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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Quantitative DNA Stable Isotope Probing Identifies Active Microorganisms Assimilating Volatile Fatty Acids in Full-Scale Enhanced Biological Phosphorus Removal Processes

Enhanced biological phosphorus removal (EBPR) systems often rely on exogenous carbon sources, such as volatile fatty acids (VFAs), to achieve higher P removal. Here, we employed DNA quantitative stable isotope probing (qSIP) using two VFAs, acetate and propionate, in cyclic anaerobic/aerobic incubations to assess their effects on P cycling and microbial activity with biomass from two full-scale EBPR water resource-recovery facilities that utilize VFA addition. We found that anaerobic VFA uptake preferences differed within known groups of PAOs, such as Candidatus Accumulibacter and Tetrasphaera-affiliated members (e.g., Ca. Phosphoribacter), between the two biomasses. The combination of qSIP with metagenomics identified isotopically labeled phages that were linked to active PAOs, highlighting their potential roles in modulating EBPR community composition and activity. The highest levels of anaerobic labeling from acetate were in genomes belonging to Saccharimonadales and Rickettsiales, which are generally host-associated with bacteria and eukaryotes, respectively. Furthermore, this finding highlights the possibility of cross-feeding between PAO hosts and their parasites or predators, as well as the role of so-far uncharacterized organisms participating in carbon cycling under EBPR conditions. Collectively, these results expand our understanding of the ecological interactions involved in communities anaerobically uptaking VFAs and cycling P that are central to EBPR.

Polyphosphate accumulating organisms↗
DOE OSTI2024

Skeletal Kinetics Reduction for Astrophysical Reaction Networks

A novel methodology is developed to extract accurate skeletal reaction models for nuclear combustion. Local sensitivities of isotope mass fractions with respect to reaction rates are modeled based on the forced optimally time-dependent (f-OTD) scheme. These sensitivities are then analyzed temporally to generate skeletal models. The methodology is demonstrated by conducting skeletal reduction of constant density and temperature burning of carbon and oxygen relevant to Type Ia supernovae (SNe Ia). The 495-isotopes Torch model is chosen as the detailed reaction network. A map of maximum production of 56 Ni in SNe Ia is produced for different temperatures, densities, and proton-to-neutron ratios. The f-OTD simulations and the sensitivity analyses are then performed with initial conditions from this map. A series of skeletal models are derived and their performances are assessed by comparison against currently existing skeletal models. Previous models have been constructed intuitively by assuming the dominance of α-chain reactions. The comparison of the newly generated skeletal models against previous models is based on the predicted energy release and 44 Ti and 56 Ni abundances by each model. The consequences of ye ≠ 0.5 in the initial composition are also explored where ye is the electron fraction. The simulated results show that 56 Ni production decreases by decreasing ye as expected, and that the 43 Sc is a key isotope in proton and neutron channels toward 56 Ni production. It is shown that an f-OTD skeletal model with 150 isotopes can accurately predict the 56Ni abundance in SNe Ia for ye ≲ 0.5 initial conditions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Understanding long-term groundwater flow at Pahute Mesa and vicinity, Nevada National Security Site, USA, from naturally occurring geochemical and isotopic tracers

Abstract Recently collected naturally occurring geochemical and isotopic groundwater tracers were combined with historic data from the Pahute Mesa area of the Nevada National Security Site (NNSS), Nevada, USA, to provide insights into long-term regional groundwater flow patterns, mixing and recharge. Pahute Mesa was the site of 85 nuclear detonations between 1965 and 1992, many of them deeply buried devices that introduced radionuclides directly into groundwater. The dataset examined included major ions and field measurements, stable isotopes of hydrogen (δ 2 H), oxygen (δ 18 O), carbon (δ 13 C) and sulfur (δ 34 S), and radioisotopes of carbon ( 14 C) and chloride ( 36 Cl). Analysis of the patterns of groundwater 14 C data and the δ 2 H and δ 18 O signatures indicates that groundwater recharge is predominantly of Pleistocene age, except for a few localized areas near major ephemeral drainages. Steep gradients in sulfate (SO 4 ) and chloride (Cl) define a region near the western edge of the NNSS where high-concentration groundwater flowing south from north of the NNSS merges with dilute groundwater flowing west from eastern Pahute Mesa in a mixing zone that coincides with a groundwater trough associated with major faults. The 36 Cl/Cl and δ 34 S data suggest that the source of the high Cl and SO 4 in the groundwater was a now-dry, pluvial-age playa lake north of the NNSS. Patterns of groundwater flow indicated by the combined data sets show that groundwater is flowing around the northwest margin of the now extinct Timber Mountain Caldera Complex toward regional discharge areas in Oasis Valley.

