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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

3D Bragg Coherent Diffraction Imaging of Extended Nanowires: Defect Formation in Highly Strained InGaAs Quantum Wells

InGaAs quantum wells embedded in GaAs nanowires can serve as compact near-infrared emitters for direct integration onto Si complementary metal oxide semiconductor technology. While the core–shell geometry in principle allows for a greater tuning of composition and emission, especially farther into the infrared, the practical limits of elastic strain accommodation in quantum wells on multifaceted nanowires have not been established. One barrier to progress is the difficulty of directly comparing the emission characteristics and the precise microstructure of a single nanowire. Here, in this study, we report an approach to correlating quantum well morphology, strain, defects, and emission to understand the limits of elastic strain accommodation in nanowire quantum wells specific to their geometry. We realize full 3D Bragg coherent diffraction imaging (BCDI) of intact quantum wells on vertically oriented epitaxial nanowires, which enables direct correlation with single-nanowire photoluminescence. By growing In 0.2 Ga 0.8 As quantum wells of distinct thicknesses on different facets of the same nanowire, we identified the critical thickness at which defects are nucleated. A correlation with a traditional transmission electron microscopy analysis confirms that BCDI can image the extended structure of defects. Finite element simulations of electron and hole states explain the emission characteristics arising from strained and partially relaxed regions. This approach, imaging the 3D strain and microstructure of intact nanowire core–shell structures with application-relevant dimensions, can aid the development of predictive models that enable the design of new compact infrared emitters.

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

Impacts of Degradation on Water, Energy, and Carbon Cycling of the Amazon Tropical Forests

Selective logging, fragmentation, and understory fires directly degrade forest structure and composition. However, studies addressing the effects of forest degradation on carbon, water, and energy cycles are scarce. Here, we integrate field observations and high-resolution remote sensing from airborne lidar to provide realistic initial conditions to the Ecosystem Demography Model (ED-2.2) and investigate how disturbances from forest degradation affect gross primary production (GPP), evapotranspiration (ET), and sensible heat flux (H). We used forest structural information retrieved from airborne lidar samples (13,500 ha) and calibrated with 817 inventory plots (0.25 ha) across precipitation and degradation gradients in the eastern Amazon as initial conditions to ED-2.2 model. Our results show that the magnitude and seasonality of fluxes were modulated by changes in forest structure caused by degradation. During the dry season and under typical conditions, severely degraded forests (biomass loss ≥66%) experienced water stress with declines in ET (up to 34%) and GPP (up to 35%) and increases of H (up to 43%) and daily mean ground temperatures (up to 6.5°C) relative to intact forests. In contrast, the relative impact of forest degradation on energy, water, and carbon cycles markedly diminishes under extreme, multiyear droughts, as a consequence of severe stress experienced by intact forests. Our results highlight that the water and energy cycles in the Amazon are driven by not only climate and deforestation but also the past disturbance and changes of forest structure from degradation, suggesting a much broader influence of human land use activities on the tropical ecosystems.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Iron mineral dissolution releases iron and associated organic carbon during permafrost thaw

It has been shown that reactive soil minerals, specifically iron(III) (oxyhydr)oxides, can trap organic carbon in soils overlying intact permafrost, and may limit carbon mobilization and degradation as it is observed in other environments. However, the use of iron(III)-bearing minerals as terminal electron acceptors in permafrost environments, and thus their stability and capacity to prevent carbon mobilization during permafrost thaw, is poorly understood. We have followed the dynamic interactions between iron and carbon using a space-for-time approach across a thaw gradient in Abisko (Sweden), where wetlands are expanding rapidly due to permafrost thaw. We show through bulk (selective extractions, EXAFS) and nanoscale analysis (correlative SEM and nanoSIMS) that organic carbon is bound to reactive Fe primarily in the transition between organic and mineral horizons in palsa underlain by intact permafrost (41.8 ±10.8 mg carbon per g soil, 9.9 to 14.8% of total soil organic carbon). During permafrost thaw, water-logging and O 2 limitation lead to reducing conditions and an increase in abundance of Fe(III)-reducing bacteria which favor mineral dissolution and drive mobilization of both iron and carbon along the thaw gradient. By providing a terminal electron acceptor, this rusty carbon sink is effectively destroyed along the thaw gradient and cannot prevent carbon release with thaw.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Emerging signals of declining forest resilience under climate change

