Natural Abundance 13C Research Articles

Comparison of Total Body Vitamin A Stores Using Individual versus Population 13C-Natural Abundance of Serum Retinol in Preschool Children and Women Residing in 6 Diverse African Countries

BackgroundStable isotope techniques using 13C to assess vitamin A (VA) dietary sources, absorption, and total body VA stores (TBSs) require determination of baseline 13C abundance. 13C-natural abundance is approximately 1.1% total carbon, but varies with foods consumed, supplements taken, and food fortification with synthetic retinyl palmitate. ObjectivesWe determined 13C variation from purified serum retinol and the resulting impact on TBSs using pooled data from preschool children in Burkina Faso, Cameroon, Ethiopia, South Africa, Tanzania, and Zambia and Zambian women. MethodsSeven studies included children (n = 639; 56 ± 25 mo; 48% female) and one in women (n = 138; 29 ± 8.5 y). Serum retinol 13C-natural abundance was determined using GC-C-IRMS. TBSs were available in 7 studies that employed retinol isotope dilution (RID). Serum CRP and α1-acid-glycoprotein (AGP) were available from 6 studies in children. Multivariate mixed models assessed the impact of covariates on retinol 13C. Spearman correlations and Bland–Altman analysis compared serum and milk retinol 13C and evaluated the impact of using study- or global-retinol 13C estimates on calculated TBSs. Results13C-natural abundance (%, median [Q1, Q3]) differed among countries (low: Zambia, 1.0744 [1.0736, 1.0753]; high: South Africa, 1.0773 [1.0769, 1.0779]) and was associated with TBSs, CRP, and AGP in children and with TBSs in women. 13C-enrichment from serum and milk retinol were correlated (r = 0.52; P = 0.0001). RID in children and women using study and global estimates had low mean bias (range, −3.7% to 2.2%), but larger 95% limits of agreement (range, −23% to 37%). Conclusions13C-natural abundance is different among human cohorts in Africa. Collecting this information in subgroups is recommended for surveys using RID. When TBSs are needed on individuals in clinical applications, baseline 13C measures are important and should be measured in all enrolled subjects.

One Ca2+ Site in CaNaY Zeolite Can Attach Three CO2 Molecules.

To design efficient CO2 capture materials, it is necessary to ensure a high adsorption capacity. We recently reported that one Na+ site in NaY zeolite can attach two CO2 molecules. However, the process is not suitable for practical use because it proceeds at a low temperature. Here, we present results on CO2 adsorption on CaNaY zeolites, demonstrating that one Ca2+ site can attach three CO2 molecules. The ν3(13CO2) mode arising from the natural 13C abundance allows for easy infrared monitoring of the processes: it appears at 2298, 2294, and 2291 cm-1 for the complexes with one, two, and three CO2 ligands, respectively. The 12CO2 molecules in the polyligand complexes interact vibrationally, leading to the split of the ν3(12CO2) modes. At ambient temperature, Ca2+(CO2)2 complexes predominate at >1 mbar CO2 and triligand species begin to form at 65 mbar. The obtained results show that CaY zeolites can be very effective CO2 capture materials.

Soil organic carbon transfer in aggregates subjected to afforestation in karst region as indicated by 13C natural abundance