58 GEOSCIENCES↗
DOE OSTI2021

Competitive Exclusion and Metabolic Dependency among Microorganisms Structure the Cellulose Economy of an Agricultural Soil

Microorganisms that degrade cellulose utilize extracellular reactions that yield free by-products which can promote interactions with noncellulolytic organisms. We hypothesized that these interactions determine the ecological and physiological traits governing the fate of cellulosic carbon (C) in soil. We performed comparative genomics with genome bins from a shotgun metagenomic-stable isotope probing experiment to characterize the attributes of cellulolytic and noncellulolytic taxa accessing 13 C from cellulose. We hypothesized that cellulolytic taxa would exhibit competitive traits that limit access, while noncellulolytic taxa would display greater metabolic dependency, such as signatures of adaptive gene loss. We tested our hypotheses by evaluating genomic traits indicative of competitive exclusion or metabolic dependency, such as antibiotic production, growth rate, surface attachment, biomass degrading potential, and auxotrophy. The most 13 C-enriched taxa were cellulolytic Cellvibrio (Gammaproteobacteria) and Chaetomium (Ascomycota), which exhibited a strategy of self-sufficiency (prototrophy), rapid growth, and competitive exclusion via antibiotic production. Auxotrophy was more prevalent in cellulolytic Actinobacteria than in cellulolytic Proteobacteria, demonstrating differences in dependency among cellulose degraders. Noncellulolytic taxa that accessed 13 C from cellulose (Planctomycetales, Verrucomicrobia, and Vampirovibrionales) were also more dependent, as indicated by patterns of auxotrophy and 13 C labeling (i.e., partial labeling or labeling at later stages). Major 13 C-labeled cellulolytic microbes (e.g., Sorangium, Actinomycetales, Rhizobiales, and Caulobacteraceae) possessed adaptations for surface colonization (e.g., gliding motility, hyphae, attachment structures) signifying the importance of surface ecology in decomposing particulate organic matter. Our results demonstrated that access to cellulosic C was accompanied by ecological trade-offs characterized by differing degrees of metabolic dependency and competitive exclusion.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Coupled feldspar dissolution and secondary mineral precipitation in batch systems: 6. Labradorite dissolution, calcite growth, and clay precipitation at 60 °C and pH 8.2–8.4

Here, we conducted experiments on concurrent labradorite dissolution, calcite precipitation, and clay precipitation in batch reactor systems and tracked reaction processes using multiple isotope tracers. Labradorite was chosen for its role as a major and reactive component in basalt; the experiments thus directly impact our understanding of CO 2 storage in basalt aquifers and enhanced rock weathering. We doped initial solutions with 29 Si, 43 Ca, and Ca 13 CO 3 (s). Experiments were conducted at 60 °C and pH ~ 8.3 for up to 840 h, with isotope ratios in the experimental aqueous solutions measured using MC-ICP-MS. Unidirectional rates of labradorite dissolution near equilibrium were approximately two orders of magnitude slower than far-from-equilibrium rates reported in the literature. Calcite growth occurred near equilibrium and the rates were limited by the labradorite dissolution rates. In the steady state phase, the interplay of these three heterogeneous reactions—labradorite dissolution, calcite growth, and clay precipitation—results in a coupled system that approaches a near-equilibrium state. The system does not reach true equilibrium because labradorite continues to dissolve, albeit at a much slower rate near equilibrium. The overall reaction can be approximated as, Na 0.4 Ca 0.6 Al 1.6 Si 2.4 O 8 + 0.6HCO 3 - + 1·.7H 2 O + 0.4H + → 0.4Na + + 0.6CaCO 3(s) + 0.5Al 2 Si 2 O 5 (OH) 4(s) + 0.6Al(OH) 4 - + 1.4SiO 2 o (aq). The experimental results show that using short-term far-from-equilibrium rate constants would lead to an overestimation of feldspar weathering rates at the Earth’s surface (e.g., basalt weathering and enhanced rock weathering) and CO 2 mineralization in basalt aquifers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Tarda and Tagish Lake: Samples from the same outer Solar System asteroid and implications for D- and P-type asteroids