Forest ecosystems depend on their capacity to withstand and recover from natural and anthropogenic perturbations (that is, their resilience). Experimental evidence of sudden increases in tree mortality is raising concerns about variation in forest resilience, yet little is known about how it is evolving in response to climate change. Here we integrate satellite-based vegetation indices with machine learning to show how forest resilience, quantified in terms of critical slowing down indicators, has changed during the period 2000–2020. We show that tropical, arid and temperate forests are experiencing a significant decline in resilience, probably related to increased water limitations and climate variability. By contrast, boreal forests show divergent local patterns with an average increasing trend in resilience, probably benefiting from warming and CO 2 fertilization, which may outweigh the adverse effects of climate change. These patterns emerge consistently in both managed and intact forests, corroborating the existence of common large-scale climate drivers. Reductions in resilience are statistically linked to abrupt declines in forest primary productivity, occurring in response to slow drifting towards a critical resilience threshold. Approximately 23% of intact undisturbed forests, corresponding to 3.32 Pg C of gross primary productivity, have already reached a critical threshold and are experiencing a further degradation in resilience. Together, these signals reveal a widespread decline in the capacity of forests to withstand perturbation that should be accounted for in the design of land-based mitigation and adaptation plans

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Physical characterization of fault rocks within the Opalinus Clay formation

Near-surface disposal of radioactive waste in shales is a promising option to safeguard the population and environment. However, natural faults intersecting these geological formations can potentially affect the long-term isolation of the repositories. This paper characterizes the physical properties and mineralogy of the internal fault core structure intersecting the Opalinus Clay formation, a host rock under investigation for nuclear waste storage at the Mont Terri Laboratory (Switzerland). We have performed porosity, density, microstructural and mineralogical measurements in different sections of the fault, including intact clays, scaly clays and fault gouge. Mercury intrusion porosimetry analysis reveal a gouge that has a pore network dominated by nanopores of less than 10 nm, yet a high-porosity (21%) and low grain density (2.62 g/cm 3 ) when compared to the intact rock (14.2%, and 2.69 g/cm 3 ). Thus, a more permeable internal fault core structure with respect to the surrounding rock is deduced. Further, we describe the OPA fault gouge as a discrete fault structure having the potential to act as a preferential, yet narrow, and localized channel for fluid-flow if compared to the surrounding rock. Since the fault gouge is limited to a millimetres-thick structure, we expect the barrier property of the geological formation is almost not affected.

58 GEOSCIENCES↗
DOE OSTI2022

Carcass appearance does not influence scavenger avoidance of carnivore carrion

Abstract The selection or avoidance of certain carrion resources by vertebrate scavengers can alter the flow of nutrients in ecosystems. Evidence suggests higher trophic level carrion is scavenged by fewer vertebrate species and persists longer when compared to lower trophic level carrion, although it is unclear how scavengers distinguish between carcasses of varying species. To investigate carnivore carrion avoidance and explore sensory recognition mechanisms in scavenging species, we investigated scavenger use of intact and altered (i.e., skin, head, and feet removed) coyote— Canis latrans (carnivore) and wild pig— Sus scrofa (omnivore) carcasses experimentally placed at the Savannah River Site, SC, USA. We predicted carnivore carcasses would persist longer due to conspecific and intraguild scavenger avoidance. Further, we hypothesized visually modifying carcasses would not reduce avoidance of carnivore carrion, given scavengers likely depend largely on chemical cues when assessing carrion resources. As expected, mammalian carnivores largely avoided scavenging on coyote carcasses, resulting in carnivore carcasses having longer depletion times than wild pig carcasses at intact and altered trials. Therefore, nutrients derived from carnivore carcasses are not as readily incorporated into higher trophic levels and scavengers largely depend on olfactory cues when assessing benefits and risks associated with varying carrion resources.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Top-down proteomics

