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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Nuclear Data Sheets for A=38☆

All available experimental data of nuclear structure and decay are evaluated for the known nuclides of mass 38 (Mg, Al, Si, P, S, Cl, Ar, K, Ca, Sc, Ti). Detailed results of this evaluation are presented with the best values recommended for level energies, half-lives, γ-ray energies and intensities, decay properties (energies, intensities and placement of radiations), and other spectroscopic information. The {sup 38}Ar nuclide remains as the most extensively studied via various reactions and decays; no excited states are known in {sup 38}Al except for that an isomeric state is tentatively proposed from a recent β-decay measurement (2015St14); the {sup 38}Sc and {sup 38}Ti nuclides remain unidentified, with no experimental references reported for {sup 38}Sc and with a measurement of fragmentation cross sections reported for {sup 38}Ti but finding no evidence of its presence (1996Bl21). This work supersedes the earlier full evaluation of A=38 by J.A. Cameron and B. Singh (2008Ca01).

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Molecular insights into the differences in anti-inflammatory activities of green tea catechins on IL-1β signaling in rheumatoid arthritis synovial fibroblasts

In this study, we found that catechins found in green tea (EGCG, EGC, and EC) differentially interfere with the IL-1β signaling pathway which regulates the expression of pro-inflammatory mediators (IL-6 and IL-8) and Cox-2 in primary human rheumatoid arthritis synovial fibroblasts (RASFs). EGCG and EGC inhibited IL-6, IL-8, and MMP-2 production and selectively inhibited Cox-2 expression. EC did not exhibit any inhibitory effects. When we looked at the expression of key signaling proteins in the IL-1β signaling pathway, we found all the tested catechins could inhibit TAK-1 activity. Therefore, the consumption of green tea offers an overall anti-inflammatory effect. Molecular docking analysis confirms that EGCG, EGC, and EC all occupy the active site of the TAK1 kinase domain. However, EGCG occupies the majority of the TAK1 active site. In addition to TAK1 inhibition, EGCG can also inhibit P38 and nuclear NF-κB expression whereas EC and EGC were not effective inhibitors. Our findings suggest one of the main health benefits associated with the consumption of green tea are due to the activity of EGCG and EGC which are both present at higher amounts. Although EGCG is the most effective catechin at inhibiting downstream inflammatory signaling, its effectiveness could be hindered by the presence of EC. Therefore, varying EC content in green tea may reduce the anti-inflammatory effects of other potential catechins in green tea. - Highlights: • Catechins EC and EGC have anti-inflammatory properties in synovial fibroblasts. • EGCG is more effective at inhibiting downstream IL-1β signaling than EGC and EC. • EC content may modify green tea's anti-inflammatory effect by competing with EGCG.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Galangin ameliorates cisplatin-induced nephrotoxicity by attenuating oxidative stress, inflammation and cell death in mice through inhibition of ERK and NF-kappaB signaling

Cisplatin is a chemotherapeutic agent widely used in the treatment of various cancers. However, cisplatin can induce nephrotoxicity and neurotoxicity, limiting its dosage and usage. Galangin, a natural flavonol, has been found to exhibit anti-oxidant and anti-inflammatory effects in vivo. Here, we investigated the effects of galangin on cisplatin-induced acute kidney injury (AKI) and its molecular mechanisms in mice. Galangin administration reduced the cisplatin-induced oxidative stress by decreasing renal MDA and 3-NT formations. Galangin administration also increased renal anti-oxidative enzyme activities (SOD, GPx, and CAT) and GSH levels depleted by cisplatin. Furthermore, galangin administration inactivated stress-induced Nrf2 protein and its downstream products, HO-1 and GCLC. In terms of the inflammatory response, galangin administration reduced IκBα phosphorylation, NF-κB phosphorylation and nuclear translocation, and then inhibited cisplatin-induced secretions of pro-inflammatory TNF-α, IL-1β and IL-6. In addition, cisplatin-induced ERK and p38 phosphorylations were inhibited by galangin administration. In terms of cell death, galangin administration reduced levels of p53, pro-apoptotic Bax and activated caspase-3 to inhibit the cisplatin-induced apoptosis. Galangin administration also reduced the expression levels of RIP1 and RIP3 to inhibit cisplatin-induced RIP1/RIP3-dependent necroptosis. Therefore, galangin administration significantly ameliorates cisplatin-induced nephrotoxicity by attenuating oxidative stress, inflammation, and cell death through inhibitions of ERK and NF-κB signaling pathways. Galangin might be a potential adjuvant for clinical cisplatin therapy. - Highlights: • Galangin alleviates cisplatin-induced acute kidney injury through ERK and NF-kappaB signaling pathways. • Galangin reduces cisplatin-induced oxidative stress and inflammatory response. • Galangin suppresses cisplatin-induced cell death, apoptosis and necroptosis.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Suppression of IgE-mediated mast cell activation and mouse anaphylaxis via inhibition of Syk activation by 8-formyl-7-hydroxy-4-methylcoumarin, 4μ8C

