Two-pool Model Research Articles

Multicompartment imaging of the brain using a comprehensive MR imaging protocol

In this study, we describe a comprehensive 3D magnetic resonance imaging (MRI) protocol designed to assess major tissue and fluid components in the brain. The protocol comprises four different sequences: 1) magnetization transfer prepared Cones (MT-Cones) for two-pool MT modeling to quantify macromolecular content; 2) short-TR adiabatic inversion-recovery prepared Cones (STAIR-Cones) for myelin water imaging; 3) proton-density weighted Cones (PDw-Cones) for total water imaging; and 4) highly T2 weighted Cones (T2w-Cones) for free water imaging. By integrating these techniques, we successfully mapped key brain components—namely macromolecules, myelin water, intra/extracellular water, and free water—in ten healthy volunteers and five patients with multiple sclerosis (MS) using a 3T clinical scanner. Brain macromolecular proton fraction (MMPF), myelin water proton fraction (MWPF), intra/extracellular water proton fraction (IEWPF), and free water proton fraction (FWPF) values were generated in white matter (WM), grey matter (GM), and MS lesions. Excellent repeatability of the protocol was demonstrated with high intra-class correlation coefficient (ICC) values. In MS patients, the MMPF and MWPF values of the lesions and normal-appearing WM (NAWM) were significantly lower than those in normal WM (NWM) in healthy volunteers. Moreover, we observed significantly higher FWPF values in MS lesions compared to those in NWM and NAWM regions. This study demonstrates the capability of our technique to volumetrically map major brain components. The technique may have particular value in providing a comprehensive assessment of neuroinflammatory and neurodegenerative diseases of the brain.

Simulated reproductive allocation to fisheries-induced evolution among small yellow croaker populations in the Yellow and Bohai Seas

Fishery-induced evolution (FIE) affects the body size and reproduction of offspring, resulting in feedback regulation of fish survival and stock recruitment. Small yellow croaker (Larimichthys polyactis) is a species of high ecological and commercial importance in the Yellow and Bohai Seas, with large fluctuations in abundance linked to overfishing and environmental changes in recent decades. To better understand the maturation size and age, threshold reproduction cost, and energy trade-offs of small yellow croaker under environmental changes (e.g. conditions) and human impacts (e.g. fishing) in the Yellow and Bohai Seas, we utilised a two-pool uncertain growth model containing the growth threshold of reproductive energy and reproductive energy cost. The results showed that for growth, maturation age, and reproduction under the baseline scenario based on field survey data from the 1950 s, when resources for small yellow croaker were underexploited, the average age was 5–6 years old and the average body length was approximately 220 mm. As the model parameters for fishing pressure and condition mortality increased, small yellow croaker tended to mature earlier, had a smaller body size, and allocated more energy to reproduction, resulting in higher population fecundity but shorter lifespan. Higher reproductive costs led to a greater proportion of reproductive energy being allocated during the spawning period, resulting in an older age of sexual maturity, shorter lifespan for spawning populations, and poor physical conditions, resulting in higher post-reproductive mortality and a limited capacity for stock recruitment. The key life-history traits of small yellow croaker, including maturity age, mean age of the population, age-specific body weight, and spawn production at different age stages, can change under different conditions. The model represents the main life history strategies and energy allocation characteristics of small yellow croaker. The simulated age and body size were within the observed range and the predicted fecundity aligned with the observed values. This study provides a prediction tool for protecting the spawning and recruitment of small yellow croaker and establishes a biological reference for sustainable management of small yellow croaker populations in the Yellow and Bohai Seas in the future.

Stronger negative priming effect and lower basal respiration rates in nutrient-poor as compared to nutrient-rich forestry-drained peatland.

Land-use changes, e.g., forestry drainage, modify the characteristics of peatland soil and affect the peatland carbon (C) balance. Peat soil nutrient status, related mainly to the original peatland type, also has an impact on the C balance after drainage, as observed earlier at the ecosystem scale for two forestry-drained sites in Southern Finland. Here the aim was to compare the soil CO2 fluxes from the two sites, nutrient-poor and nutirent-rich forestry-drained peatlands, and study the effect of plant photosynthates on the decomposition of peat C. Therefore, the respiration rates and priming effect (PE) of peat soils with variable nutrient status were examined in the laboratory. Half of the samples were labelled with 13 C-glucose to study the effect of fresh C addition on the soil decomposition. The 13 CO2 -samples were analysed with isotope ratio mass spectrometry. A two-pool mixing model was applied to separate the soil- and sugar-derived respirations and to determine the PE. The nutrient-rich peat soil respired generally more than the nutrient-poor peat. A negative PE was observed in both peat soils, suggesting that the addition of fresh C did not increase the soil decomposition, but on the contrary decreased it. The negative PE was significantly more pronounced in nutrient-poor peat soil than in the nutrient-rich peat treatments, suggesting that the higher nutrient availability suppresses the negative PE. These results imply that microbes prefer utilizing fresh C instead of old C in the short term and that the peat decomposition is suppressed in the presence of fresh C inputs from vegetation at forestry-drained peatlands. These effects are even stronger in peat soils with less nutrients available. Ecosystem scale and soil process models could be improved with the help of these results.