Proteoforms arising from posttranslational modifications, genetic polymorphisms, and RNA splice variants, play a pivotal role as the key drivers in biology. Thus, a comprehensive understanding of proteoforms is essential for unraveling the intricacies of biological systems and bridging the gap between genotype and phenotype. By analyzing whole proteins without digestion, top-down proteomics (TDP) provides a holistic view of the proteome and presents a next-generation approach for deciphering protein function, uncovering disease mechanisms, and advancing precision medicine. This Primer embarks on a journey into the world of TDP by encapsulating its historical context, underlying principles, recent advances, and an outlook on the future of TDP. The experimental section navigates instrumentation, sample preparation, intact protein separation, tandem mass spectrometry techniques, and data collection. Results decipher raw data, visualize intact protein spectra, unravel data analysis, and explain proteoform identification, characterization, and quantitation, as well as statistical analysis. Various applications of TDP spanning the human proteoform project, biomedical, biopharmaceutical, and clinical applications are described. These are complemented by discussions on measurement reproducibility, limitations, and a forward-looking perspective outlining uncharted waters where the field can advance, and potential exciting future applications of TDP.

Roberts, David S.↗
DOE OSTI2019

Preferential interactions of primary amine-terminated quantum dots with membrane domain boundaries and lipid rafts revealed with nanometer resolution

The initial interactions of engineered nanoparticles (NPs) with living cells are governed by physicochemical properties of the NP and the molecular composition and structure of the cell membrane. Eukaryotic cell membranes contain lipid rafts – liquid-ordered nanodomains involved in membrane trafficking and molecular signaling. However, the impact of these membrane structures on cellular interactions of NPs remains unclear. Here we investigate the role of membrane domains in the interactions of primary amine-terminated quantum dots (Qdots) with liquid-ordered domains or lipid rafts in model membranes and intact cells, respectively. Using correlative atomic force and fluorescence microscopy, we found that the Qdots preferentially localized to boundaries between liquid-ordered and liquid-disordered phases in supported bilayers. The Qdots also induced holes at these phase boundaries. Using super resolution fluorescence microscopy (STORM), we found that the Qdots preferentially co-localized with lipid rafts in the membrane of intact trout gill epithelial cells – a model cell type for environmental exposures. Our observations uncovered preferential interactions of amine-terminated Qdots with liquid-ordered domains and their boundaries, possibly due to membrane curvature at phase boundaries creating energetically favorable sites for NP interactions. The preferential interaction of the Qdots with lipid rafts supports their potential internalization via lipid raft-mediated endocytosis and interactions with raft-resident signaling molecules.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Subtoxic dose of lithium cobalt oxide nanosheets impacts critical molecular pathways in trout gill epithelial cells

Increasing use of nanoscale lithium cobalt oxide (LCO) particles in nanotechnologies, including catalysis and energy storage, raises concerns over their release into the environment and subsequent biological impact. Here we study the impact of LCO nanosheets on trout gill epithelial cells – model cells for environmental exposures – by global transcriptomics using RNA-Seq. We identify molecular processes impacted by subtoxic and toxic nanoparticle (NP) doses as well as dissolved Li+ and Co2+ ions. We found that the ions, at concentrations released from the toxic NP dose, did not impact cell viability and downregulated the expression of few genes following 24 h exposure, which recovered to normal levels at 48 h. In contrast, the toxic NP dose upregulated the expression of over 1000 genes at each time point, indicating the intact NPs are responsible for perturbing gene expression and toxicity. Importantly, the subtoxic NP dose, despite having no impact on cell viability, upregulated the expression of over 500 genes at 24 h, and 150 genes at 48 h. Clustering analysis showed distinct gene expression profiles induced by the toxic and subtoxic NP doses, and functional enrichment identified pathways with distinct patterns of regulations. The impacted pathways fell into four main functional categories: metabolic and energy related processes, oxygen and hypoxia related processes, membrane binding and internalization processes, and developmental processes. Together, our observations indicate that LCO NP toxicity originates from the intact NP, not the dissolved ions, and even subtoxic NP dose impacts multiple pathways critical to the normal function of the cell.