Here, we report a comprehensive study of the ungrouped type 2 carbonaceous chondrite, Tarda, which fell in Morocco in 2020. This meteorite exhibits substantial similarities to Tagish Lake, Wisconsin Range 91600, and Meteorite Hills 00432, which are generally considered to have originated from a D-type asteroid(s). We constrain the compositions and petrologies of the materials present in a potential sample of a D-type asteroid by reporting the petrography, bulk chemical compositions, bulk H, C, N, Cr, and Ti isotopic compositions, reflectance spectra, and in situ chemical compositions of metals, sulfides, carbonates, and FeO-poor and FeO-rich chondrule silicates of Tarda. We also present new data for Tagish Lake. We then compare Tarda with the other Tagish Lake-like meteorites. Tarda and Tagish Lake appear to be from the same parent body, as demonstrated by their similar petrologies (modal abundances, chondrule sizes), mineral compositions, bulk chemical and isotopic compositions, and reflectance spectra. While the two other Tagish Lake-like meteorites, Wisconsin Range 91600 and Meteorite Hills 00432, show some affinities to Tagish Lake and Tarda, they also share similar characteristics to the Mighei-like carbonaceous (CM) chondrites, warranting further study. Similarities in reflectance spectra suggest that P-type asteroids 65 Cybele and 76 Freia are potential parent bodies of Tarda and the Tagish Lake-like meteorites, or at least have similar surface materials. Since upcoming spacecraft missions will spectrally survey D-type, P-type, and C-type Trojan asteroids (NASA's Lucy) and spectrally study and return samples from Mars' moon Phobos (JAXA's Martian Moons eXploration mission), which is spectrally similar to D-type asteroids, these meteorites are of substantial scientific interest. Furthermore, since Tarda closely spectrally matches P-type asteroids (but compositionally matches the D-type asteroid like Tagish Lake meteorite), P-type and D-type asteroids may represent fragments of the same or similar parent bodies.

58 GEOSCIENCES↗
DOE OSTI2026

Role of Surface Hydroxyls and Lattice Oxygen in Governing Selectivity and Restructuring During Acetic Acid Conversion on Fe 3 O 4 (001)

Understanding the reactivity of carboxylic acids on metal oxide surfaces is critical for elucidating ketonization mechanisms relevant to biomass upgrading. Here, we investigate the adsorption and thermal decomposition of acetic acid (CH 3 COOH) on Fe 3 O 4 (001) using scanning tunneling microscopy (STM), temperature-programmed reaction spectroscopy (TPRS), and X-ray photoelectron spectroscopy (XPS). At room temperature, acetic acid adsorbs dissociatively to form ordered bidentate acetate (CH 3 COO) overlayer that lifts the (√2 × √2)R 45° surface reconstruction. TPRS reveals ketene (CH 2 CO) as the dominant product, along with CO, CO 2 , and H 2 O, the latter evolving via a Mars–van Krevelen (MvK) mechanism. Isotopic labeling shows preferential CO 2 formation from the carboxyl carbon and a more balanced CO/CO 2 ratio from the methyl carbon, suggesting distinct oxidation pathways. STM imaging reveals embedded acetate intermediates filling surface oxygen vacancies created in MvK steps. Upon product formation completion (~700 K), extensive surface etching is observed, with pits elongated along the octahedral Fe rows. Approximately 20% of the surface oxygen is removed, consistent with vacancy formation stoichiometry inferred from product distributions. These findings demonstrate that carboxylate-induced restructuring of Fe 3 O 4 (001) involves both surface healing and reduction processes, offering mechanistic insights relevant to ketonization and broader carboxylic acid chemistry on metal oxides.