The measurement of 13C natural abundance provides valuable information in studying carbon (C) incorporation in soil aggregates. Exploring the pathways of C between aggregates of different size classes are vital to further understand the stabilization of soil organic matter (SOM) and aggregate formation. However, little is known on the mechanism of C stabilization in soil, especially when subjected to afforestation effects in karst rocky desertification area. Soil in the 0–20 cm layer was collected from two afforestation types [natural secondary forest (NF) and artificial Zanthoxylum bungeanum forest (AF)] in the karst rocky desertification area, with cropland (CL) as the reference. Stable isotope fractionation was used to analyze the dynamic changes in organic carbon (OC) in aggregates, and the Δ13C (difference in δ13C between the bulk soil and aggregate fractions) was utilized to quantify the C flow in aggregates under different land use types and soil layers. Results showed that afforestation significantly affected the dynamics of soil aggregate OC. Afforestation on cropland increased the number of large macroaggregates (>2 mm, LMA) and decreased the proportions of small macroaggregates (0.25–2 mm, SMA), microaggregates (0.053–0.25 mm, MI), and silt + clay fraction (<0.053 mm, SC). With the increase in aggregate class size, the OC content in aggregates rose under CL and AF, but no obvious regularity was found in NF. The proportion of new SOC was higher in NF (27.0%) than in AF (20.6%) and in 0–10 cm soil layer (27.3%) than in 10–20 cm soil layer (20.3%) under different afforestation measures. No significant differences in particle size were found among aggregates (P > 0.05). The δ13C in bulk soil and aggregates was significantly decreased by afforestation and increased with the increment in soil depth. Stable isotope analysis results showed that the flow of OC was mainly from larger aggregates to smaller aggregates in CL and AF, which is consistent with the stabilization mechanism of SOM in aggregate hierarchy theory. However, the C flow occurred from smaller aggregates to larger aggregates in NF topsoil due to that newly input OC is first associated with MI and then incorporated into macroaggregates during soil aggregation process. The different human disturbance frequencies and the replenishment levels of plant biomass through litter input, root biomass, and exudates resulted in variation in aggregate turnover (formation and breakdown) among CL, AF and NF. These conclusions can provide sufficient reference for the formation and stabilization of aggregate-associated OC.

Detection of intact vancomycin-arginine as the active antibacterial conjugate in E. coli by whole-cell solid-state NMR.

The introduction of new and improved antibacterial agents based on facile synthetic modifications of existing antibiotics represents a promising strategy to deliver urgently needed antibacterial candidates to treat multi-drug resistant bacterial infections. Using this strategy, vancomycin was transformed into a highly active agent against antibiotic-resistant Gram-negative organisms in vitro and in vivo through the addition of a single arginine to yield vancomycin-arginine (V-R). Here, we report detection of the accumulation of V-R in E. coli by whole-cell solid-state NMR using 15N-labeled V-R. 15N CPMAS NMR revealed that the conjugate remained fully amidated without loss of arginine, demonstrating that intact V-R represents the active antibacterial agent. Furthermore, C{N}REDOR NMR in whole cells with all carbons at natural abundance 13C levels exhibited the sensitivity and selectivity to detect the directly bonded 13C-15N pairs of V-R within E. coli cells. Thus, we also present an effective methodology to directly detect and evaluate active drug agents and their accumulation within bacteria without the need for potentially perturbative cell lysis and analysis protocols.

Compared with Milk Protein, a Wheat and Pea Protein Blend Reduces High-Fat, High-Sucrose Induced Metabolic Dysregulations while Similarly Supporting Tissue Protein Anabolism in Rats

BackgroundPlant proteins (PPs) have been associated with better cardiovascular health than animal proteins (APs) in epidemiological studies. However, the underlying metabolic mechanisms remain mostly unknown. ObjectivesUsing a combination of cutting-edge isotopic methods, we aimed to better characterize the differences in protein and energy metabolisms induced by dietary protein sources (PP compared with AP) in a prudent or western dietary context. MethodsMale Wistar rats (n = 44, 8 wk old) were fed for 4.5 mo with isoproteic diets differing in their protein isolate sources, either AP (100% milk) or PP (50%:50% pea: wheat) and being normal (NFS) or high (HFS) in sucrose (6% or 15% kcal) and saturated fat (7% or 20% kcal), respectively. We measured body weight and composition, hepatic enzyme activities and lipid content, and plasma metabolites. In the intestine, liver, adipose tissues, and skeletal muscles, we concomitantly assessed the extent of amino acid (AA) trafficking using a 15N natural abundance method, the rates of macronutrient routing to dispensable AA using a 13C natural abundance method, and the metabolic fluxes of protein synthesis (PS) and de novo lipogenesis using a 2H labeling method. Data were analyzed using ANOVA and Mixed models. ResultsAt the whole-body level, PP limited HFS-induced insulin resistance (–27% in HOMA-IR between HFS groups, P < 0.05). In the liver, PP induced lower lipid content (–17%, P < 0.01) and de novo lipogenesis (–24%, P < 0.05). In the different tissues studied, PP induced higher AA transamination accompanied by higher routings of dietary carbohydrates and lipids toward dispensable AA synthesis by glycolysis and β-oxidation, resulting in similar tissue PS and protein mass. ConclusionsIn growing rats, compared with AP, a balanced blend of PP similarly supports protein anabolism while better limiting whole-body and tissue metabolic dysregulations through mechanisms related to their less optimal AA profile for direct channeling to PS.