Mast cells trigger IgE-mediated allergic reactions by releasing various allergic mediators. 8-Formyl-7-hydroxy-4-methylcoumarin, also called 4μ8C, was originally known as an inositol-requiring enzyme 1 (IRE1) suppressant, but no study has examined its relationship with mast cells and allergic diseases. Therefore, the purpose of this study was to determine whether 4μ8C is effective in suppressing allergic reactions in mast cells and in IgE-mediated allergic animal model. 4μ8C suppressed the degranulation of IgE-mediated mast cells (IC{sub 50} = 3.2 μM) and the production of cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-4 (IL-4) in a dose-dependent manner. 4μ8C also suppressed passive cutaneous anaphylaxis (PCA) in mice (ED{sub 50} = 25.1 mg/kg). In an experiment on mast cell signaling pathways stimulated by antigen, the phosphorylation and activation of Syk was decreased by 4μ8C, and phosphorylation of downstream signaling molecules, such as linker for activated T cells (LAT), Akt, and the three MAP kinases, ERK, p38, and JNK, were suppressed. Mechanistic studies showed that 4μ8C inhibited the activity of Lyn and Fyn in vitro. Based on the results of those experiments, the suppressor mechanism of allergic reaction by 4μ8C involved reduced activity of Lyn and Fyn, which is pivotal in an IgE-mediated signaling pathway. In summary, for the first time, this study shows that 4μ8C inhibits Lyn and Fyn, thus suppressing allergic reaction by reducing the degranulation and the production of inflammatory cytokines. This suggests that 4μ8C can be used as a new medicinal candidate to control allergic diseases such as seasonal allergies and atopic dermatitis. - Highlights: • Anti-allergic effect of 8-formyl-7-hydroxy-4-methylcoumarin, 4μ8C, was investigated in vitro and in vivo. • 4μ8C reversibly inhibited the degranulation of mast cells by antigen. • 4μ8C suppressed passive cutaneous anaphylaxis (PCA) in mice. • The anti-allergic effect of 4μ8C was mediated by inhibition of Lyn and Fyn in mast cells.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Quinacrine induces the apoptosis of human leukemia U937 cells through FOXP3/miR-183/β-TrCP/SP1 axis-mediated BAX upregulation

Quinacrine, which is clinically used as an antimalarial drug, has anti-cancer activity. However, mechanism underlying its cytotoxic effect remains to be completely elucidated. In the present study, we investigated the cytotoxic effect of quinacrine on human leukemia U937 cells. Quinacrine-induced apoptosis of U937 cells was accompanied with ROS generation, mitochondrial depolarization, and BAX upregulation. Quinacrine-treated U937 cells showed ROS-mediated p38 MAPK activation and ERK inactivation, which in turn upregulated FOXP3 transcription. FOXP3-mediated miR-183 expression decreased β-TrCP mRNA stability and suppressed β-TrCP-mediated SP1 degradation, thus increasing SP1 expression in U937 cells. Upregulated SP1 expression further increased BAX expression. BAX knock-down attenuated quinacrine-induced mitochondrial depolarization and increased the viability of quinacrine-treated cells. Together, our data indicate that quinacrine-induced apoptosis of U937 cells is mediated by mitochondrial alterations triggered by FOXP3/miR-183/β-TrCP/SP1 axis-mediated BAX upregulation. - Highlights: • Quinacrine induces U937 cell apoptosis via upregulation of BAX. • Quinacrine induces FOXP3 expression via p38 MAPK activation and ERK inactivation. • FOXP3-mediated miR-183 expression reduces β-TrCP mRNA stability. • Suppression of β-TrCP-mediated SP1 degradation increases BAX expression. • Quinacrine elicits FOXP3/miR-183/β-TrCP/SP1 axis-mediated BAX upregulation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