acetic acid↗
DOE OSTI2021

Engineering Second Sphere Interactions in a Host–Guest Multicomponent Catalyst System for the Hydrogenation of Carbon Dioxide to Methanol

Many enzymes utilize interactions extending beyond the primary coordination sphere to enhance catalyst activity and/or selectivity. Such interactions could improve the efficacy of synthetic catalyst systems, but the supramolecular assemblies employed by biology to incorporate second sphere interactions are challenging to replicate in synthetic catalysts. Herein, a strategy is reported for efficiently manipulating outer sphere influence on catalyst reactivity by modulating host–guest interactions between a noncovalently encapsulated transitionmetal-based catalyst guest and a metal–organic framework (MOF) host. This composite consists of a ruthenium PNP pincer complex encapsulated in the MOF UiO-66 that is used in tandem with the zirconium oxide nodes of UiO-66 and a ruthenium PNN pincer complex to hydrogenate carbon dioxide to methanol. Due to the method used to incorporate the complexes in UiO-66, structure–activity relationships could be efficiently determined using a variety of functionalized UiO-66-X hosts. These investigations uncovered the beneficial effects of the ammonium functional group (i.e., UiO-66-NH 3 + ). Mechanistic experiments revealed that the ammonium functionality improved efficiency in the hydrogenation of carbon dioxide to formic acid, the first step in the cascade. Isotope effects and structure–activity relationships suggested that the primary role of the ammonium functionality is to serve as a general Brønsted acid. Importantly, the cooperative influence from the host was effective only with the functional group in close proximity to the encapsulated catalyst. Here, reactions carried out in the presence of molecular sieves to remove water highlighted the beneficial effects of the ammonium functional group in UiO-66-NH 3 + and resulted in a 4-fold increase in activity. As a result of the modular nature of the catalyst system, the highest reported turnover number (TON) (19 000) and turnover frequency (TOF) (9100 h –1 ) for the hydrogenation of carbon dioxide to methanol are obtained. Moreover, the reaction was readily recyclable, leading to a cumulative TON of 100 000 after 10 reaction cycles.

08 HYDROGEN↗
DOE OSTI2020

The Brachiopod δ 11 B Record Across the Carboniferous-Permian Climate Transition

In this work, we present the δ 11 B of well-preserved brachiopod fossils coupled with geochemical modeling to examine how seawater boron responded to abrupt and dynamic climate changes in the Late Paleozoic. The Late Carboniferous, a time of major coal formation and glacioeustatic sea level changes, is characterized by relatively stable brachiopod δ11B of 15–17‰, similar to values seen in modern brachiopods. Brachiopod δ 11 B dropped by ~5‰ in the early Permian and then restabilized at a new value of 10‰ within a few million years. Mass balance models of seawater δ 11 B reproduced the overall trends in our brachiopod data but failed to capture the large drop in δ11B in the early Permian. Published seawater 87 Sr/ 86 Sr and δ 44 / 40 Ca data based on brachiopod shells also shift to lower values in the early Permian, suggesting a common control on all three seawater isotope systems. The Permian terrestrial record of evaporites and eolian deposits suggests a prolonged reduced delivery of dissolved weathering products to the ocean, accounting for the change in seawater 87 Sr/ 86 Sr. This reduced weathering, in turn, led to increased atmospheric CO 2 and lowered seawater pH, which may have significantly decreased major removal mechanisms for seawater calcium and boron leading to declines in both isotope systems. We propose that boron removal via coprecipitation in carbonates and adsorption onto clay minerals was significantly diminished due to a reduction in the availability of the borate aqueous species caused by lowered seawater pH.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2026

Genetic and metabolic drivers of membrane remodeling in Clostridium thermocellum under alcohol stress