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

Biomolecular complex viewed by dynamic nuclear polarization solid-state NMR spectroscopy

Solid-state nuclear magnetic resonance (ssNMR) is an indispensable tool for elucidating the structure and dynamics of insoluble and non-crystalline biomolecules. The recent advances in the sensitivity-enhancing technique magic-angle spinning dynamic nuclear polarization (MAS-DNP) have substantially expanded the territory of ssNMR investigations and enabled the detection of polymer interfaces in a cellular environment. This article highlights the emerging MAS-DNP approaches and their applications to the analysis of biomolecular composites and intact cells to determine the folding pathway and ligand binding of proteins, the structural polymorphism of low-populated biopolymers, as well as the physical interactions between carbohydrates, proteins, and lignin. Furthermore, these structural features provide an atomic-level understanding of many cellular processes, promoting the development of better biomaterials and inhibitors. It is anticipated that the capabilities of MAS-DNP in biomolecular and biomaterial research will be further enlarged by the rapid development of instrumentation and methodology.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Inception of electronic damage of matter by photon-driven post-ionization mechanisms

“Probe-before-destroy” methodology permitted diffraction and imaging measurements of intact specimens using ultrabright but highly destructive X-ray free-electron laser (XFEL) pulses. The methodology takes advantage of XFEL pulses ultrashort duration to outrun the destructive nature of the X-rays. Atomic movement, generally on the order of >50 fs, regulates the maximum pulse duration for intact specimen measurements. In this contribution, we report the electronic structure damage of a molecule with ultrashort X-ray pulses under preservation of the atoms' positions. A detailed investigation of the X-ray induced processes revealed that X-ray absorption events in the solvent produce a significant number of solvated electrons within attosecond and femtosecond timescales that are capable of coulombic interactions with the probed molecules. The presented findings show a strong influence on the experimental spectra coming from ionization of the probed atoms' surroundings leading to electronic structure modification much faster than direct absorption of photons. This work calls for consideration of this phenomenon in cases focused on samples embedded in, e.g., solutions or in matrices, which in fact concerns most of the experimental studies.

43 PARTICLE ACCELERATORS↗
DOE OSTI2020

Adsorption and reaction of methanol on Fe 3 O 4 (001)

The interaction of methanol with iron oxide surfaces is of interest due to its potential in hydrogen storage, and from a fundamental perspective as a chemical probe of the reactivity. We present here a study examining the adsorption and reaction of methanol on magnetite Fe 3 O 4 (001) at cryogenic temperatures using a combination of temperature programmed desorption, x-ray photoelectron spectroscopy, and scanning tunneling microscopy. We report the methanol desorption profile from Fe 3 O 4 (001) is complex, exhibiting peaks at 145, 175, 238, and 273 K, corresponding to the desorption of intact methanol, as well as peaks at 350 and 500 K due to the reaction of methoxy intermediates. The saturation of a monolayer of methanol corresponds to ~5 molecules/unit cell (u.c.), which is slightly higher than the number of surface octahedral iron atoms of 4/u.c. We probe the kinetics and thermodynamics of the desorption of molecular methanol using inversion analysis. The deconvolution of the complex desorption profile into individual peaks allows for calculations of both the desorption energy and the prefactor of each feature. The initial 0.7 methanol/u.c. reacts to form a methoxy and hydroxy intermediates by 180 K, which remains on the surface above room temperature after intact methanol has desorbed. The methoxy species react via one of two channels, a recombination reaction with surface hydroxyls to form additional methanol at ~350 K, and a disproportionation reaction to form methanol and formaldehyde at ~500 K. Only 20% of the methoxy species undergo the disproportionation reaction, with most of them reacting via the 350 K pathway.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Mass spectrometry-based technologies for probing the 3D world of plant proteins