Rapid whole-brain quantitative MT imaging

PurposeTo provide a robust whole-brain quantitative magnetization transfer (MT) imaging method that is not limited by long acquisition times. MethodsTwo variants of a spiral 2D interleaved multi-slice spoiled gradient echo (SPGR) sequence are used for rapid quantitative MT imaging of the brain at 3 T. A dual flip angle, steady-state prepared, double-contrast method is used for combined B1 and-T1 mapping in combination with a single-contrast MT-prepared acquisition over a range of different saturation flip angles (50 deg to 850 deg) and offset frequencies (1 kHz and 10 kHz). Five sets (containing minimum 6 to maximum 18 scans) with different MT-weightings were acquired. In addition, main magnetic field inhomogeneities (ΔB0) were measured from two Cartesian low-resolution 2D SPGR scans with different echo times. Quantitative MT model parameters were derived from all sets using a two-pool continuous-wave model analysis, yielding the pool-size ratio, F, their exchange rate, kf, and their transverse relaxation time, T2r. ResultsWhole-brain quantitative MT imaging was feasible for all sets with total acquisition times ranging from 7:15 min down to 3:15 min. For accurate modeling, B1-correction was essential for all investigated sets, whereas ΔB0-correction showed limited bias for the observed maximum off-resonances at 3 T. ConclusionThe combination of rapid B1-T1 mapping and MT-weighted imaging using a 2D multi-slice spiral SPGR research sequence offers excellent prospects for rapid whole-brain quantitative MT imaging in the clinical setting.

Development of DNDC-BC model to estimate greenhouse gas emissions from rice paddy fields under combination of biochar and controlled irrigation management

Simulating the impacts of biochar and controlled irrigation (CI, a water-saving irrigation technology without surface ponding of water) combination on greenhouse gas (GHG) emissions from paddy fields is crucial, however, the original DNDC model is not capable of capturing these management impacts on emissions. In this study, we have created a new modelling approach called DNDC-Biochar-Controlled Irrigation (DNDC-BC) by adding two modules to the original DNDC: the water balance principle, and the two-pool biochar model. The performance of the DNDC-BC was tested and validated using a two-year field experiment, designed with two irrigation treatments (flood irrigation (FI), and CI) and three biochar application rates (0, 20, and 40 t ha−1), carried in the Lake Taihu region, China. Results revealed that the DNDC-BC model performed satisfactorily in simulating impacts of biochar-CI combination on emissions of CH4, N2O, SOC, and grain yield. The corresponding R2 values of DNDC-BC increased by 22.63%-35.66%, 43.00%-71.26%, 1.06%-60.87% and 15.38%-34.78% compared with those of the original model. Sensitivity analysis for the DNDC-BC showed that CH4 emissions were most sensitive to rainfall and irrigation; N2O emissions were sensitive to rainfall, irrigation and N fertilizer application rate, and SOC was sensitive to biochar application rates. Our results suggest that the combination of biochar- and CI can save water resources and mitigate GHG emissions without detrimental impacts on rice yield. The DNDC-BC can be used to estimate the long-term impacts of biochar-CI combination on GHG emission, crop productivity and climate change.