Clostridium thermocellum is a leading candidate for consolidated bioprocessing of lignocellulosic biomass into biofuels due to its native cellulolytic capabilities. Beyond ethanol, C. thermocellum is being developed as a platform for producing higher-chain alcohols such as isobutanol and n-butanol. However, its physiological adaptations to alcohol stress remain poorly understood. Here, we investigate how C. thermocellum remodels its membrane lipid composition in response to exogenous ethanol, n-butanol, isobutanol, and butyrate. Exposure to linear alcohols such as n-butanol or to organic acids like butyrate increased the proportion of straight-chain fatty acids in the membrane at the expense of branched-chain species, whereas exposure to the branched alcohol isobutanol produced the opposite effect. Isotope tracer experiments demonstrated that C. thermocellum directly incorporates the carbon backbones of exogenous alcohols and acids into fatty acids, providing a mechanistic basis for these contrasting shifts. We show that the bifunctional aldehyde/alcohol dehydrogenase AdhE is essential for the assimilation of exogenous alcohols into fatty acids, acting through its oxidative activity by first oxidizing alcohols to aldehydes and then converting them to acyl-CoA intermediates. Deletion of the pyruvate:ferredoxin oxidoreductase isozyme pfor4 abolished branched-chain fatty acid synthesis, but supplementation with isobutanol restored production, indicating that Pfor4 substitutes for the canonical branched-chain α-keto acid dehydrogenase complex. These findings reveal two distinct routes for branched-chain fatty acid production in C. thermocellum: a Pfor4-dependent pathway from α-keto acid intermediates derived from amino acid synthesis, and an AdhE-dependent salvage pathway that assimilates exogenous branched-chain alcohols.

Acetivibrio thermocellus↗
DOE OSTI2025

Berkelium–carbon bonding in a tetravalent berkelocene

Interest in actinide–carbon bonds has persisted since actinide organometallics were first investigated for applications in isotope separation during the Manhattan Project. Transplutonium organometallics are rarely isolated and structurally characterized, likely owing to limited isotope inventories, a scarcity of suitable laboratory infrastructure, and intrinsic difficulties with the anaerobic conditions required. In this paper, we report the discovery of an organometallic “berkelocene” complex prepared from 0.3 milligrams of berkelium-249. Single-crystal x-ray diffraction shows a tetravalent berkelium ion between two substituted cyclooctatetraene ligands, resulting in the formation of berkelium–carbon bonds. The coordination in berkelocene resembles that of uranocene, and calculations show that the berkelium 5f orbitals engage in covalent overlap with the δ-symmetry orbitals of the cyclooctatetraenide ligand π system. Charge transfer from the ligands is diminished relative to uranocene and other actinocenes, which maximizes contributions from the stable, half-filled 5f 7 configuration of tetravalent berkelium.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Discovery of new isotopes in the fragmentation of 82 Se and insights into their production

The production cross sections of neutron-rich nuclei for elements just above 60 Ca were measured at the Facility for Rare Isotope Beams (FRIB). Four previously unobserved isotopes ( 63 Sc, 65,66 Ti, and 68 V) were produced, separated, and identified for the first time using the Advanced Rare Isotope Separator (ARIS). One event was found to be consistent with 61 Ca . The new isotopes were created through the interaction of an 82 Se beam with a carbon target at an energy of 228 MeV/𝑢 and a primary beam current of 1.07 p⁢µ⁢A. The event-by-event particle identification of the mass number (𝐴), atomic number (𝑍), and ionic charge state (𝑞) for the reaction products was achieved by combining measurements of energy loss, time of flight, magnetic rigidity, and total kinetic energy. This successful search for new isotopes, conducted at the beginning of FRIB's third year of operation, highlights the facility's discovery potential, which will continue to grow as the beam current increases. The production cross sections were analyzed in the context of the newly developed Δ⁢𝐵⁢𝐸 systematics that provides trends in neutron-rich regions and increased sensitivity to nuclear binding, an important nuclear structure observable. Furthermore, the new systematics addresses gaps in 𝑄 𝑔 -based methods commonly used to interpret the production cross sections of light neutron-rich elements, and provides an efficient empirical approach to describe cross-section trends across isotopic chains. Good agreement with the measured data was obtained when the Δ⁢𝐵⁢𝐸 systematics and abrasion-ablation calculations were performed using the Hartree-Fock-Bogoliubov (HFB-22) mass table.