Amorphous iron oxides protect aggregate-associated organic carbon from microbial utilization and decomposition evidenced from the natural abundance of 13C

Iron oxides play a critical role in promoting organic carbon sequestration through adsorption or co-precipitation. However, the effects of iron oxide types on the stabilization of aggregate-associated organic carbon are still poorly understood. We investigated the distribution of crystalline iron oxides (Fec), amorphous iron oxides (Feo), δ13C and Fe-bound OC in soil aggregate fractions of red earth (Ferrisol). The results showed that the δ13C values in microaggregate and silt+clay fractions were significantly lower than macro- and mesoaggregate (p < 0.05). The contents of Feo and Fe-bound OC in the microaggregate and silt+clay fractions were significantly higher than macro- and masoaggregate fractions (p < 0.05), while the content of Fec increased with the increase of aggregate size. The OC: Fe molar ratio of Feo was higher than Fec in all aggregate fractions. The FTIR spectroscopy analyses showed that polysaccharides had the highest proportion of all OC functional groups and increased with the increase of aggregate size. Likewise, the ratio of aromatic-C/aliphatic-C increased with the increase of aggregate size. Both Feo and Fe-bound OC had a significant negative correlation with δ13C values in microaggregate and silt+clay fractions, while Fec had no significant correlation with δ13C values in all aggregate fractions. Furthermore, the Fe-bound OC and fFe-bound OC were positively correlated with Feo and negatively correlated with Fec in all aggregate fractions. This study highlighted the importance of Feo in the sequestration of aggregate-associated organic carbon and confirmed the hypothesis that the SOC in microaggregates and silt+clay underwent less cycles of microbial utilization due to the protection of Feo, thereby limiting the molecular structure complexity and aromaticity of SOM.

Natural 13C Abundance of Organic-Matter Pools in Haplic Chernozem

Natural 13C Abundance of Organic-Matter Pools in Haplic Chernozem

Soil microbial community structure dynamics shape the rhizosphere priming effect patterns in the paddy soil

Microbial community structure plays a crucial part in soil organic carbon (SOC) decomposition and variation of rhizosphere priming effects (RPEs) during plant growth. However, it is still uncertain how bacterial community structure regulates RPEs in soil and how RPE patterns respond to plant growth. Therefore, we conducted an experiment to examine the RPE response to plant growth and nitrogen (N) addition (0 (N0), 150 (N150), and 300 (N300) kg N ha−1) using the 13C natural abundance method in a C3 soil (paddy soil) - C4 plant (maize, Zea mays L.) system; we then explored the underlying biotic mechanisms using 16S rRNA sequencing techniques. Networks were constructed to identify keystone taxa and to analyze the correlations between network functional modules of bacterial community and C decomposition. The results indicated that negative and positive RPEs occurred on Day 30 and Day 75 after maize planting, respectively. Bacterial community structure significantly changed and tended to shift from r-strategists toward K-strategists with changing labile C: N stoichiometry and soil pH during plant growth stages. The different network modules of bacterial community were aggregated in response to RPE pattern variation. Caulobacteraceae, Bacillus, and Chitinophagaceae were keystone taxa on Day 30, while Gemmatimonas, Candidatus Koribacter, and Xanthobacteraceae were keystone taxa on Day 75. Moreover, keystone taxa with different C utilization strategies were significantly different between the two growth stages and related closely to different RPE patterns. This study provides deeper insights into the network structure of bacterial communities corresponding to RPE patterns and emphasizes the significance of keystone taxa in RPE variation.

