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All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Laser spectroscopy for the study of exotic nuclei

Investigation into the properties and structure of unstable nuclei far from stability is a key avenue of research in modern nuclear physics. These efforts are motivated by the continual observation of unexpected structure phenomena in nuclei with unusual proton-to-neutron ratios. In recent decades, laser spectroscopy techniques have made significant contributions in our understanding of exotic nuclei in different mass regions encompassing almost the entire nuclear chart. This is achieved through determining multiple fundamental properties of nuclear ground and isomeric states, such as nuclear spins, magnetic dipole and electric quadrupole moments and charge radii, via the measurement of hyperfine structures and isotope shifts in the atomic or ionic spectra of the nuclei of interest. These properties offer prominent tests of recently developed state-of-the-art nuclear theory and help to stimulate new developments in improving the many-body methods and nucleon–nucleon interactions at the core of these models. With the aim of exploring more exotic short-lived nuclei located ever closer to the proton and neutron driplines, laser spectroscopy techniques, with their continuous technological developments towards higher resolution and higher sensitivity, are extensively employed at current- and next-generation radioactive ion beam facilities worldwide. Ongoing efforts in parallel promise to improve the availability of these even more exotic species at next-generation facilities. Very recently, an innovative application of laser spectroscopy on molecules containing short-lived nuclei has been demonstrated offering additional opportunities for several fields of research, e.g. fundamental symmetry studies and astrophysics. Here, in this review, the basic nuclear properties measurable with laser spectroscopy will be introduced. How these observables are associated with nuclear structure and nucleon–nucleon interactions will be discussed. Following this, a general overview of different laser spectroscopy methods will be given with particular emphasis on technical advancements reported in recent years. The main focus of this article is to review the numerous highlights that have resulted from studying exotic nuclei in different mass regions with laser spectroscopy techniques since the last edition in this series. Finally, the challenges facing the field in addition to future opportunities will be discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Chronostratigraphy of talus flatirons and piedmont alluvium along the Book Cliffs, Utah – Testing models of dryland escarpment evolution

Research on the evolution of dryland escarpments and what drives and controls their erosional retreat have been limited by a lack of chronologically constrained records. Prior investigations of escarpments in the southwestern U.S. and globally garner two endmember conceptual models -- one focused on bottom-up baselevel drivers and autogenic variations in piedmont and toeslope erosion processes, the other focused on the role of climate as a top-down forcing mechanism on sediment production and transport from cliffs. In this work, we test these conceptual models along a section of the Book Cliffs in central Utah, where climate has varied strongly and baselevel has fallen significantly over the late Quaternary. Four generations of talus flatirons and piedmont terraces are preserved in the study area we date them by optically stimulated luminescence and 10Be-exposure techniques. OSL depositional ages cluster into four generations of deposits with mean ages and mean standard errors of 117.8 ± 6.7 ka, 83.4 ± 3.3 ka, 52.4 ± 1.8 ka, and 5.6 ± 0.3 ka. 10Be-exposure results from talus boulders protruding from flatirons confirm that the youngest generation of talus is Holocene, with recent rock-fall boulders still being received on the landform top. Older flatiron generations produce incoherent, minimum exposure ages reflecting an increasing dominance of in situ boulder weathering and a steady-state denudation rate of ~45 mm/ky after tens of thousands of years. Based on the chronostratgraphy and correlation of talus and piedmont deposits, we interpret climate as the primary control on escarpment evolution. Depositional ages do not correspond to glacial epochs as historically presumed, but instead to episodes of intermediate and unstable or variable Pleistocene climate during Marine Isotope Stage-3 and 5 a/b. Results support the significance of high climate variability at millennial timescales in driving both sediment production by mass wasting from the cliff as well as sediment storage and reworking along the piedmont. In contrast, wetter climates of glacial epochs apparently caused greater erosion and sediment transport to trunk drainages. Our chronology also reveals a systematic decrease in deposit age with increasing distance up the piedmont from the regional baselevel of the Price River, consistent with transient fluvial incision and terrace abandonment. The Book Cliffs record notably does not correlate with similarly constrained records in Spain or the contrasting record from the Negev, yet they all share the feature of enhanced talus deposition and cliff retreat corresponding to climate instability rather than in response to steady glacial-climate conditions. Thus, we outline a model of escarpment evolution and retreat governed largely by top-down climate-forcing of sediment production and transport during climate variability, with local changes in baselevel and erosional processes on the piedmont being a modifying, secondary factor.

