less sensitive to P addition, despite its increasing microbial biomass. However, simultaneous N and P addition did ameliorate negative N effects. These results show that previously observed variation in the response of heterotrophic respiration to N addition can be explained by soil C availability and pH status, widely measured factors which can be used to predict how grassland C fluxes may change under continuing nutrient deposition.

N addition↗
DOE OSTI2024

Nitrogen Deposition Weakens Soil Carbon Control of Nitrogen Dynamics Across the Contiguous United States

ABSTRACT Anthropogenic nitrogen (N) deposition is unequally distributed across space and time, with inputs to terrestrial ecosystems impacted by industry regulations and variations in human activity. Soil carbon (C) content normally controls the fraction of mineralized N that is nitrified ( ƒ nitrified ), affecting N bioavailability for plants and microbes. However, it is unknown whether N deposition has modified the relationships among soil C, net N mineralization, and net nitrification. To test whether N deposition alters the relationship between soil C and net N transformations, we collected soils from coniferous and deciduous forests, grasslands, and residential yards in 14 regions across the contiguous United States that vary in N deposition rates. We quantified rates of net nitrification and N mineralization, soil chemistry (soil C, N, and pH), and microbial biomass and function (as beta‐glucosidase (BG) and N ‐acetylglucosaminidase (NAG) activity) across these regions. Following expectations, soil C was a driver of ƒ nitrified across regions, whereby increasing soil C resulted in a decline in net nitrification and ƒ nitrified . The ƒ nitrified value increased with lower microbial enzymatic investment in N acquisition (increasing BG:NAG ratio) and lower active microbial biomass, providing some evidence that heterotrophic microbial N demand controls the ammonium pool for nitrifiers. However, higher total N deposition increased ƒ nitrified , including for high soil C sites predicted to have low ƒ nitrified , which decreased the role of soil C as a predictor of ƒ nitrified . Notably, the drop in contemporary atmospheric N deposition rates during the 2020 COVID‐19 pandemic did not weaken the effect of N deposition on relationships between soil C and ƒ nitrified . Our results suggest that N deposition can disrupt the relationship between soil C and net N transformations, with this change potentially explained by weaker microbial competition for N. Therefore, past N inputs and soil C should be used together to predict N dynamics across terrestrial ecosystems.

Nieland, Matthew A. [Stockbridge School of Agricul↗
DOE OSTI2024

Nitrogen‐Nitrogen Bond Breaking in Irradiation Products of Hexanitrohexaazaisowurtzitane (CL‐20)

While the primary result of an interaction of ionizing radiation with an organic material is the ejection of electrons from molecular orbitals producing cations, the free electrons can further interact, yielding excited states; and, potentially, anions. In this work, we computed reaction barriers and energies for N−N bond breaking in the CL-20 cation, anion, and excited state to investigate if CL-20 degradation is accelerated after radiation exposure. We focused on N−N bond dissociation because it is the rate-determining step in the thermal degradation of CL-20. We found that N−N cleavage rapidly takes place in the CL-20 cation and anion with greatly reduced reaction energies as compared to CL-20. We also outlined a potential path for photodissociation of the N−N bond. While CL-20 is kinetically stable, initial degradation occurs readily in its irradiation products. In conclusion, this is of importance for the performance of the explosive after high-dose exposure and influences aging if CL-20 is irradiated at a low dose over extended periods of time.

CL-20 anion↗