Fine optimization of a dissolution dynamic nuclear polarization experimental setting for 13C NMR of metabolic samples.

NMR-based analysis of metabolite mixtures provides crucial information on biological systems but mostly relies on 1D H experiments for maximizing sensitivity. However, strong peak overlap of H spectra often is a limitation for the analysis of inherently complex biological mixtures. Dissolution dynamic nuclear polarization (d-DNP) improves NMR sensitivity by several orders of magnitude, which enables C NMR-based analysis of metabolites at natural abundance. We have recently demonstrated the successful introduction of d-DNP into a full untargeted metabolomics workflow applied to the study of plant metabolism. Here we describe the systematic optimization of d-DNP experimental settings for experiments at natural C abundance and show how the resolution, sensitivity, and ultimately the number of detectable signals improve as a result. We have systematically optimized the parameters involved (in a semi-automated prototype d-DNP system, from sample preparation to signal detection, aiming at providing an optimization guide for potential users of such a system, who may not be experts in instrumental development). The optimization procedure makes it possible to detect previously inaccessible protonated C signals of metabolites at natural abundance with at least 4times improved line shape and a high repeatability compared to a previously reported d-DNP-enhanced untargeted metabolomic study. This extends the application scope of hyperpolarized C NMR at natural abundance and paves the way to a more general use of DNP-hyperpolarized NMR in metabolomics studies.

Rapid 13C Hyperpolarization of the TCA Cycle Intermediate α-Ketoglutarate via SABRE-SHEATH.

α-Ketoglutarate is a key biomolecule involved in a number of metabolic pathways─most notably the TCA cycle. Abnormal α-ketoglutarate metabolism has also been linked with cancer. Here, isotopic labeling was employed to synthesize [1-13C,5-12C,D4]α-ketoglutarate with the future goal of utilizing its [1-13C]-hyperpolarized state for real-time metabolic imaging of α-ketoglutarate analytes and its downstream metabolites in vivo. The signal amplification by reversible exchange in shield enables alignment transfer to heteronuclei (SABRE-SHEATH) hyperpolarization technique was used to create 9.7% [1-13C] polarization in 1 minute in this isotopologue. The efficient 13C hyperpolarization, which utilizes parahydrogen as the source of nuclear spin order, is also supported by favorable relaxation dynamics at 0.4 μT field (the optimal polarization transfer field): the exponential 13C polarization buildup constant Tb is 11.0 ± 0.4 s whereas the 13C polarization decay constant T1 is 18.5 ± 0.7 s. An even higher 13C polarization value of 17.3% was achieved using natural-abundance α-ketoglutarate disodium salt, with overall similar relaxation dynamics at 0.4 μT field, indicating that substrate deuteration leads only to a slight increase (∼1.2-fold) in the relaxation rates for 13C nuclei separated by three chemical bonds. Instead, the gain in polarization (natural abundance versus [1-13C]-labeled) is rationalized through the smaller heat capacity of the "spin bath" comprising available 13C spins that must be hyperpolarized by the same number of parahydrogen present in each sample, in line with previous 15N SABRE-SHEATH studies. Remarkably, the C-2 carbon was not hyperpolarized in both α-ketoglutarate isotopologues studied; this observation is in sharp contrast with previously reported SABRE-SHEATH pyruvate studies, indicating that the catalyst-binding dynamics of C-2 in α-ketoglutarate differ from that in pyruvate. We also demonstrate that 13C spectroscopic characterization of α-ketoglutarate and pyruvate analytes can be performed at natural 13C abundance with an estimated detection limit of 80 micromolar concentration × *%P13C. All in all, the fundamental studies reported here enable a wide range of research communities with a new hyperpolarized contrast agent potentially useful for metabolic imaging of brain function, cancer, and other metabolically challenging diseases.