LL-37 inhibits LPS-induced inflammation and stimulates the osteogenic differentiation of BMSCs via P2X7 receptor and MAPK signaling pathway

Oral diseases, such as periapical periodontitis and periodontitis, are characterized by inflammation-induced bone loss. LL-37, a human antimicrobial peptide (AMP), has multiple biological functions and the potential to promote osteogenesis. Therefore, this study aimed to investigate the regulatory effects of LL-37 within normal and inflammatory microenvironments. The roles of P2X7 receptor (P2X7R) and mitogen-activated protein kinase (MAPK) signaling pathway were also demonstrated. The results showed that LL-37 promoted bone marrow stromal cell (BMSC) proliferation, migration and osteogenic differentiation. LL-37 inhibited the expression of the inflammatory cytokines interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and receptor activator of nuclear factor kappa-B ligand (RANKL) at both protein and gene levels, and attenuated the lipopolysaccharide (LPS)-induced inhibition of osteogenesis. Immunofluorescence (IF) confirmed P2X7R expression in BMSCs. BBG, a P2X7R antagonist, significantly attenuated LL-37-promoted osteogenesis. The phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun NH2-terminal kinase (JNK) increased after LL-37 stimulation, which did not affect p38 phosphorylation. The effects of LL-37 on osteogenesis-related gene expression were markedly attenuated by selective inhibitors of ERK1/2 and JNK. Furthermore, a mouse model of LPS-stimulated calvarial osteolysis was established, and results showed that LL-37 markedly inhibited osteoclastic bone resorption. In conclusion, we speculate that LL-37 inhibits inflammation and promotes BMSC osteogenesis via P2X7R and MAPK signaling pathway.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2017

Sensitivity to Thermonuclear Reaction Rates in Modeling the Abundance Anomalies of NGC 2419

Abundance anomalies in globular clusters provide strong evidence for multiple stellar populations within each cluster. These populations are usually interpreted as distinct generations, with the currently observed second-generation stars having formed in part from the ejecta of massive, first-generation “polluter” stars, giving rise to the anomalous abundance patterns. The precise nature of the polluters and their enrichment mechanism are still unclear. Even so, the chemical abundances measured in second-generation stars within the globular cluster NGC 2419 provide insight into this puzzling process. Previous work used Monte Carlo nuclear reaction network calculations to constrain the temperature–density conditions that could reproduce the observed abundances, thereby placing robust limits on the origins of the polluter material. The effect of individual reaction rates on these conditions has not been studied, however. Thus, we perform an exhaustive sensitivity study on the nuclear physics input to determine which reactions have the greatest impact on these predictions. We find that the {sup 30}Si(p,γ){sup 31}P, {sup 37}Ar(p,γ){sup 38}K, {sup 38}Ar(p,γ){sup 39}K, and {sup 39}K(p,γ){sup 40}Ca reactions are all critical in determining the temperature–density conditions, and ultimately, the origins of the polluter material. We conclude with recommendations for future experiments.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1971

Chemical analyses of thirty-eight iron meteorites.

The contents of nickel, cobalt, phosphorus, and carbon are tabulated for 38 iron meteorites. The samples used in the analyses are splits taken from larger samples made by milling chips from the surface of each meteorite. Individual splits from these larger samples give excellent analytical reproducibility. Previously developed criteria (Moore, Lewis, and Nava, 1969) are used to evaluate the quality of old analyses. The results of the old analyses are also tabulated.