Soil contamination by diesel fuel destabilizes the soil microbial pools: Insights from permafrost soil incubations

Arctic contamination by diesel fuel (DF) is of great concern because of the uncertain feedback of permafrost carbon (C) and soil microbiota to DF in the context of climate change in high latitudes. We conducted a laboratory incubation experiment with a gradient of DF addition ratios to examine the responses of the soil microbiota of the typical permafrost soils in the tundra ecosystems of the Norilsk region (Siberia). The study revealed initial heterogeneity in the microbial activity of the studied soils (Histic Gleyic Cryosols (CR-hi,gl), Turbic Cryosols (CR-tu), Turbic Spodic Folic Cryosols (CR-tu,sd,fo), Gleyic Fluvisols (FL-gl)). We applied the two-pool model for evaluation of the effect of DF on the proportions of C pools and revealed significant differences between soil types in the fast and slow C pools in response to DF addition. The results showed that DF addition treatments had varying effects on the fast and slow C pools, microbial activity, and microbial community structure in the studied soils. For minor exceptions, DF dramatically accelerated C loss from the slow C pool in all soil types. We assume that differences in C pool and microbiota responses to DF addition were caused by soil texture and changes in microbial community structure. We isolated Serratia proteamaculans, S. liquefaciens, S. plymuthica, Rhodococcus erythropolis, Pseudomonas antarctica, P. libanensis, P. brassicacearum, and P. chlororaphis from the DF-polluted soils. These species are recommended for bioremediation to mitigate the DF contamination of permafrost soils, especially regarding climate change and the sustainable well-being of Arctic ecosystems.

Methane emissions and 13C composition from beef steers consuming binary C3-C4 diets.

Improvements in forage nutritive value can reduce methane emission intensity in grazing ruminants. This study was designed to evaluate how the legume rhizoma peanut (Arachis glabrata; RP) inclusion into bahiagrass (Paspalum notatum) hay diets would affect intake and CH4 production in beef steers. We also assessed the potential to estimate the proportion of RP contribution to CH4 emissions using δ13C from enteric CH4. Twenty-five Angus-crossbred steers were randomly allocated to one of five treatments (five steers per treatment blocked by bodyweight): 1) 100% bahiagrass hay (0%RP); 2) 25% RP hay + 75% bahiagrass hay (25%RP); 3) 50% RP hay + 50% bahiagrass hay (50%RP); 4) 75% RP hay + 25% bahiagrass hay (75%RP); 5) 100% RP hay (100%RP). The study was laid out using a randomized complete block design, and the statistical model included fixed effect of treatment, and random effect of block. Methane emissions were collected using sulfur hexafluoride (SF6) technique, and apparent total tract digestibility was estimated utilizing indigestible neutral detergent fiber as an internal marker. A two-pool mixing model was used to predict diet source utilizing CH4 δ13C. Inclusion of RP did not affect intake or CH4 production (P > 0.05). Methane production per animal averaged 250 g CH4/d and 33 g CH4/kg dry matter intake, across treatments. The CH4 δ13C were -55.5, -60.3, -63.25, -63.35, and -68.7 for 0%RP, 25%RP, 50%RP, 75%RP, and 100%RP, respectively, falling within the reported ranges for C3 or C4 forage diets. Moreover, there was a quadratic effect (P = 0.04) on the CH4 δ13C, becoming more depleted (e.g., more negative) as the diet proportion of RP hay increased, appearing to plateau at 75%RP. Regression between predicted and observed proportions of RP in bahiagrass hay diets based on δ13C from CH4 indicate δ13C to be useful (Adj. R2 = 0.89) for predicting the contribution of RP in C3-C4 binary diets. Data from this study indicate that, while CH4 production may not always be reduced with legume inclusion into C4 hay diets, the δ13C technique is indeed useful for tracking the effect of dietary sources on CH4 emissions.

Lipid droplets, the Holy Grail of hepatic stellate cells: In health and hepatic fibrosis.

Lipid droplets (LDs) are distinct morphological markers of hepatic stellate cells (HSCs). They are composed of a core of predominantly retinyl esters and triacylglycerols surrounded by a phospholipid layer; the latter harbors perilipins 2, 3, and 5, which help control LD lipolysis. Electron microscopy distinguishes between Types I and II LDs. Type I LDs are surrounded by acid phosphatase-positive lysosomes, which likely digest LDs. LD count and retinoid concentration are modulated by vitamin A intake. Alcohol consumption depletes hepatic retinoids and HSC LDs, with concomitant transformation of HSCs to fibrogenic myofibroblast-like cells. LD loss and accompanying HSC activation occur in HSC cell culture models. Loss of LDs is a consequence of and not a prerequisite for HSC activation. LDs are endowed with enzymes for synthesizing retinyl esters and triacylglycerols as well as neutral lipases and lysosomal acid lipase for breaking down LDs. HSCs have two distinct metabolic LD pools: an "original" pool in quiescent HSCs and a "new" pool emerging in HSC activation; this two-pool model provides a platform for analyzing LD dynamics in HSC activation. Besides lipolysis, LDs are degraded by lipophagy; however, the coordination between and relative contributions of these two pathways to LD removal are unclear. While induction of autophagy accelerates LD loss in quiescent HSCs and promotes HSC activation, blocking autophagy impairs LD degradation and inhibits HSC activation and fibrosis. This article is a critique of five decades of investigations into the morphology, molecular structure, synthesis, and degradation of LDs associated with HSC activation and fibrosis.