Abstract Over the past two decades, mass spectrometric (MS)-based proteomics technologies have facilitated the study of signaling pathways throughout biology. Nowhere is this needed more than in plants, where an evolutionary history of genome duplications has resulted in large gene families involved in posttranslational modifications and regulatory pathways. For example, at least 5% of the Arabidopsis thaliana genome (ca. 1,200 genes) encodes protein kinases and protein phosphatases that regulate nearly all aspects of plant growth and development. MS-based technologies that quantify covalent changes in the side-chain of amino acids are critically important, but they only address one piece of the puzzle. A more crucially important mechanistic question is how noncovalent interactions—which are more difficult to study—dynamically regulate the proteome’s 3D structure. The advent of improvements in protein 3D technologies such as cryo-electron microscopy, nuclear magnetic resonance, and X-ray crystallography has allowed considerable progress to be made at this level, but these methods are typically limited to analyzing proteins, which can be expressed and purified in milligram quantities. Newly emerging MS-based technologies have recently been developed for studying the 3D structure of proteins. Importantly, these methods do not require protein samples to be purified and require smaller amounts of sample, opening the wider proteome for structural analysis in complex mixtures, crude lysates, and even in intact cells. These MS-based methods include covalent labeling, crosslinking, thermal proteome profiling, and limited proteolysis, all of which can be leveraged by established MS workflows, as well as newly emerging methods capable of analyzing intact macromolecules and the complexes they form. In this review, we discuss these recent innovations in MS-based “structural” proteomics to provide readers with an understanding of the opportunities they offer and the remaining challenges for understanding the molecular underpinnings of plant structure and function.

Plant Sciences↗
DOE OSTI2022

Late day measurement of excised branches results in uncertainty in the estimation of two stomatal parameters derived from response curves in Populus deltoides Bartr. x Populus nigra L.

Many terrestrial biosphere models depend on an understanding of the relationship between stomatal conductance and photosynthesis. However, unlike the measurement of photosynthetic parameters, such as the maximum carboxylation capacity, where standard methods (e.g., CO 2 response or ACi curves) are widely accepted, a consensus method for empirically measuring parameters representing stomatal response has not yet emerged. Most models of stomatal response to environment represent stomatal conductance as being bounded by a lower intercept parameter (g 0 ), and linearly scaled based on a multivariate term described by the stomatal slope parameter (g 1 ). Here we employ the widely used Unified Stomatal Optimization model, to test whether g 1 and g 0 parameters are impacted by the choice of measurement method, either on an intact branch, or a cut branch segment stored in water. We measured paired stomatal response curves on intact and excised branches of a hybrid poplar clone (Populus deltoides Bartr. x Populus nigra L. OP367), measured twice over a diurnal period. We found that predawn branch excision did not significantly affect measured g 0 and g 1 when measured within 4 h of excision. Measurement in the afternoon resulted in significantly higher values of g 1 and lower values of g0, with values changing by 55% and 56% respectively. Excision combined with afternoon measurement resulted in a marked effect on parameter estimates, with g1 increasing 89% from morning to afternoon and a 25% lower g 1 for cut branches than those measured in situ. We also show that in hybrid poplar the differences in parameter estimates obtained from plants measured under different conditions can directly impact models of canopy function, reducing modeled transpiration by 18% over a simulated 12.5-hour period. While these findings are only for a single isohydric woody species, our findings suggest that stomatal optimality parameters may not remain constant throughout the day.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

First Search for Exclusive Diphoton Production at High Mass with Tagged Protons in Proton-Proton Collisions at $\sqrt{s} = 13$

A search for exclusive two-photon production via photon exchange in proton-proton collisions, pp $\to$ p$\gamma\gamma$p with intact protons, is presented. The data correspond to an integrated luminosity of 9.4 fb$^{-1}$ collected in 2016 using the CMS and TOTEM detectors at a center-of-mass energy of 13 TeV at the LHC. Events are selected with a diphoton invariant mass above 350 GeV and with both protons intact in the final state, to reduce backgrounds from strong interactions. The events of interest are those where the invariant mass and rapidity calculated from the momentum losses of the forward-moving protons matches the mass and rapidity of the central, two-photon system. No events are found that satisfy this condition. Interpreting this result in an effective dimension-8 extension of the standard model, the first limits are set on the two anomalous four-photon coupling parameters. If the other parameter is constrained to its standard model value, the limits at 95% CL are $\lvert\zeta_1\rvert$ $\lt$ 2.9 $\times$ 10$^{-13}$ GeV$^{-4}$ and $\lvert\zeta_2\rvert$ $\lt$ 6.0 $\times$ 10$^{-13}$ GeV$^{-4}$.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Precision lattice parameter determination from transmission diffraction of thick specimens with irregular cross sections