59 ≤ A ≤ 89↗
DOE OSTI2024

Terrestrial photosynthesis inferred from plant carbonyl sulfide uptake

Terrestrial photosynthesis, or gross primary production (GPP), is the largest carbon flux in the biosphere, but its global magnitude and spatiotemporal dynamics remain uncertain. The global annual mean GPP is historically thought to be around 120 PgC yr −1 , which is about 30–50 PgC yr −1 lower than GPP inferred from the oxygen-18 ( 18 O) isotope and soil respiration. This disparity is a source of uncertainty in predicting climate–carbon cycle feedbacks. Here, in this study, we infer GPP from carbonyl sulfide, an innovative tracer for CO 2 diffusion from ambient air to leaf chloroplasts through stomata and mesophyll layers. We demonstrate that explicitly representing mesophyll diffusion is important for accurately quantifying the spatiotemporal dynamics of carbonyl sulfide uptake by plants. From the estimate of carbonyl sulfide uptake by plants, we infer a global contemporary GPP of 157 (±8.5) PgC yr −1 , which is consistent with estimates from 18 O (150–175 PgC yr −1 ) and soil respiration ($149^{+29}_{-23}$) PgC yr −1 ), but with an improved confidence level. Our global GPP is higher than satellite optical observation-driven estimates (120–140 PgC yr –1 ) that are used for Earth system model benchmarking. This difference predominantly occurs in the pan-tropical rainforests and is corroborated by ground measurements, suggesting a more productive tropics than satellite-based GPP products indicated. As GPP is a primary determinant of terrestrial carbon sinks and may shape climate trajectories, our findings lay a physiological foundation on which the understanding and prediction of carbon–climate feedbacks can be advanced.

Lai, Jiameng↗
DOE OSTI2021

Analysis and Design for Irradiation of High Power TRISO Fuel Compact Specimens in HFIR

Tristructural isotropic (TRISO) fuel is being proposed for use in several high-temperature advanced reactor concepts because of its structural integrity under high operating temperatures and burnup. One of these advanced reactor concepts is the Kairos Power fluoride salt-cooled high-temperature reactor (KP- FHR) under development by Kairos Power, LLC. Previous TRISO irradiation experiments were focused on qualification for high-temperature gas reactors (HTGRs), which have higher operating temperatures but lower particle powers than the KP-FHR design. To study the performance of TRISO fuel designed for HTGRs under prototypical FHR conditions, a set of experiments was designed using the MiniFuel irradiation vehicle at the Oak Ridge National Laboratory’s (ORNL) High Flux Isotope Reactor (HFIR). The experiments will irradiate 30 TRISO-containing carbon matrix compacts at inner small vertical experiment facilities in HFIR. Each compact will contain 20 TRISO particles (600 particles total) developed for HTGRs, consisting of either 14% enriched uranium dioxide uranium carbide, naturally enriched uranium dioxide, uranium carbide, or 9.6% enriched uranium dioxide fuel kernels with time- and volume-averaged silicon carbide layer temperatures between 500 and 900°C. This report summarizes the vehicle designs that have been developed, as well as the neutronic and thermal analyses completed for these irradiation experiments. These analyses show that MiniFuel compact irradiation is a versatile experiment that can be used to study a range of TRISO particle powers and fuel types while providing reasonable separation of burnup and temperature effects.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2024

Observation of New Isotopes in the Fragmentation of Pt 198 at FRIB

Five previously unknown isotopes ( 182,183 Tm, 186,187 Yb, 190 Lu) were produced, separated, and identified for the first time at the Facility for Rare Isotope Beams (FRIB) using the Advanced Rare Isotope Separator (ARIS). The new isotopes were formed through the interaction of a 198 Pt beam with a carbon target at an energy of 186 MeV/u and with a primary beam power of 1.5 kW. Event-by-event particle identification of A, Z, and q for the reaction products was performed by combining measurements of the energy loss, time of flight, magnetic rigidity Bρ, and total kinetic energy. The ARIS separator has a novel two-stage design with high resolving power to strongly suppress contaminant beams. Finally, this successful new isotope search was performed less than one year after FRIB operations began and demonstrates the discovery potential of the facility which will ultimately provide 400 kW of primary beam power.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2025