Optimization of the LLNL/CAMS gas-accepting ion source and 1 MV compact AMS for natural abundance radiocarbon analysis of CO2

The Lawrence Livermore National Laboratory – Center for Accelerator Mass Spectrometry (LLNL/CAMS) 1 MV AMS system was converted from a biomedical AMS instrument to a natural abundance 14C spectrometer. The system is equipped with a gas-accepting hybrid ion source capable of measuring both solid (graphite) and gaseous (CO2) samples. Here we describe a series of experiments intended to establish and optimize 14CO2 measurement capabilities at natural abundance levels. A maximum instantaneous ionization efficiency of 8 % was achieved with 3 % CO2 in helium at a flow rate of approximately 220 µL/min (3.5 µg C/min). For modern materials (e.g., OX I) we measured an average of 240 ± 50 14C counts/µg C, equivalent to a total system efficiency of approximately 3 %. Experimental CO2 samples with F14C values ranging from 0.20 to 1.05 measured as both graphite and directly as CO2 gas produced equivalent values with an average offset of < 2σ.

Geomorphically mediated carbon dynamics of floodplain soils and implications for net effect of carbon erosion

AbstractThe fate of organic carbon deposited in floodplain sediments is an important control on the magnitude and direction of the carbon flux from anthropogenically accelerated erosion and channelization of the riverine network. Globally, carbon deposition rates and mean residence time (MRT) within different geomorphic settings remains poorly constrained. We sampled soil profiles to 0.8 m depth from two geomorphic zones: active channel belt (ACB) and lowland floodplain, under long‐term pasture adjacent to the river Culm in SW England, UK. We evaluated sedimentation rates and carbon storage using fallout radionuclide 137Cs, particle size and total carbon analyses. Variation in decomposition was assessed via empirical (soil aggregate size, density fractionation combined with natural abundance 13C analysis) and modelling simulation (using the RothC model and catchment implications explored using a floodplain evolution model). Sedimentation and carbon accumulation rates were 5–6 times greater in the ACB than the floodplain. Carbon decomposition rates also varied with geomorphic setting. In floodplain cores, faster decomposition rates were indicated by greater 13C‐enrichment and subsoils dominated by mineral‐associated soil organic carbon. Whereas, in the ACB, carbon was less processed and 13C‐depleted, with light fraction and macroaggregate‐carbon throughout the cores, and RothC modelled decomposition rates were 4‐fold less than lowland floodplain cores. Including the ACB in floodplain carbon MRT calculations increased overall MRT by 10%. The major differences in the balance of sedimentation and decomposition rates between active and inactive floodplains suggests the relative extent of these contrasting zones is critical to the overall carbon balance. Restoration projects could enhance soil carbon storage by maximizing active floodplain areas by increasing river channel complexity.

Divergent carbon stabilization pathways in aggregates in Ultisols with and without organic amendments: Implications from 13C natural abundance and NMR analysis