Exclusion of plant input affects the temperature sensitivity of soil organic carbon decomposition

Plant residue input plays a vital role in cropland carbon (C) balance, which can be greatly affected by climate change. Our knowledge of the effect of plant residue on soil respiration is crucial for evaluating C exchange between the atmosphere and terrestrial ecosystems, but large uncertainties remain in the effect of plant input on the temperature sensitivity (Q10) of soil organic C (SOC) decomposition in cropland ecosystems. Here, soils were sampled from two bare fallow plots (including a Mollisol and an Alfisol with different climate and land-use history) and their adjacent old field plots, and were incubated at 10 °C and 20 °C for 815 days. The ‘equal-time’, ‘equal-C’, ‘one-pool model’ and ‘two-pool model’ methods were used to evaluate the Q10 of SOC decomposition. Results indicated that in the early stage of incubation, exclusion of plant input increased the Q10 (Alfisol) or had minor effect on the Q10 (Mollisol), which may be related to the interactions between substrate quality decrease (increase of chemical stability) and clay mineral suppression on microbial decomposition. However, in the later stage of incubation, plant residue removal decreased the Q10 values in both soils possibly due to the limitation of substrate availability on microbial decomposition. Overall, the role of plant input in the temperature sensitivity of SOC decomposition should be considered when predicting SOC stocks in a future warmer world.

B0 Correction for 3T Amide Proton Transfer (APT) MRI Using a Simplified Two-Pool Lorentzian Model of Symmetric Water and Asymmetric Solutes.

Amide proton transfer (APT)-weighted MRI is a promising molecular imaging technique that has been employed in clinic for detection and grading of brain tumors. MTRasym, the quantification method of APT, is easily influenced by B0 inhomogeneity and causes artifacts. Current model-free interpolation methods have enabled moderate B0 correction for middle offsets, but have performed poorly at limbic offsets. To address this shortcoming, we proposed a practical B0 correction approach that is suitable under time-limited sparse acquisition scenarios and for B1 ≥ 1 μT under 3T. In this study, this approach employed a simplified Lorentzian model containing only two pools of symmetric water and asymmetric solutes, to describe the Z-spectral shape with wide and ‘invisible’ CEST peaks. The B0 correction was then performed on the basis of the fitted two-pool Lorentzian lines, instead of using conventional model-free interpolation. The approach was firstly evaluated on densely sampled Z-spectra data by using the spline interpolation of all acquired 16 offsets as the gold standard. When only six offsets were available for B0 correction, our method outperformed conventional methods. In particular, the errors at limbic offsets were significantly reduced (n = 8, p < 0.01). Secondly, our method was assessed on the six-offset APT data of nine brain tumor patients. Our MTRasym (3.5 ppm), using the two-pool model, displayed a similar contrast to the vendor-provided B0-orrected MTRasym (3.5 ppm). While the vendor failed in correcting B0 at 4.3 and 2.7 ppm for a large portion of voxels, our method enabled well differentiation of B0 artifacts from tumors. In conclusion, the proposed approach could alleviate analysis errors caused by B0 inhomogeneity, which is useful for facilitating the comprehensive metabolic analysis of brain tumors.

Unconscious priming shares a common resource pool with the manipulation subsystem.