58 GEOSCIENCES↗
DOE OSTI2022

Dose conversion factors for absorbed dose in a mobile phone to absorbed dose in critical organs in an anthropomorphic phantom for emergency dosimetry applications: OSL and TL experimental results, and Monte Carlo simulations

Here, an anthropomorphic phantom was equipped with three smartphones and irradiated in five separate exposure geometries in air using a 137 Cs source. The phantom was fitted internally with thermoluminescence dosimeters (TLD-700 chips) to measure the absorbed dose to the individual organs, while the absorbed doses in the phones were evaluated using optically stimulated luminescence (OSL) from the phones’ surface mount resistors (SMRs), along with reference dosimeters, namely Luxel OSL films and TLD-700 chips. The results indicate a strong dependence on the phone location with respect to the source due to shielding and scattering from the body. Dose conversion factors were calculated for several plausible exposure scenarios in order to correlate the absorbed doses measured in the phones to the average body dose received by the phantom. The measured conversion factors were compared with calculated factors using MCNP6.2 Monte Carlo simulations and an ADAM voxel phantom. Experiments were conducted to assess how the phone orientation and angle impacts the dose received by the phone components. The overall results indicate that the doses measured can vary significantly depending upon exposure geometry (including phone position and angle). However, in rotational irradiation symmetry, the phone doses lead to an over-estimate of the average whole-body dose by an average of ~10%, independent of the phone locations tested in this study. This result, if confirmed in future studies, may be acceptable for triage.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2026

Comparison of the performance of TLD, OSL and RPL personal dosimetry systems to the American National Standard Institute (ANSI) test categories

The Laboratory Accreditation Program (LAP) tests the capability and performance of the United States Department of Energy's (USDOE) facilities to accurately measure and quantify the whole-body and extremity radiation equivalent doses to the occupational workers. The dosimetry methods used in personal dosimetry can be Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Radiophotoluminescence (RPL), among other techniques available. Currently, the TL (LiF:Mg,Ti) and OSL (Al 2 O 3 :C) dosimetry systems are DOELAP-accredited for occupational dose measurements and regulatory reporting. In this study, the performance of a beryllium oxide (BeO) OSL dosimetry system and of a silver-doped phosphate glass RPL dosimetry system is compared against the performance of an accredited LiF:Mg,Ti TL dosimetry system. The bias and standard deviation in each of the performance test categories are compared between these three systems for exposures to photons, beta, and mixed radiation fields with the criteria established by the American National Standard Institute (ANSI) and Health Physics Society (HPS) N13.11-2022 standard. The practical implementation of the dosimetry program and its equivalency to the occupational personal equivalent dose H p (0.07) and H p (10) measurements were evaluated. The TL, OSL and RPL dosimetry systems passed the ANSI performance test criteria for H p (0.07) and H p (10) occupational dose measurements and met the DOELAP accreditation requirements.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2020

Water reuse for sustainable microalgae cultivation: current knowledge and future directions

Microalgae hold great promise as environmentally sustainable sources of food, animal feed, and fuel. However, large amounts of water are used during microalgae cultivation and this negatively impacts economic viability and environmental sustainability. Reusing cultivation water can reduce the direct impacts of water usage and also reduce nutrient requirements and algal wastewater treatment. However, studies have shown that algae growth in reused water can be compromised, unaffected, or sometimes enhanced compared to controls. This review examines recent studies on water reuse to qualitatively understand these varied effects. Growth inhibitors and stimulators in reused water and their underlying mechanisms are discussed, as well as recent pre-treatment technologies and factors affecting the quality of reused water, such as microalgae taxa, culture conditions, and harvesting methods, are considered. A scheme is proposed for water reuse and harvesting methods based on the desired algal end products. Finally, taking these findings together, here we provide recommendations for further research directions as well as new insights into designing and integrating a cultivation strategy with a harvesting platform to reuse water for more efficient microalgae cultivation.