Ultisols with high physio-chemical protection and high acidity prevent soil organic carbon (SOC) from microbial decomposition and accumulate plant-derived recalcitrant C by forming organo-metal complexes. Therefore, the C stabilization pathways in Ultisols may challenge the current common understanding, which is that the major pathway is the stabilization of microbial-derived C to minerals. In addition, organic amendments are expected to affect C stabilization pathways by promoting SOC decomposition and changing SOC composition. However, limited evidence has been found for Ultisols, and the underlying mechanism remains under discussion. C stabilization processes lead to 13C fractionation and changes in SOC composition among aggregate fractions. Therefore, 13C natural abundance and 13C nuclear magnetic resonance spectrometry approaches were applied to investigate 13C fractionation and SOC composition, especially the relative content of recalcitrant C, such as lignin and lipids, and the humification degree represented by the O-alkyl/alkyl ratio, between aggregate size classes. Five fertilization regimes from an 8-year field experiment were selected: no fertilization (CK), inorganic fertilizer (NPK), NPK + straw (NS), NPK + straw and manure (NSM), and NPK + biochar (NC). The bulk soil was separated into three aggregate fractions: >2000 μm, 250–2000 μm, and < 250 μm. In all treatments, 13C presented greater depletion in microaggregates (<250 μm) than macroaggregates (>2000 μm and 250–2000 μm). Regarding the changes in SOC composition, in non-organic-amended treatments (CK and NPK) and NC, recalcitrant C fractions, such as lignin and lipids, were more abundant in < 250 μm aggregates. With the fresh organic material (OM) application (NS and NSM), the lowest O-alkyl/alkyl ratio was found in the > 2000 μm aggregates, suggesting a high humification degree. Summarizing the δ13C and SOC composition results, in the non-organic-amended treatments and NC, the depletion of δ13C in microaggregates coincided with the enrichment of recalcitrant C, which suggests that the depletion of δ13C was primarily controlled by the preferential substrate utilization mechanism. Thus, labile C with heavier δ13C is preferentially decomposed while partially oxidized recalcitrant C with lighter δ13C was adsorbed to the mineral surface and protected in microaggregates. Because the δ13C value decreases with the aggregate size, C flow (modeled in a scheme) primarily occurred from macroaggregates to microaggregates. With fresh OM input (NS and NSM), the C stabilization pathway was primarily governed by the kinetic fractionation mechanism; that is, heavier δ13C remained after microbial utilization, which was reflected by the association of heavier δ13C and a lower O-alkyl/alkyl ratio. With macroaggregates exhibiting 13C enrichment, the C flow was primarily from microaggregates to macroaggregates. These results highlight the importance of the accumulation and protection of plant-derived recalcitrant C in microaggregates in the C stabilization pathway of Ultisols and emphasize that the C stabilizing mechanisms largely depend on organic amendments.

Carbon assimilation and water-use efficiency in cowpea varieties inoculated with Bradyrhizobium, measured using 13C natural abundance

ABSTRACT Moisture stress is one of the most important constraints for crop production in arid regions. Cowpea is a vital food legume that has been cultivated in tropical and sub-tropical regions where water is scarce. Rhizobia inoculation confers resistance to water stress legumes. Two-year field experiments were conducted to assess the carbon assimilation and water use efficiencies of inoculated cowpea varieties at three sites. The treatments consist of four varieties and three levels of Bradyrhizobium inoculation arranged in a factorial randomized complete block design with four replications. The nitrogen (% N) and carbon (% C) concentrations in plant shoots were obtained directly from the mass spectrometric analysis. The results revealed considerable variation for shoot % N and % C, shoot growth, and δ13C among the varieties. Similarly, Bradyrhizobium significantly affected plant growth, % C, C and N contents, C/N ratio, and carbon isotope discrimination of the shoot. For instance, C and N contents and the C/N ratio increased by 28, 24, and 31%, respectively, due to Bradyrhizobium inoculation. In general, these results indicated that physiological performances such as carbon assimilation and water use efficiency of the crop could be, significantly improved when effective Bradyrhizobium strains and the best performing varieties are selected.

Detection of natural abundance 13C J-couplings at Earth’s magnetic field for spin system differentiation of small organic molecules

Nuclear magnetic resonance (NMR) spectroscopy routinely characterizes the unique spin systems of molecules using a combination of chemical shift and J-coupling interactions for the 1H and 13C nuclei. However, at Earth’s magnetic field, chemical shifts are unresolvable and the ability to characterize structure relies solely on the J-couplings. Fortuitously, the J-couplings at Earth’s field provides the same spin system information as high field, but only requires detection of the 1H nucleus. We report the first identification of the multiple natural abundance 1H–13C spin systems on organic molecules detected at Earth’s magnetic field. The results clearly demonstrate the feasibility of Earth’s field NMR to characterize small organic molecules without costly enrichment strategies.