BackgroundWorking memory can be subdivided into two relatively independent subordinate systems, the maintenance subsystem and the manipulation subsystem. Although the two subsystems are quite heterogeneous, research thus far has not adequately distinguished the resource pools of the two subsystems. Additionally, previous research on the relationship between working memory and unconscious priming is paradoxical. Different subsystems leading to different effects on unconscious priming might be the reason for the paradoxical research. Therefore, the current article aimed to distinguish the resource pools among two working-memory subsystems and to investigate the relationship between the two subsystems and unconscious priming.MethodsTo address these issues, a maintenance dual-task and a manipulation dual-task program were developed. Each participant had to separately perform the two dual tasks in a balanced order. In each dual task, participants first completed a masked priming task accompanied by working-memory load. As a control, participants completed a prime identification test to confirm that the processing of the masked prime was at the unconscious level. The maintenance dual task comprised sandwich masking trials accompanied by Sternberg trials, while the manipulation dual task comprised sandwich masking trials accompanied by N-back trials.ResultsThe results of the prime identification test indicated that the participants could not consciously perceive the masked prime of both dual tasks. The results of the working-memory task of both dual tasks indicated that the load manipulation was successful for both dual tasks. Most importantly, the results of the masking task of both dual tasks showed that an increase in working-memory load decreased the magnitude of unconscious priming in the manipulation dual task, whereas an increase in working-memory load did not decrease unconscious priming in the maintenance dual task. These observations demonstrate that the manipulation subsystem, rather than the maintenance subsystem, interferes with unconscious priming. Together with previous research, we propose a two-pool attention resource model to explain the modulation of working memory on unconscious priming by dissociating the executive resource pool of the manipulation system from the retention resource pool of the maintenance system. Thus, the current work confirms and extends the extant literature about the dependence of unconscious processing on attention resources by suggesting that unconscious priming shares a common resource pool with the manipulation subsystem.

Implementation of the QRAPMASTER data analysis using dictionary matching and quantitative evaluation of the magnetization transfer effect

PurposeTo clarify the magnetization transfer (MT) effect on T1 and T2 values obtained with the QRAPMASTER sequence. MethodsA phantom consisting of MnCl2 aqueous solution with various proton relaxation times and a chicken breast sample was imaged with the QRAPMASTER sequence and a multislice multiple spin-echo (MSMSE) sequence that was the basis of the QRAPMASTER sequence using a 1.5 T MRI system. T1 values were calculated by data matching using the dictionary dataset created by a Bloch image simulation of the QRAPMASTER sequence. T2 values were calculated by data matching using the dictionary dataset created by a Bloch image simulation of the MSMSE sequence. The MT effect on the images acquired with the QRAPMASTER and MSMSE sequences was calculated by numerically solving Bloch equations using a two-pool model. ResultsThe linearity and accuracy of the regression lines between the T1 values measured by the QRAPMASTER sequence and those measured by the standard method excluding the T1 values of the chicken breast sample was excellent (R = 0.9969–0.9986, slope = 1.0065–1.016) for consecutive four slices including the central slice. The linearity of the regression lines for the T2 values of all samples was good (R = 0.963–0.985) for the four slices. The accuracy of the regression line was not good (slope = 0.674–0.758), which was mainly due to the effect of eddy currents. The large deviation of the T1 values of the chicken breast sample from the regression line was semi-quantitatively reproduced by the Bloch simulation for the two-pool model. ConclusionThis study demonstrated that the T1 value of a biological sample obtained by the QRAPMASTER sequence was shortened by the MT effect.

Spent coffee grounds by-products and their influence on soil C–N dynamics

SCG are a bio-waste generated in great amount worldwide which are attractive as soil amendment for their high content of organic matter and nutritive elements. Nevertheless, several studies have shown that soil application of untreated SCG has detrimental agronomic and environmental effects due to their high degradability and content of noxious compounds (phenols, caffeine, and tannins). However, SCG can be valorised, in the frame of circular economy, by extraction of energy and valuable products (carbohydrates, proteins, bio-oil, bio-diesel) and generation of solid by products (biochar, hydrochar, compost) that can be utilized as soil fertilizers and amendments.Therefore, the aim of this work was the characterization of different solid SCG by-products (as second-generation products) and their assessment as effective organic amendments. The novelty of this study is that for the first time 8 different by-products derived from the same SCG were characterized and comparatively evaluated for their impact on the C and N cycles of soil. SCG was collected and treated to generate 8 different SCG by-products (biochars produced at 270 and 400 °C, hydrochars produced at 160 and 200 °C, vermicompost, defatted SCG and biochars produced from defatted SCG at 270 and 400 °C). SCG and derived by-products were characterized for SEM micromorphology, pH and EC values, and C, N, H, O, volatile matter, fixed C, LOI, carbonates, water soluble C and N, NO3− and NH4+ content. SCG and SCG by-products assessment as organic amendments was performed with an incubation experiment. The residues were added (2.5%) to a moist Mediterranean agricultural soil and the amended soil samples were placed in mesocosms and incubated at 20 °C for 30 days. During incubation, CO2 and N2O emissions were measured every 6 h by means of a gas chromatography automated system for GHG sampling and measurement. The percentage of added C remaining (CR) in the soil was calculated by fitting the cumulative respiration of amended soil to a two-pool model. After 2, 7 and 30 days of incubation, the control and amended soils were sampled and analyzed for their content of extractable organic C, N, NO3− and NH4+ and microbial biomass C and N. Results showed that SCG by-products presented a great variability in their properties. SCG and hydrochars presented higher contents in volatile matter and water soluble C and N, and low content of fixed C, while biochars showed an opposite behaviour. SEM images confirmed the different characteristics of the SCG by-products: the biochar presented a porous structure, honeycomb-like form, due to the loss of the more soluble compounds, while the SCG and hydrochars' pores were filled with amorphous carbonaceous materials. Consequently, soil addition of SCG by-products showed a distinct impact on C and N cycle and microbial biomass content. Addition of SCG and hydrochars generated the highest cumulative CO2–C emissions (2103–2300 μg g−1), the lower amount of CR (86.8–88.6%), increased the soil extractable organic C and microbial biomass C and N and caused N immobilization. On the other hand, the addition of biochars generated lower CO2–C emissions (542–1060 μg g−1), higher amounts of CR (96. 3–99.9%) and lower amounts of extractable compounds and microbial biomass C and N, generating also N immobilization, but to a lesser extent. The addition of vermicompost generated 723 μg g−1 of CO2–C and 98% of CR remaining. However, this by-product did not generate N immobilization being able to act as N fertilizer. None of the residues generated N2O emissions. The different properties of the SCG by-products and their impact on C and N cycle indicated that they can be effectively applied to soil to exert different agronomical and environmental functions.