Lewis, C. F.↗
DOE OSTI2018

Biomass production in the Lower Mississippi River Basin: Mitigating associated nutrient and sediment discharge to the Gulf of Mexico

Here, a watershed model was developed using the Soil andWater Assessment Tool (SWAT) that simulates nitrogen, phosphorus, and sediment loadings in the Lower Mississippi River Basin (LMRB). The LMRB SWAT model was calibrated and validated using 21 years of observed flow, sediment, and water-quality data. The baseline model results indicate that agricultural lands within the Lower Mississippi River Basin (LMRB) are the dominant sources of nitrogen and phosphorus discharging into the Gulf of Mexico. The model was further used to evaluate the impact of biomass production, in the presence of riparian buffers in the LMRB, on suspended-sediment and nutrient loading discharge from the Mississippi River into the Gulf of Mexico. The interplay among land use, riparian buffers, crop type, land slope, water quality, and hydrology were anlyzed at various scales. Implementing a riparian buffer in the dominant agricultural region within the LMRB could reduce suspended sediment, nitrogen, and phosphorus loadings at the regional scale by up to 65%, 38%, and 39%, respectively. Implementation of this land management practice can reduce the suspended-sediment content and improve the water quality of the discharge from the LMRB into the Gulf of Mexico and support the potential production of bioenergy and bio-products within the Mississippi River Basin.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Determination of phosphorus and sulfur in uranium ore concentrates by triple quadrupole inductively coupled plasma mass spectrometry

The analysis of impurities in a uranium ore concentrate (UOC) could provide information regarding the source, production history, and potential intended use of the UOC. This study involves the analysis of UOC samples for phosphorus and sulfur. Here, concentrations were determined by triple quadrupole inductively coupled plasma – mass spectrometry and compared with results from a pyrohydrolysis method as well as previously reported results. The sulfur and phosphorus concentrations, determined by the mass spectrometer, were used to explore possible trends in a series of UOC material, and the uncertainties were calculated using GUM workbench software. The triple quadrupole inductively coupled plasma – mass spectrometer method allows for the removal of interferences in the analysis of species.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

Mechanisms Responsible for Soil Phosphorus Availability Differences between Sprinkler and Furrow Irrigation

From a historical perspective, human‐induced soil erosion and resulting soil phosphorus (P) losses have likely occurred for thousands of years. In modern times, erosion risk and off‐site P transport can be decreased if producers convert from furrow to sprinkler irrigation, but conversion may alter nutrient dynamics. Our study goal was to determine soil P dynamics in furrow‐ (in place since the early 1900s) versus sprinkler‐irrigated (installed within the last decade) soils from four paired producer fields in Idaho. Furrow‐ and sprinkler‐irrigated soils (0–5 cm; Aridisols) contained on average 38 and 20 mg kg −1 of Olsen‐extractable P (i.e., plant‐available P), respectively; extractable P values over 40 mg kg −1 limit Idaho producers to P application based on crop uptake only. Soil samples were also analyzed using a modified Hedley extraction. Furrow‐irrigated soils contained greater inorganic P concentrations in the soluble+aluminum (Al)‐bound+iron (Fe)‐bound, occluded, and amorphous Fe‐bound pools. Phosphorus K ‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy was unable to detect Fe‐associated P but indicated greater amounts of apatite‐like or octacalcium phosphate‐like P in furrow‐irrigated producer soils, while sprinkler‐irrigated fields had lower amounts of apatite‐like P and greater proportions of P bound to calcite. Findings from a controlled USDA‐ARS sprinkler‐ versus furrow‐irrigation study suggested that changes in P dynamics occur slowly over time, as few differences were observed. Overall findings suggest that Fe redox chemistry or changes in calcium (Ca)‐associated P in flooded conditions altered P availability under furrow irrigation, even in aridic, calcareous soils, contributing to greater Olsen‐extractable P concentrations in long‐term furrow‐irrigated fields. Core Ideas Irrigation type may greatly affect soil P dynamics in calcareous systems. Furrow irrigated fields contained more plant‐available P than sprinkler irrigated fields. Furrow irrigation leads to Fe chemistry alterations, release of P, and increases available P. Available P increases under furrow irrigation could limit amendment application based on P, not N, crop needs. We still do not fully understand P dynamics in irrigated calcareous systems.