Multiple Dynamic Nuclear Polarization Mechanisms in Carbonaceous Materials: From Exogenous to Endogenous 13C Dynamic Nuclear Polarization-Nuclear Magnetic Resonance up to Room Temperature

Carbonaceous materials are ubiquitous in energy storage and conversion systems due to their versatile chemical and physical properties. The surface chemistry of carbonaceous materials strongly affects their properties, and there is therefore great interest in determining the chemical composition of different carbon allotropes. Solid-state nuclear magnetic resonance spectroscopy is well suited for providing atomic-level structural information, especially when equipped with sensitivity from dynamic nuclear polarization (DNP). Exogenous DNP from nitroxide biradicals is the most efficient approach, typically providing 102–104 fold enhancement in surface sensitivity. Herein, we consider the application of DNP in the study of the surface chemistry of carbonaceous materials through natural abundance 13C detection. We found that with TEKPol biradicals, the polarization transfer via 1H-13C cross-polarization is limited to the solvent and does not propagate to the sample surface. We thus investigated in detail polarization transfer directly to 13C nuclei and found multiple interfering mechanisms when employing the exogenous DNP approach: (a) direct 13C polarization from the biradicals, (b) opposite enhancements due to heteronuclear cross-relaxation leading to the solvent Overhauser effect, and (c) solid effect from defects and delocalized electrons within the carbons. While the endogenous electron polarization interferes with the utilization of exogenous DNP, it provides significant surface sensitivity with signal enhancements of up to 50 and 20 for 13C and 1H, respectively. Moreover, we show that endogenous DNP can be used at a wide range of temperatures, providing close to a 10-fold increase in 13C and 1H signals at room temperature through differing DNP mechanisms. This approach opens the way for efficient detection of carbon surface chemistry under ambient conditions.

Examining the contributions of maize shoots, roots, and manure to stable soil organic carbon pools in tropical smallholder farming soils

Continuous inputs of organic matter are vital for sustaining soil organic carbon (SOC) and productivity of soils in smallholder crop-livestock systems. However, the dynamics of the different inputs i.e. maize shoots, roots and manure used are poorly understood. Along with organic inputs, use of mineral fertilizers can alter the nutrient stoichiometry of organic matter inputs and have implications for SOC turnover. This study sought to understand how maize-based inputs and alterations to nutrient stoichiometry contribute to stable SOC pools. We hypothesized that higher quality litter (i.e., manure) contributes more than maize residues to stable SOC pools and that N, P and S additions, designed to balance the stoichiometry of inputs to reflect the stable fine fraction of soil organic matter (C:N:P:S-10,000:833:200:143) results in greater SOC stabilization. We used a 13C natural abundance approach, where the C4 maize residues were incubated for 11 months to trace C stabilization into different SOC pools within a C3 soil. Contrary to our expectations, we observed greater recovery and stabilization of shoot-derived C (2 X more than manure and 1.63 X more than roots) in the mineral-associated organic matter (MAOM) fraction. Mineral N, P and S additions reduced new C recovery in MAOM by 40 % compared to no mineral nutrient’s additions. Our study highlights the importance of residue retention as a strategy to maintain SOC and soil health in smallholder systems, and our results challenge the idea that nutrient additions increase C stabilization of added residues.

Variations in the chemical structure and Carbon-13 natural abundance in water-stable macro- and microaggregates in Haplic Chernozem under the contrasting land use variants

Water-stable macro- (WSAma) and free microaggregates (WSAmi) were isolated from the 2-1mm air-dry macroaggregates from the surface horizons of Haplic Chernozem in contrasting variants of land use: the steppe and the bare fallow. The 13C NMR data and the 13C natural abundance of the Occluded organic matter (OM) (LFoc) and Clay within WSAs in the steppe obviously indicate a lower degree of microbiological processing of OM within WSAmi as compared with WSAma. This is reflected in lower degrees of decomposition (DI) and aromaticity (ARI) of OM and the C/N ratio, as well as lower 13C enrichment. This implies that the "labile" part of OM within WSAmi (LFoc and Clay, which are components of microaggregates within water-stable aggregates (mWSAs)) is more physically protected compared to that within WSAma. However, the heavier total δ13C signature of OM within WSAmi indicates its greater degree of microbiological processing compared to that within WSAma. This seems contrary to the concept of greater physical protection of OM within microaggregates as compared to macroaggregates. It was revealed that the heavier total δ13C signature of OM within WSAmi (greater degree of microbiological processing) is determined by the "oldest" OM located in the inter-aggregate space of WSAs, which is concentrated in the Residue fraction (Res). Due to its quantitative dominance, the Residue fraction is crucial for the total δ13C signature of WSAs. Negative changes in the quality of OM under the long-term bare fallow (52-yr) were reflected in a sharp increase in the integral indices of the chemical structure (DI, ARI), as well as the hydrophobicity index (HI) in all studied OM pools. It was accompanied by their 13C enrichment in the bare fallow compared to the steppe. Free microaggregates (WSAmi) are fragments of disintegrated macroaggregates (WSAma). We found no evidence of their formation within macroaggregates.