42 ENGINEERING↗
DOE OSTI2022

Spectroscopy-based isotopic (δ 13 C) analysis for high spatial resolution of carbon exchange in the rhizosphere

The rhizosphere is a highly dynamic zone bridging plant roots with needed nutrient resources in soil. While the rhizosphere may be small, it has a disproportionally large impact on plant success and biomass production. A suite of rhizosphere-hosted microbial and geochemical interactions facilitate nutrient acquisition by plant roots, and, in turn, the roots stimulate these processes by supplying organic carbon into the rhizosphere. The small physical dimensions of the rhizosphere, however, can constrain efforts to elucidate key carbon exchange processes and their spatial extent and localization. We present a method for spatially resolved δ 13 C analysis of rhizosphere samples by coupling laser ablation (LA) sampling with isotopic analysis using capillary absorption spectroscopy (CAS) which differs from conventional mass spectrometer (MS) approaches. The CAS system has high sensitivity (requires fewer nanomoles of CO 2 per analysis) than comparable MS systems, which enables reduced sample size requirements to thereby improve spatial resolution (from 25 μm to as low as a projected 5 μm spatial resolution). We demonstrate the utility of CAS using rhizosphere samples from switchgrass plants exposed to 13 CO 2 . As a result, this technique will provide a capability for tracking the extent and spatial distribution of root exudate into the rhizosphere at highly detailed spatial scales.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Root exudate composition from different plant species influences the growth of rhizosphere bacteria

Plant roots release exudates that fuel microbial activities and can structure rhizosphere microbial communities, but how different plant species use their root exudate to potentially select for different soil microbes in the rhizosphere is not well understood. Here, we investigated how root exudate from plants of three diverging lineages, Lactuca sativa (lettuce), Brassica juncea (mustard cabbage), and Zea mays (maize) influence the growth of their own rhizosphere bacteria (host) and those from other plant species (non-host) in growth bioassays. We found that on the community level, lettuce rhizosphere bacteria grew better in non-host exudate, but mustard cabbage and maize rhizosphere bacteria grew similarly well in both host and non-host exudate. However, individual bacteria taxa showed strong preferences for exudate from different plant species. The bacterial growth patterns were independent of C and N quantity, suggesting that certain exometabolic compounds may drive the growth patterns. Our results demonstrate that root exudate from a given plant species have the potential to stimulate or suppress soil bacteria and hint at a mechanism that different plant species use to select for their specific suite of rhizosphere bacteria. Furthermore, these findings contribute to our broader understanding of how root exudate quality could be a mechanism that plants use to select for distinct microbial communities in the rhizosphere.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Selenium tolerance, accumulation, localization and speciation in a Cardamine hyperaccumulator and a non-hyperaccumulator