Ippolito, James A.↗
NASA NTRS1992

Modification by food of the calcium absorbability and physicochemical effects of calcium citrate

The food-calcium (Ca) interaction was examined in 12 healthy women (mean age 38 years) maintained on a constant metabolic diet. They underwent three phases of study, comprised of control (no Ca), Ca citrate (1 g Ca/day) during meals, and Ca citrate separately from meals. Each phase was 7 days in length and two 24-hour urine samples were collected on days 6 and 7. The rise from the control phase in urinary Ca was slightly more prominent when Ca citrate was given with meals than without (68 and 62%, respectively). The fall in urinary phosphorus was equivalent at about 25% between Ca citrate phases. The rise in urinary citrate and pH and the decline in urinary ammonium were more prominent when Ca citrate was given with meals; however, the changes were small or nonsignificant. The urinary saturation of Ca oxalate, brushite or monosodium urate did not differ between the two Ca citrate phases. There was a nonsignificant rise in serum iron during Ca citrate phases. The results suggest that: 1) dissolution and absorption of Ca citrate might be slightly greater when given with food than without; 2) that the ability of Ca citrate to attenuate crystallization of stone-forming Ca salts in urine is not modified by food; and 3) that Ca citrate may not impair iron absorption from food.

Non-NASA Center↗
DOE OSTI2026

Transgenic Mixed‐Linkage‐Glucan Enhancement Affects Root Characteristics and Decomposition in Soils of Contrasting Vegetation History

ABSTRACT Development of transgenic bioenergy sorghum [ Sorghum bicolor (L.) Moench] with increased contents of mixed‐linkage (1,3;1,4)‐β‐glucan (MLG) is an important step towards enhancing quality of bioenergy feedstocks. Since MLG‐enhancement leads to greater biomass digestibility, our overarching hypothesis is that root residues of MLG‐enhanced plants may be more readily decomposed in the soil, potentially creating new opportunities for optimizing soil carbon (C) sequestration, nutrient cycling, and overall agricultural sustainability. The study examined morphological, chemical, and enzymatic characteristics of fine and coarse roots of four bioenergy sorghum genotypes. Then, we incubated the roots within soils with contrasting vegetation histories while measuring C mineralization, microbial biomass C (MBC), and activity of hydrolytic enzymes and calculating vector length and vector angle enzymatic stoichiometry parameters. The results indicated that MLG‐enhancing transformations increased root total nitrogen (N) contents, decreased C/N ratios, and were associated with higher MLG concentrations in fine than in coarse roots. Incubations with transgenic roots led to 16%–38% higher MBC and 19%–41% lower microbial metabolic quotient (qCO 2 ). While enzyme activity differed markedly among the studied genotypes, it did not directly respond to MLG levels in root tissues. The increase in MBC without concurrent increases in C mineralization or hydrolytic enzyme activities in transgenic genotypes suggests that MLG enhancement promoted microbial anabolic retention of root‐derived C rather than stimulating catabolic decomposition. Enzymatic vector results indicated that these parameters reflect a variety of drivers behind microbial enzyme production, including availability of specific substrates, such as MLG here, and/or deficiency in specific nutrients, such as phosphorus (P). The study confirms the positive impacts from the roots of engineered MLG‐enhanced bioenergy plants on soil microbial activity and highlights the interactive influences on the MLG‐enhancement effects from root size and inherent soil properties.