13C Natural Isotope Abundance in Urothelium as a New Marker in the Follow-Up of Patients with Bladder Cancer.

Simple SummaryBladder cancer (BC) is a common urological cancer and has a high incidence of recurrence. Metabolic changes are one of the hallmarks of cancer. Differences in metabolic pathways between normal and cancerous tissues lead to a heterogeneous distribution of natural isotope abundance. We analyzed the isotope ratio of carbon, nitrogen, and sulfur in normal urothelium and bladder cancer samples and correlated these data with clinical parameters. We found that bladder cancers are 13C- and 15N-depleted when compared to normal urothelium. Furthermore, decreased 13C abundance in normal urothelium is correlated with shorter disease-free survival in bladder cancer patients. Determination of the isotopic signature of normal and cancerous bladder biopsies can provide important information about the risk of recurrence and improve patients’ management by avoiding invasiveness and unnecessary diagnostic procedures such as cystoscopy.Bladder cancer (BC) is the most common urological malignancy and has a high incidence of recurrence. BC cells alter their nutrient uptake and metabolic pathways in order to continue the production of sufficient levels of ATP and metabolic intermediates for proliferation and survival. Changes in metabolic pathways regarding the rate of the enzymatic reaction and transport lead to differences in the content of natural isotopes (13C, 15N, 34S) between normal and cancerous tissues. The assessment of the stable isotopes of carbon, nitrogen, and sulfur in normal urothelium and bladder cancer samples was performed using Isotope Ratio Mass Spectrometry (IRMS). The natural abundance of 15N and 13C was decreased in bladder cancer samples when compared to normal urothelium. No significant correlation was observed in BC specimens depending on the tumor grade and stage. Samples derived from bladder tumors and normal urothelium had a different pattern of 15N and 13C isotope abundance. Decreased 13C natural isotopes in the normal urothelium of BC patients were significantly associated with a shorter DFS. Our results suggest that isotopic analysis of normal urothelium of BC patients can be used to predict bladder cancer recurrence.

Grain carbon isotope composition is a marker for allocation and harvest index in wheat.

The natural 13C abundance (δ13C) in plant leaves has been used for decades with great success in agronomy to monitor water‐use efficiency and select modern cultivars adapted to dry conditions. However, in wheat, it is also important to find genotypes with high carbon allocation to spikes and grains, and thus with a high harvest index (HI) and/or low carbon losses via respiration. Finding isotope‐based markers of carbon partitioning to grains would be extremely useful since isotope analyses are inexpensive and can be performed routinely at high throughput. Here, we took the advantage of a set of field trials made of more than 600 plots with several wheat cultivars and measured agronomic parameters as well as δ13C values in leaves and grains. We find a linear relationship between the apparent isotope discrimination between leaves and grain (denoted as Δδcorr), and the respiration use efficiency‐to‐HI ratio. It means that overall, efficient carbon allocation to grains is associated with a small isotopic difference between leaves and grains. This effect is explained by postphotosynthetic isotope fractionations, and we show that this can be modelled by equations describing the carbon isotope composition in grains along the wheat growth cycle. Our results show that 13C natural abundance in grains could be useful to find genotypes with better carbon allocation properties and assist current wheat breeding technologies.