Cardamine violifolia (family Brassicaceae ) is the first discovered selenium hyperaccumulator from the genus Cardamine with unique properties in terms of selenium accumulation, i.e., high abundance of selenolanthionine. In our study, a fully comprehensive experiment was conducted with the comparison of a non-hyperaccumulator Cardamine species, Cardamine pratensis , covering growth characteristics, chlorophyll fluorescence, spatial selenium/sulfur distribution patterns through elemental analyses (synchrotron-based X-Ray Fluorescence and ICP-OES) and speciation data through selenium K-edge micro X-ray absorption near-edge structure analysis (μXANES) and strong cation exchange (SCX)-ICP-MS. The results revealed remarkable differences in contrast to other selenium hyperaccumulators as neither Cardamine pecies showed evidence of growth stimulation by selenium. Also, selenite uptake was not inhibited by phosphate for either of the Cardamine species. Sulfate inhibited selenate uptake, but the two Cardamine species did not show any difference in this respect. However, μXRF derived speciation maps and selenium/sulfur uptake characteristics provided results that are similar to other formerly reported hyperaccumulator and non-hyperaccumulator Brassicaceae species. μXANES showed organic selenium, “C-Se-C”, in seedlings of both species and also in mature C. violifolia plants. In contrast, selenate-supplied mature C. pratensis contained approximately half “C-Se-C” and half selenate. SCX-ICP-MS data showed evidence of the lack of selenocystine in any of the Cardamine plant extracts. Thus, C. violifolia shows clear selenium-related physiological and biochemical differences compared to C. pratensis and other selenium hyperaccumulators.

Environmental Sciences & Ecology↗
DOE OSTI2020

Host tree species mediate corticolous lichen responses to elevated CO 2 and O 3 after 10 years exposure in the Aspen-FACE system

Lichens contribute significantly to the biodiversity and functioning of many ecosystems. Although lichens are useful air pollution bioindicators and may respond in significant ways to global change, they are studied infrequently under field conditions in chamberless exposure systems. We surveyed corticolous lichens on paper birch ( Betula papyrifera ) and trembling aspen ( Populus tremuloides ) after 10 years exposure (1998–2007) to elevated CO 2 (eCO 2 ) and O 3 (eO 3 ) in the Aspen-FACE experiment in Rhinelander, WI, USA. This experiment utilized chamberless exposure rings, 30 m in diameter, with both host trees planted together in one quadrant. Four treatments were allocated among 12 rings: ambient, eCO 2 , eO 3 , and the combination of eCO 2 + eO 3 , each replicated once in each of three blocks. Over the course of the experiment, ambient CO 2 increased from 343 to 386 ppm while eCO 2 averaged ~530 ppm CO 2 . Ambient ozone concentrations averaged ~37 ppb and ~49 ppb for eO 3 although exposures decreased with time. Tree growth and leaf area index were negatively affected by eO 3 and stimulated by eCO 2 , resulting in higher photosynthetically active radiation (PAR) in eO 3 and lower in eCO 2 . We assessed lichen richness and cover on five host trees per ring on the north-facing side of the trunks, which were higher on birch than on aspen. Additionally, neither of the lichen measures on birch responded to the exposure treatments, while on aspen lichen cover was highest in eO 3 and lowest in eCO 2 . On aspen, lichen cover was positively related to PAR and dominated by Caloplaca . No relationship was found for birch, although Lecanora exhibited a negative relationship with PAR. These lichens were insensitive to direct effects of eCO 2 and eO 3 at the levels applied. Instead, they responded to indirect effects, such as host tree species, and changes in understory PAR, resulting from direct effects of eO 3 and eCO 2 on the host trees.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Large seasonal fluctuations of groundwater radioiodine speciation and concentrations in a riparian wetland in South Carolina