Effects of Bamboo (Phyllostachys praecox) Cultivation on Soil Nitrogen Fractions and Mineralization

The mineralization of soil organic nitrogen (N) is the key process in the cycling of N in terrestrial ecosystems. Land-use change to bamboo (Phyllostachys praecox) cultivation that later entails organic material mulching combined with chemical fertilizer application will inevitably influence soil N mineralization (Nmin) and availability dynamics. However, the soil Nmin rates associated with various N fractions of P. praecox in response to land-use change and mulching are not well understood. The present study aimed to understand the effects of land-use change to P. praecox bamboo cultivation and organic material mulching on soil Nmin and availability. Soil properties and organic N fractions were measured in a P. praecox field planted on former paddy fields, a mulched P. praecox field, and a rice (Oryza sativa L.) field. Soil Nmin was determined using a batch incubation method, with mathematical models used to predict soil Nmin kinetics and potential. The conversion from a paddy field to P. praecox plantation decreased the soil pH, soil total N, and soil organic matter (SOM) content significantly (p &lt; 0.05); the mulching method induced further soil acidification. The mulching treatment significantly augmented the SOM content by 7.08% compared with the no-mulching treatment (p &lt; 0.05), but it decreased soil hydrolyzable N and increased the nonhydrolyzable N (NHN) content. Both the Nmin rate and cumulative mineralized N were lowest in the mulched bamboo field. The kinetics of Nmin was best described by the ‘two-pool model’ and ‘special model’. The Pearson’s correlation analysis and the Mantel test suggested soil pH was the dominant factor controlling the soil cumulative mineralized N and mineralization potential in the bamboo fields. These findings could help us better understand the N cycling and N availability under mulching conditions for shifts in land use, and provide a scientific basis for the sustainable management of bamboo plantations.

Implications of the Thermodynamic Response of Soil Mineralization, Respiration, and Nitrification on Soil Organic Matter Retention.

Considerable research has shown that modifications in global temperature regimes can lead to changes in the interactions between soil respiration and the sequestration of C and N into soil organic matter (SOM). We hypothesized that despite the interconnected nature of respiration, net N mineralization, and nitrification processes, there would be differences in their thermodynamic responses that would affect the composition of inorganic soil N and the potential for retention of N in SOM. To test this hypothesis, soil respiration, N mineralization and nitrification responses were evaluated during constant temperature incubations at seven temperatures (4–42°C) in tilled and no-till soils from two major agroecological zones in Oregon; Willamette Valley, and Pendleton located in the Columbia River Basin. We observed (1) significant thermodynamic differences between the three processes in all soils, (2) a distinctly different thermodynamic profile in Willamette vs. Pendleton, and (3) a dynamic response of Topt (optimal temperature for activity), and Tsmax (temperature of greatest rate response to temperature), and temperature sensitivity (Δ) over the incubation time course, resulting in shifts in the thermodynamic profiles that could not be adequately explained by changes in process rates. We found that differences in contributions of ammonia oxidizing archaea and bacteria to nitrification activity across temperature helped to explain the thermodynamic differences of this process between Willamette and Pendleton soils. A two-pool model of SOM utilization demonstrated that the dynamic thermodynamic response of respiration in the soils was due to shifts in utilization of labile and less-labile pools of C; and that the respiration response by Pendleton soils was more dependent upon contributions from the less-labile C pool resulting in higher Topt and Tsmax than Willamette soils. Interestingly, modeling of N mineralization using the two-pool model suggested that only the less-labile pool of SOM was contributing to N mineralization at most temperatures in all soils. The difference in labile and less-labile SOM pool utilization between respiration and N mineralization may suggest that these processes may not be as interconnected as previously thought.