The effects of photosynthetic rate on respiration in light, starch/sucrose partitioning, and other metabolic fluxes within photosynthesis

In the future, plants may encounter increased light and elevated CO 2 levels. How consequent alterations in photosynthetic rates will impact fluxes in photosynthetic carbon metabolism remains uncertain. Respiration in light ( R L ) is pivotal in plant carbon balance and a key parameter in photosynthesis models. Understanding the dynamics of photosynthetic metabolism and R L under varying environmental conditions is essential for optimizing plant growth and agricultural productivity. However, measuring R L under high light and high CO 2 (HLHC) conditions poses challenges using traditional gas exchange methods. In this study, we employed isotopically nonstationary metabolic flux analysis (INST-MFA) to estimate RL and investigate photosynthetic carbon flux, unveiling nuanced adjustments in Camelina sativa under HLHC. Despite numerous flux alterations in HLHC, RL remained stable. HLHC affects several factors influencing RL, such as starch and sucrose partitioning, v o /v c ratio, triose phosphate partitioning, and hexose kinase activity. Analysis of A/C i curve operational points reveals that HLHC’s major changes primarily stem from CO 2 suppressing photorespiration. Integration of these fluxes into a simplified model predicts changes in CBC labeling under HLHC. This study extends our prior discovery that incomplete CBC labeling is due to unlabeled carbon reimported during R L , offering insights into manipulating labeling through adjustments in photosynthetic rates.

Elevated CO2↗
DOE OSTI2023

Single-cell isotope tracing reveals functional guilds of bacteria associated with the diatom Phaeodactylum tricornutum

Abstract Bacterial remineralization of algal organic matter fuels algal growth but is rarely quantified. Consequently, we cannot currently predict whether some bacterial taxa may provide more remineralized nutrients to algae than others. Here, we quantified bacterial incorporation of algal-derived complex dissolved organic carbon and nitrogen and algal incorporation of remineralized carbon and nitrogen in fifteen bacterial co-cultures growing with the diatom Phaeodactylum tricornutum at the single-cell level using isotope tracing and nanoSIMS. We found unexpected strain-to-strain and cell-to-cell variability in net carbon and nitrogen incorporation, including non-ubiquitous complex organic nitrogen utilization and remineralization. We used these data to identify three distinct functional guilds of metabolic interactions, which we termed macromolecule remineralizers, macromolecule users, and small-molecule users, the latter exhibiting efficient growth under low carbon availability. The functional guilds were not linked to phylogeny and could not be elucidated strictly from metabolic capacity as predicted by comparative genomics, highlighting the need for direct activity-based measurements in ecological studies of microbial metabolic interactions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Belowground allocation and dynamics of recently fixed plant carbon in a California annual grassland

Plant roots and the organisms that surround them are a primary source for stabilized soil organic carbon (SOC). While grassland soils have a large capacity to store organic carbon (C), few field-based studies have quantified the amount of plant-fixed C that moves into soil and persists belowground over multiple years. Yet this characteristic of the soil C cycle is critical to C storage, soil water holding capacity, nutrient provisions, and the management of soil health. Here, we tracked the fate of plant-fixed C following a five-day 13 CO 2 labeling of a Northern California annual grassland, measuring C pools starting at the end of the labeling period, at three days, four weeks, six months, one year, and two years. Soil organic carbon was fractionated using a density-based approach to separate the free-light fraction (FLF), occluded-light fraction (OLF), and heavy fraction (HF). Using isotope ratio mass spectrometry, we measured 13 C enrichment and total C content for plant shoots, roots, soil, soil dissolved organic carbon (DOC), and the FLF, OLF, and HF. The chemical nature of C in the HF was further analyzed by solid state 13 C nuclear magnetic resonance (NMR) spectroscopy.

13C-NMR↗