Recent studies evaluating multiple years of groundwater radioiodine ( 129 I) concentration in a riparian wetland located in South Carolina, USA identified strong seasonal concentration fluctuations, such that summer concentrations were much greater than winter concentrations. These fluctuations were observed only in the wetlands but not in the upland portion of the plume and only with 129 I, and not with other contaminants of anthropogenic origin: nitrate/nitrite, strontium-90, technecium-99, tritium, or uranium. This unexplained observation was hypothesized to be the result of strongly coupled processes involving hydrology, water temperature, microbiology, and chemistry. To test this hypothesis, an extensive historical groundwater database was evaluated, and additional measurements of total iodine and iodine speciation were made from recently collected samples. During the summer, the water table decreased by as much as 0.7 m, surface water temperature increased by as much as 15 °C, and total iodine concentrations were consistently greater (up to 680%) than the following winter months. Most of the additional iodine observed in the summer could be attributed to proportional gains in organo-iodine, and not iodide or iodate. Furthermore, 129 I concentrations were observed to be two-orders-of-magnitude greater at the bottom of the upland aquifer than at the top. A coupled hydrological and biogeochemical conceptual model is proposed to tie these observations together. First, as the surface water temperature increased during the summer, microbial activity was enhanced, which in turn stimulated the formation of mobile organo-I. Hydrological processes were also likely involved in the observed iodine seasonal changes: (1) as the water table decreased in summer, the remaining upland water entering the wetland was comprised of a greater proportion of water containing elevated iodine concentrations from the low depths, and (2) water flow paths in summer changed such that the wells intercepted more of the contaminant plume and less of the diluting rainwater (due to evapotranspiration) and streamwater (as the lower levels promote a predominantly recharging system). Furthermore, these results underscore the importance of coupled processes influencing contaminant concentrations, and the need to assess seasonal contaminant variations to optimize long-term monitoring programs of wetlands.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Water acidification aggravates lithium-induced toxicity represented by energy supply, oxidative stress, and cell fate in Daphnia magna neonates

Lithium is extensively utilized in industrial energy production, particularly in lithium-ion batteries, and in pharmaceuticals for the treating clinical mood disorders. Consequently, lithium is frequently detected in various environmental matrices. It has been reported to cause a range of toxic effects on aquatic organisms including oxidative stress, neurological disorders, and reproductive suppression. Water acidification is a global issue with numerous negative impacts on aquatic organisms. It can alter the physio-chemical properties and bioavailability of metal ions. The acidic leaching process during lithium battery treatment and global water acidification both suggest that lithium contamination often occurs in acidic environments. In the present study, Daphnia magna neonates were exposed to four treatments (control, lithium alone, low pH, and combined) to investigate whether an acidic environment exacerbates the toxic effects of lithium on aquatic organisms and to explore potential toxic action mechanisms. The results indicated that low pH posed a significant threat to the growth and reproduction of D. magna. When exposed to both lithium and low pH, there was increased lithium accumulation and an energy trade-off response, leading to increased energy allocation to reproduction and reduced energy for growth. Lithium exposure stimulated D. magna activity, while low pH inhibited it, suggesting that an imbalance in energy consumption and supply. Combined exposure to lithium and low pH resulted in severe oxidative stress due to mitochondrial dysfunction, under-utilization of energy substances, and increased ionic homeostasis disturbances. Consequently, the exposed organism altered apoptosis and autophagy processes to maintain homeostasis. In conclusion, the present study demonstrated that lithium and water acidification posed a population-level threat to D. magna, and their combined exposure significantly largely exacerbated the toxic effects.

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTAN↗
DOE OSTI2024

Enhancing actuation control in monolithic liquid crystal elastomer films with dual heat and light responsiveness

This study presents a dual heat and light-responsive monolithic liquid crystal elastomers (LCEs) film designed to enhance actuation control. The LCE films were capable of various motion types, including curvature reversal, oscillation, and sustainable flipping. By incorporating an azobenzene compound, the films exhibited additional functionalities such as enhanced curvature reversal, accelerated oscillation, and the ability to lock continuous flipping motion upon light stimulation. Furthermore, by adjusting the aspect ratio (AR) of a single film, different thermal motion states were realized, demonstrating the flexibility of this approach. Observations using an NIR camera confirmed temperature fluctuations corresponding to thermal exchange, and the influence of UV light on motion regulation was quantitatively analyzed. In conclusion, the ability to regulate motion through dual stimuli paves the way for improved dynamic motion control and thermal management in advanced robotic applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Prevalent root-derived phenolics drive shifts in microbial community composition and prime decomposition in forest soil