In Vivo Estimation of Ketogenesis Using Metabolic Flux Analysis-Technical Aspects and Model Interpretation.

Ketogenesis occurs in liver mitochondria where acetyl-CoA molecules, derived from lipid oxidation, are condensed into acetoacetate (AcAc) and reduced to β-hydroxybutyrate (BHB). During carbohydrate scarcity, these two ketones are released into circulation at high rates and used as oxidative fuels in peripheral tissues. Despite their physiological relevance and emerging roles in a variety of diseases, endogenous ketone production is rarely measured in vivo using tracer approaches. Accurate determination of this flux requires a two-pool model, simultaneous BHB and AcAc tracers, and special consideration for the stability of the AcAc tracer and analyte. We describe the implementation of a two-pool model using a metabolic flux analysis (MFA) approach that simultaneously regresses liquid chromatography-tandem mass spectrometry (LC-MS/MS) ketone isotopologues and tracer infusion rates. Additionally, 1H NMR real-time reaction monitoring was used to evaluate AcAc tracer and analyte stability during infusion and sample analysis, which were critical for accurate flux calculations. The approach quantifies AcAc and BHB pool sizes and their rates of appearance, disposal, and exchange. Regression analysis provides confidence intervals and detects potential errors in experimental data. Complications for the physiological interpretation of individual ketone fluxes are discussed.

Quantitative 3D Ultrashort Echo Time Magnetization Transfer Imaging for Evaluation of Knee Cartilage Degeneration In Vivo.

Recent studies suggest that macromolecular fraction (MMF) derived from three-dimensional ultrashort echo time magnetization transfer (UTE-MT) imaging is insensitive to the magic angle effect. However, its clinical use in osteoarthritis (OA) remains to be investigated. To investigate the feasibility of 3D UTE-MT-derived MMF in differentiating normal from degenerated cartilage. Prospective. Sixty-two participants (54.8 ± 16.7 years, 30 females) with and without OA, plus two healthy volunteers (mean age 35.0 years) for reproducibility test. 3 T/UTE-MT sequence. A 3D UTE-MT sequence was employed to calculate MMF based on a two-pool model. Kellgren-Lawrence (KL) grade and Whole-Organ Magnetic Resonance Imaging Score (WORMS) were evaluated by three experienced musculoskeletal radiologists. KL grade was condensed into three groups: KL0, KL1-2, and KL3-4. WORMS was regrouped based on extent of lesion (extent group) and depth of lesion (depth group), respectively. The performance of MMF at evaluating the degeneration of cartilage was assessed via Spearman's correlation coefficient and the area under the curve (AUC) calculated according to the receiver-operating characteristic curve. After normality check, one-way analysis of variance was used to evaluate the performance. Tukey-Kramer test was performed for post hoc testing. MMF showed significant negative correlations with KL grade (r=-0.53, P < 0.05) and WORMS (r=-0.49, P < 0.05). Significantly lower MMFs were found in subjects with greater KL grade (11.8 ± 0.8% for KL0; 10.9 ± 0.9% for KL1-2; 10.6 ± 1.1% for KL3-4; P < 0.05) and in cartilage with greater extent (12.1 ± 1.6% for normal cartilage; 10.9 ± 1.6% for regional lesions; 9.6 ± 1.7% for diffuse lesions; P < 0.05) and depth (12.1 ± 1.6% for normal cartilage; 10.6 ± 1.6% for partial-thickness lesions; 8.8 ± 1.7% for full-thickness lesions; P < 0.05) of lesions. AUC values of MMF for doubtful-minimal OA (KL1-2) and mild cartilage degradation (WORMS1-2) were 0.8 and 0.7, respectively. This study highlights the clinical potential of MMF in the detection of early OA. 2 TECHNICAL EFFICACY STAGE: 2.

Temperature sensitivity of SOM decomposition is linked with a K-selected microbial community.