Mahmoodabadi, Majid [Department of Plant, Soil, an↗
DOE OSTI2019

Phosphorus limits nitrogen dynamics in the O horizon of a forested watershed in Maine, USA

Anthropogenic emissions have altered the N status of northeastern USA forests, highlighting the importance of our imperfect understanding of the interaction between nitrogen and phosphorus in response to atmospheric N deposition. We investigated soil N and P dynamics at the Bear Brook Watershed in Maine, a long-term paired watershed experiment established to study ecosystem response to experimental N enrichment. One watershed (West Bear, WB) was treated bimonthly for 25 years with ammonium sulfate, and the reference East Bear (EB) received only ambient N deposition. We conducted field and laboratory studies to examine the interaction between N and P in O horizon soils in both EB and WB. In the “Pulse-Chase” Study, a field addition of 100 kg P ha-1 resulted in an overall 38% decrease in extractable ammonium (NH4+-N), due to increased immobilization. Noteworthy was that even under ambient N deposition rates, EB displayed parallel, although lower, evidence of P limitation compared to WB. In contrast, in a “Response Surface” laboratory study, soils incubated in the laboratory at rates of 0 to 200 kg P ha-1 showed increases in PNNM and NH4+-N concentrations in response to P additions. There was no effect of N-status in the Response Surface Study, but hardwood soils showed a faster response and greater rates of potential net N mineralization (PNNM) compared to softwood soils. Despite contrasting responses, both the field and laboratory studies suggested that N dynamics at BBWM were P limited, and that N status and forest type influenced the N and P interaction.

Salvino, Cayce↗
NASA NTRS2014

The Rapid Evolution of the Exciting Star of the Stingray Nebula

Context: SAO244567, the exciting star of the Stingray nebula, is rapidly evolving. Previous analyses suggested that it has heated up from an effective temperature of about 21 kK in 1971 to over 50 kK in the 1990s. Canonical post-asymptotic giant branch evolution suggests a relatively high mass while previous analyses indicate a low-mass star. Aims: A comprehensive model-atmosphere analysis of UV and optical spectra taken during 1988-2006 should reveal the detailed temporal evolution of its atmospheric parameters and provide explanations for the unusually fast evolution. Methods: Fitting line profiles from static and expanding non-LTE model atmospheres to the observed spectra allowed us to study the temporal change of effective temperature, surface gravity, mass-loss rate, and terminal wind velocity. In addition, we determined the chemical composition of the atmosphere. Results: We find that the central star has steadily increased its effective temperature from 38 kK in 1988 to a peak value of 60 kK in 2002. During the same time, the star was contracting, as concluded from an increase in surface gravity from log g = 4.8 to 6.0 and a drop in luminosity. Simultaneously, the mass-loss rate declined from log(M/M (solar mass) yr (exp −1)) = −9.0 to −11.6 and the terminal wind velocity increased from v (infinity) = 1800 km s (exp −1) to 2800 km s (exp −1). Since around 2002, the star stopped heating and has cooled down again to 55 kK by 2006. It has a largely solar surface composition with the exception of slightly subsolar carbon, phosphorus, and sulfur. The results are discussed by considering different evolutionary scenarios. Conclusions: The position of SAO244567 in the log T (sub eff) -log g plane places the star in the region of sdO stars. By comparison with stellar-evolution calculations, we confirm that SAO244567 must be a low-mass star (M < 0.55 solar mass). However, the slow evolution of the respective stellar evolutionary models is in strong contrast to the observed fast evolution and the young planetary nebula with a kinematical age of only about 1000 years. We speculate that the star could be a late He-shell flash object. Alternatively, it could be the outcome of close-binary evolution. Then SAO244567 would be a low-mass (0.354 solar mass) helium pre-white dwarf after the common-envelope phase, during which the planetary nebula was ejected.

Stingray↗
DOE OSTI2018

Phosphorus Fractionation Responds to Dynamic Redox Conditions in a Humid Tropical Forest Soil