Accurate determination of lattice parameters from X-ray diffraction requires that the diffraction angles be measured very precisely, and significant errors result if the sample–detector separation differs from that assumed. Transmission diffraction from bones, which have a complex cross section and must be left intact, is a situation where this separation is difficult to measure and it may differ from position to position across the specimen. Here, this article describes a method for eliminating the effect of variable sample cross section. Diffraction patterns for each position on the specimen are collected before and after 180° rotation about an axis normal to the cross section of interest. This places the centroid of the diffracting mass at the center of rotation and provides the absolute lattice parameters from the average apparent lattice parameters at the two rotation angles. Diffraction patterns were collected across the cross section of three specimens: a 3D-printed elliptical cylinder of Hyperelastic Bone (HB), which is composed primarily of synthetic hydroxyapatite (hAp), a 3D-printed HB model of the second metacarpal bone (Mc2), and a modern human Mc2 containing nanocrystalline carbonated apatite (cAp). Rietveld refinement was used to determine precise unit-cell parameters a apparent and c apparent for each pattern of each scan, and these values determined the actual average < a > and < c > for each sample. In conclusion, the results indicate that the 0°/180° rotation method works well enough to uncover variations approaching 1 × 10 -3 Å in cAp unit-cell parameters in intact bones with irregular cross sections.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Underwater unexploded ordnance discrimination based on intrinsic target polarizabilities – A case study

Seabed unexploded ordnance that resulted partly from the high failure rate among munitions from more than 80 years ago and from decades of military training and testing of weapons systems poses an increasing concern all around the world. Although existing magnetic systems can detect clusters of debris, they are not able to tell whether a munition is still intact requiring special removal (e.g. in situ detonation) or is harmless scrap metal. The marine environment poses unique challenges, and transferring knowledge and approaches from land to a marine environment has not been easy and straightforward. On land, the background soil conductivity is much lower than the conductivity of the unexploded ordnance and the electromagnetic response of a target is essentially the same as that in free space. For those frequencies required for target characterization in the marine environment, the seawater response must be accounted for and removed from the measurements. The system developed for this study uses fields from three orthogonal transmitters to illuminate the target and four three-component receivers to measure the signal arranged in a configuration that inherently cancels the system's response due to the enclosing seawater, the sea–bottom interface and the air–sea interface for shallow deployments. The system was tested as a cued system on land and underwater in San Francisco Bay – it was mounted on a simple platform on top of a support structure that extended 1 m below and allowed the diver to place metal objects to a specific location even in low-visibility conditions. The measurements were stable and repeatable. Furthermore, target responses estimated from marine measurements matched those from land acquisition, confirming that the seawater and air–sea interface responses were removed successfully. Thirty-six channels of normalized induction responses were used for the classification, which was done by estimating the target principal dipole polarizabilities. Our results demonstrated that the system can resolve the intrinsic polarizabilities of the target, with clear distinctions between those of symmetric intact unexploded ordnance and irregular scrap metal. The prototype system was able to classify an object based on its size, shape and metal content and correctly estimate its location and orientation.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2025

Root‐Pore Interactions, the Underestimated Driver for Rhizosphere Structure and Rhizosheath Development

Physical characteristics of rhizosphere and rhizosheath, that is, root-adhering soil, are crucial for plant performance. Yet, the drivers of the rhizosphere's structural properties and their relationships with rhizosheath development remain unclear. We used X-ray computed micro-tomography (i) to explore two drivers of rhizosphere porosity: root-induced changes vs. preferential root growth into soil with certain pore characteristics and (ii) to estimate their contributions to rhizosphere macroporosity gradients and rhizosheath formation. Rhizosheath development was assessed in relation to rhizosphere macroporosity and rhizodeposition after ¹⁴C labeling. Our results confirmed that both root-induced changes and growth preferences shape rhizosphere structure, with their relative significance depending on the inherent macropore availability. In intact soils, growth preferences were the dominant factor, while in sieved soils the root-induced changes became equally important. Rhizosheath formation was associated with roots compacting their surrounding and releasing carbon. However, no correlation was found between rhizosheath formation and the actual rhizosphere, that is, the volume of soil adjacent to the roots. The study offers new process-level understanding of rhizosphere porosity gradients, while emphasizing caution in interpreting root growth data from sieved soil studies. Similarly, traditional destructively sampled rhizosheath may not fully capture the true characteristics of the actual rhizosphere, underscoring importance of intact-soil analyses.

macroporosity gradients↗