Temperature sensitivity (Q10 ) of soil organic matter (SOM) decomposition is a crucial parameter to predict the fate of soil carbon (C) under global warming. Nonetheless, the response pattern of Q10 to continuous warming and the underlying mechanisms are still under debate, especially considering the complex interactions between Q10 , SOM quality, and soil microorganisms. We examined the Q10 of SOM decomposition across a mean annual temperature (MAT) gradient from -1.9 to 5.1°C in temperate mixed forest ecosystems in parallel with SOM quality and bioavailability, microbial taxonomic composition, and functional genes responsible for organic carbon decomposition. Within this temperature gradient of 7.0°C, the Q10 values increased with MAT, but decreased with SOM bioavailability. The Q10 values increased with the prevalence of K-strategy of soil microbial community, which was characterized by: (i) high ratios of oligotrophic to copiotrophic taxa, (ii) ectomycorrhizal to saprotrophic fungi, (iii) functional genes responsible for degradation of recalcitrant to that of labile C, and (iv) low average 16S rRNA operon copy number. Because the recalcitrant organic matter was mainly utilized by the K-strategists, these findings independently support the carbon quality-temperature theory from the perspective of microbial taxonomic composition and functions. A year-long incubation experiment was performed to determine the response of labile and recalcitrant C pools to warming based on the two-pool model. The decomposition of recalcitrant SOM was more sensitive to increased temperature in southern warm regions, which might attribute to the dominance of K-selected microbial communities. It implies that climate warming would mobilize the larger recalcitrant pools in warm regions, exacerbating the positive feedback between increased MAT and CO2 efflux. This is the first attempt to link temperature sensitivity of SOM decomposition with microbial eco-strategies by incorporating the genetic information and disentangling the complex relationship between Q10 and soil microorganisms.

Altered microbial structure and function after thermokarst formation.

Permafrost thaw could induce substantial carbon (C) emissions to the atmosphere, and thus trigger a positive feedback to climate warming. As the engine of biogeochemical cycling, soil microorganisms exert a critical role in mediating the direction and strength of permafrost C-climate feedback. However, our understanding about the impacts of thermokarst (abrupt permafrost thaw) on microbial structure and function remains limited. Here we employed metagenomic sequencing to analyze changes in topsoil (0-15cm) microbial communities and functional genes along a permafrost thaw sequence (1, 10, and 16years since permafrost collapse) on the Tibetan Plateau. By combining laboratory incubation and a two-pool model, we then explored changes in soil labile and stable C decomposition along the thaw sequence. Our results showed that topsoil microbial α-diversity decreased, while the community structure and functional gene abundance did not exhibit any significant change at the early stage of collapse (1year since collapse) relative to non-collapsed control. However, as the time since the collapse increased, both the topsoil microbial community structure and functional genes differed from the control. Abundances of functional genes involved in labile C degradation decreased while those for stable C degradation increased at the late stage of collapse (16years since collapse), largely driven by changes in substrate properties along the thaw sequence. Accordingly, faster stable C decomposition occurred at the late stage of collapse compared to the control, which was associated with the increase in relative abundance of functional genes for stable C degradation. These results suggest that upland thermokarst alters microbial structure and function, particularly enhances soil stable C decomposition by modulating microbial functional genes, which could reinforce a warmer climate over the decadal timescale.

Unraveling the contributions to the neuromelanin-MRI contrast

The Locus Coeruleus (LC) and the Substantia Nigra (SN) are small brainstem nuclei that change with aging and may be involved in the development of various neurodegenerative and psychiatric diseases. Magnetization Transfer (MT) MRI has been shown to facilitate LC and the SN visualization, and the observed contrast is assumed to be related to neuromelanin accumulation. Imaging these nuclei may have predictive value for the progression of various diseases, but interpretation of previous studies is hindered by the fact that the precise biological source of the contrast remains unclear, though several hypotheses have been put forward. To inform clinical studies on the possible biological interpretation of the LC- and SN contrast, we examined an agar-based phantom containing samples of natural Sepia melanin and synthetic Cys-Dopa-Melanin and compared this to the in vivo human LC and SN. T1 and T2* maps, MT spectra and relaxation times of the phantom, the LC and the SN were measured, and a two-pool MT model was fitted. Additionally, Bloch simulations and a transient MT experiment were conducted to confirm the findings. Overall, our results indicate that Neuromelanin-MRI contrast in the LC likely results from a lower macromolecular fraction, thus facilitating interpretation of results in clinical populations. We further demonstrate that in older individuals T1 lengthening occurs in the LC.