Phenolic compounds perform various functions in soil ranging from microbial substrate to toxin and form the basis of several plant-mediated processes. The aim of this study was to investigate how phenolics commonly exuded by tree roots influence soil organic matter (SOM) decomposition and interact with other labile forms of carbon (C) abundant in root exudates. Therefore, we performed a 38-day incubation experiment and assessed whether phenolic compounds (benzoic acid, caffeic acid and catechin) facilitated or inhibited SOM decomposition in a glucose-amended forest soil. Changes in decomposition, substrate use, fungal and bacterial community composition, and microbial abundance and activity were measured over time using 13 C-stable-isotope tracing, DNA-based molecular methods and enzyme assays. Our findings showed that phenolics inhibited microbial activity and abundance to varying degrees. Yet, benzoic acid was the only compound producing a substantial priming effect leading to a 21% increase in SOM decomposition, which was amplified in glucose-amended soils. This stimulation in microbial activity was associated with an increase in β-1,4-glucosidase activity and the bacterial genera Paraburkholderia and Caballeronia of the Burkholderiaceae family. Phenolics drove microbial community shifts in glucose-amended soils with negligible interactive effects. In conclusion, phenolic priming of SOM decomposition is associated with microbial community shifts and amplified in the presence of glucose. This evidence emphasizes the need for considering phenolics and interactions among root exudates as priming mechanisms in the rhizosphere and other soil environments where aromatics and phenolic compounds are abundant.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Soil microbial EPS resiliency is influenced by carbon source accessibility

The adaptability of soil microbial communities to prolonged periods of drought is influenced by their ability to produce extracellular polymeric substances (EPS) with sufficient water retention properties. Microbial EPSs as water reservoirs during drought have been extensively investigated, but it remains unknown how carbon substrate accessibility to soil microbial communities will affect the chemical properties of the EPS they generate, and whether this in turn will alter their water retention ability. In this work, we observed that the accessibility of carbon substrates influenced microbial community structure and, consequently, the chemical properties of EPS produced by the microbial communities. Further, our results demonstrated that an insoluble carbon substrate (i.e., chitin), stimulated microbial communities to produce EPS with better water retention properties in comparison to a soluble carbon substrate (i.e., N-acetylglucosamine; NAG). In all, this study demonstrates the importance of carbon substrate accessibility by soil microorganisms in regulating the community structure and consequently, the EPS carbon chemistry, which in turn can greatly influence the adaptability of soil microbial communities to drought.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2023

Manganese effects on plant residue decomposition and carbon distribution in soil fractions depend on soil nitrogen availability

Recent studies have highlighted the critical role of manganese (Mn) in plant litter decomposition and soil organic carbon (C) cycling in forest ecosystems. Long term nitrogen (N) deposition and N fertilization can increase soil acidity and mobilize bioavailable Mn (Mn 2+ ) in soil. However, no studies have examined the interactive effect of N and Mn fertilization on litter decomposition and carbon distribution in agricultural soils, despite agroecosystems being subject to both N and Mn management. We hypothesized that increased soil N and Mn availability would accelerate plant residue decomposition and transfer of its C to mineral-associated organic matter (MAOM), and that the combined effect of Mn and N enrichment would be greater than the individual effect. Here, we conducted a laboratory incubation experiment by adding 13 C-labeled residue of perennial grass Glyceria striata (Lam.) to agricultural soils that had received 225 kg N ha –1 yr –1 for 27 years (N 1 ) and comparable soils that received no N (N 0 ). Before the experiment, these soils also received three levels of dissolved Mn 2+ , designated M 0 (no additional Mn), M 1 (50 mg kg –1 ), or M 2 (250 mg kg –1 ). We measured total CO 2 production as well as distribution of 13 C from the residue into CO 2 , particulate organic matter (POM), MAOM, and dissolved organic carbon (DOC) over a 1-year period. Manganese amendments significantly increased CO 2 production from residue decomposition in the N 1 soil, but no such effect was observed in the N 0 soil. Manganese also accelerated the loss of residue-derived C from POM and DOC, but increased its recovery in MAOM. However, the positive effect of added Mn in decomposition and recovery in MAOM in the presence of N fertilization occurred only during the initial 30-day decomposition period, where M 2 showed a 12% increase in cumulative CO 2 production from residue, 8% increase in POM loss, and 43% increase in recovery of residue C in MAOM compared to M 0 . For M 1 , only CO 2 emission from residue was significantly higher than Mo during this period. At 365 days M 2 showed 8% increase in CO 2 production, 1% increase in POM loss, and 16% increase in recovery of residue C in MAOM compared to M 0 , but none of these were statistically significant (p < 0.05). This study adds to the growing evidence that increasing Mn availability enhances plant litter decomposition. However, the occurrence and magnitude of Mn-induced stimulation of decomposition is context specific. Further investigation with greater temporal resolution, involving a multitude of litter and soil types and including microbial compositional and functional characterization, is recommended to fully elucidate the interactive role of Mn and N on C cycling.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Chemical identity of carbon substrates drives differences in denitrification and N 2 O reduction within agricultural soils