Phosphorus (P) is a key limiting nutrient in highly weathered soils of humid tropical forests. A large proportion of P in these soils is bound to redox-sensitive iron (Fe) minerals; however, little is known about how Fe redox interactions affect soil P cycling. In an incubation experiment, we changed bulk soil redox regimes by varying headspace conditions (air versus N 2 gas) and examined the responses of soil P and Fe species to two fluctuating treatments (4- or 8-day oxic followed by 4-day anoxic) and two static redox treatments (oxic and anoxic). A static anoxic headspace increased NaOH-extractable inorganic P and ammonium oxalate-extractable total P (AO-Pt) by 10% and 38%, respectively, relative to a static oxic headspace. Persistent anoxia also increased NaHCO 3 -extractable total P (NaHCO 3 -P t ) toward the end of the experiment. Effects of redox fluctuation were more complex and dependent on temporal scales. Ammonium oxalate-extractable Fe and Pt concentrations responded to redox fluctuation early in the experiment, but not thereafter, suggesting a depletion of reductant over time. Immediately following a switch from an oxic to anoxic headspace, concentrations of AO-Pt, AO-Fe, and HCl-extractable Fe(II) increased (within 30 min) but fell back to initial levels by 180 min. Surprisingly, the labile P pool (NaHCO 3 -P t ) decreased immediately after reduction events, potentially due to resorption and microbial uptake. Overall, our data demonstrate that P fractions can respond rapidly to changes in soil redox conditions, and in environments where redox oscillation is common, roots and microbes may benefit from these rapid P dynamics.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Reactions of the ˙NO 3 radical with nuclear extraction ligands in alkane solution

Here, the reactivity of the nitrate radical (NO 3 ˙) with organophosphorus and amidic actinide and lanthanide complexing agents of interest to nuclear solvent extraction applications was measured, resulting in the first-ever reported bimolecular rate constants for this radicals’ reactions in dodecane solution. The order of reactivity for neutral organophosphorus compounds showed faster rate constants with increasing electron density on the phosphoryl phosphorus atom, indicating an increasing facility for electron abstraction reactions occurring in addition to H-atom abstraction from the ligand alkane chains. The only acidic organophosphorus compound investigated, HEH[EHP], showed low reactivity with the NO 3 ˙ radical, attributed to its dimerization in this non-polar solvent. Amide ligand reaction rates were faster than for organophosphorus molecules, suggesting more facile H-atom abstraction from carbonyl activated methylene and amyl groups. While all rate constants were slower than the diffusion-limited rate they were still rapid enough to result in significant oxidation of solvent extraction ligands in dodecane solution.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Linking soil phosphorus with forest litterfall resistance and resilience to cyclone disturbance: A pantropical meta-analysis

While tropical cyclone regimes are shifting with climate change, the mechanisms underpinning the resistance (ability to withstand disturbance-induced change) and resilience (capacity to return to pre-disturbance reference) of tropical forest litterfall to cyclones remain largely unexplored pantropically. Single-site studies in Australia and Hawaii suggest that litterfall on low-phosphorus (P) soils is more resistant and less resilient to cyclones. Here, we conducted a meta-analysis to investigate the pantropical importance of total soil P in mediating forest litterfall resistance and resilience to 22 tropical cyclones. We evaluated cyclone-induced and post-cyclone litterfall mass (g/m 2 /day), and P and nitrogen (N) fluxes (mg/m 2 /day) and concentrations (mg/g), all indicators of ecosystem function and essential for nutrient cycling. Across 73 case studies in Australia, Guadeloupe, Hawaii, Mexico, Puerto Rico, and Taiwan, total litterfall mass flux increased from ~2.5 ± 0.3 to 22.5 ± 3 g/m 2 /day due to cyclones, with large variation among studies. Litterfall P and N fluxes post-cyclone represented ~5% and 10% of the average annual fluxes, respectively. Post-cyclone leaf litterfall N and P concentrations were 21.6 ± 1.2% and 58.6 ± 2.3% higher than pre-cyclone means. Mixed-effects models determined that soil P negatively moderated the pantropical litterfall resistance to cyclones, with a 100 mg P/kg increase in soil P corresponding to a 32% to 38% decrease in resistance. Based on 33% of the resistance case studies, total litterfall mass flux reached pre-disturbance levels within one-year post-disturbance. A GAMM indicated that soil P, gale wind duration and time post-cyclone jointly moderate the short-term resilience of total litterfall, with the nature of the relationship between resilience and soil P contingent on time and wind duration. Across pantropical forests observed to date, our results indicate that litterfall resistance and resilience in the face of intensifying cyclones will be partially determined by total soil P.

59 BASIC BIOLOGICAL SCIENCES↗