Rates of nitrous oxide (N 2 O) production from agricultural soils are highly variable across space and time. Improving predictions of N 2 O emissions will require improving our understanding of the drivers of denitrification and the sources of variability in the rates of N 2 O production between soils and over time. While the amount of available carbon (C) is a known control on denitrification and N 2 O reduction, relatively little attention has been paid to the effect of the chemical identity of C substrates on rates of denitrification and N 2 O reduction. We investigated the effects of twelve different C-substrate additions on the production and reduction of N 2 O in five soils taken from two distinct agricultural locations in Michigan under multiple land uses. We provided additions of glucose, cellulose, N-acetyl-glucosamine, chitin, amino acids, protein, vanillyl alcohol, lignin, citrate, succinate, methanol, and water in laboratory denitrification potential assays to determine the effects of denitrifier C preference on denitrification rates. We found that amino acids, protein, and organic acids stimulated the greatest rates of denitrification potential across all land uses. Similarly, we found these same substrates caused the most N 2 O reduction, resulting in the lowest net concentrations of N 2 O. Soils from agricultural rotations without cover crops had overall lower rates of denitrifier activity, leading to less net N 2 O production compared to soils from other land uses. In general, C-utilization patterns were similar among all soils, and C-substrate identity had a much stronger effect than land use. Here, we demonstrate that the chemical identity of available C gives rise to wide variability in rates of denitrification and N 2 O reduction.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Nitrogen addition alters the relative importance of roots and mycorrhizal hyphae in regulating soil organic carbon accumulation in a karst forest

Plant belowground carbon (C) inputs from roots and associated mycorrhizal hyphae are increasingly recognized as critical drivers impacting soil organic C (SOC) pool. However, whether roots and mycorrhizal hyphae differentially regulate SOC formation and accumulation under elevated nitrogen (N) deposition remains to be addressed. Using an ingrowth-core technique, the relative contributions of roots and mycorrhizal hyphae to SOC accumulation were distinguished and quantified in a karst forest receiving three levels of N additions (control (0 kg N ha -1 yr -1 ), low N (150 kg N ha -1 yr -1 ) and high N (300 kg N ha -1 yr -1 )). Here our results showed that N addition stimulated SOC accumulation (indicated by the increase of both bulk SOC and mineral associated organic C fraction) influenced by both roots and hyphae, especially for higher N doses. Moreover, N addition increased the contribution of the root effect relative to the hyphal effect in the SOC accrual. The correlation analysis showed that, for the hyphal effect, the change in SOC content was solely and positively correlated with the change in protective mineral phases of SOC, but not with the microbial necromass. In contrast, for the root effect, the change in SOC content was significantly and positively correlated with the changes in both soil microbial C pump efficacy and protective mineral phases of SOC. These results suggest that roots and mycorrhizal hyphae may influence the accumulation of microbial necromass and the formation of mineral-organic associations in a different magnitude under enhanced N supply. These findings advance our understanding of the root-mycorrhizal interactions in mediating SOC dynamics in forests under future N deposition scenarios.

54 ENVIRONMENTAL SCIENCES↗