Natural Abundance Carbon Research Articles

Abstract IA14: Host autophagy mediates organ wasting and nutrient mobilization for tumor growth

Abstract During tumor growth-when nutrient and anabolic demands are high-autophagy supports tumor metabolism and growth through lysosomal organelle turnover and nutrient recycling. Ras-driven tumors additionally invoke non-autonomous autophagy in the microenvironment to support tumor growth, in part through transfer of amino acids. Here we uncover a third critical role of autophagy in mediating systemic organ wasting and nutrient mobilization for tumor growth using a well-characterized malignant tumor model in Drosophila melanogaster. Micro-computed X-ray tomography and metabolic profiling reveal that RasV12 ; scrib-/- tumors grow 10-fold in volume, while systemic organ wasting unfolds with progressive muscle atrophy, loss of body mass, -motility, -feeding, and eventually death. Tissue wasting is found to be mediated by autophagy and results in host mobilization of amino acids and sugars into circulation. Natural abundance Carbon 13 tracing demonstrates that tumor biomass is increasingly derived from host tissues as a nutrient source as wasting progresses. Thus, host autophagy mediates organ wasting and nutrient mobilization that is utilized for tumor growth. Citation Format: Petter Holland, Todd Andrew Schoborg, Ifat Abramovich, Szabolcs Takáts, Caroline Dillard, Ashish Jain, Fergal O'Farrell, Sebastian Wolfgang Schultz, William M. Hagopian, Eduardo Martin Quintana, Rachel Ng, Nadja Sandra Katheder, Mohammed Mahidur Rahman, José Gerardo Teles Reis, Andreas Brech, Heinrich Jasper, Nasser M. Rusan, Anne Hope Jahren, Eyal Gottlieb, Tor Erik Rusten. Host autophagy mediates organ wasting and nutrient mobilization for tumor growth [abstract]. In: Proceedings of the AACR Special Conference: Targeting RAS; 2023 Mar 5-8; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Res 2023;21(5_Suppl):Abstract nr IA14.

Mass Spectrometry Insight for Assessing the Destiny of Plastics in Seawater

Plastic pollution has become an increasingly serious environmental issue that requires using reliable analytical tools to unravel the transformations of primary plastics exposed to the marine environment. Here, we evaluated the performance of the isotope ratio mass spectrometry (IRMS) technique for identifying the origin of polymer material contaminating seawater and monitoring the compositional alterations due to its chemical degradation. Of twenty-six plastic specimens available as consumer products or collected from the Mediterranean Sea, five plastics were shown to originate from biobased polymeric materials. Natural abundance carbon and hydrogen isotope measurements revealed that biopolymers incline to substantial chemical transformation upon a prolonged exposure to seawater and sunlight irradiation. To assess the seawater-mediated aging that leads to the release of micro/nano fragments from plastic products, we propose to use microfiltration. Using this non-destructive separation technique as a front end to IRMS, the fragmentation of plastics (at the level of up to 0.5% of the total mass for plant-derived polymers) was recorded after a 3-month exposure and the rate and extent of disintegration were found to be substantially different for the different classes of polymers. Another potential impact of plastics on the environment is that toxic metals are adsorbed on their surface from the seashore water. We addressed this issue by using inductively coupled mass spectrometry after nitric acid leaching and found that several metals occur in the range of 0.1-90 µg per g on naturally aged plastics and accumulate at even higher levels (up to 10 mg g-1) on pristine plastics laboratory-aged in contaminated seawater. This study measured the degradation degree of different polymer types in seawater, filling in the gaps in our knowledge about plastic pollution and providing a useful methodology and important reference data for future research.

Quantitative and carbon isotope ratio analysis of fatty acids isolated from human brain hemispheres.

Our knowledge surrounding the overall fatty acid profile of the adult human brain has been largely limited to extrapolations from brain regions in which the distribution of fatty acids varies. This is especially problematic when modeling brain fatty acid metabolism, therefore, an updated estimate of whole-brain fatty acid concentration is necessitated. Here, we sought to conduct a comprehensive quantitative analysis of fatty acids from entire well-characterized human brain hemispheres (n= 6) provided by the Douglas-Bell Canada Brain Bank. Additionally, exploratory natural abundance carbon isotope ratio (CIR; δ13 C, 13 C/12 C) analysis was performed to assess the origin of brain fatty acids. Brain fatty acid methyl esters (FAMEs) were quantified by gas chromatography (GC)-flame ionization detection and minor n-6 and n-3 polyunsaturated fatty acid pentafluorobenzyl esters by GC-mass spectrometry. Carbon isotope ratio values of identifiable FAMEs were measured by GC-combustion-isotope ratio mass spectrometry. Overall, the most abundant fatty acid in the human brain was oleic acid, followed by stearic acid (STA), palmitic acid (PAM), docosahexaenoic acid (DHA), and arachidonic acid (ARA). Interestingly, cholesterol as well as saturates including PAM and STA were most enriched in 13 C, while PUFAs including DHA and ARA were most depleted in 13 C. These findings suggest a contribution of endogenous synthesis utilizing dietary sugar substrates rich in 13 C, and a combination of marine, animal, and terrestrial PUFA sources more depleted in 13 C, respectively. These results provide novel insights on cerebral fatty acid origin and concentration, the latter serving as a valuable resource for future modeling of fatty acid metabolism in the human brain.

Synergy between Sunlight, Titanium Dioxide, and Microbes Enhances Cellulose Diacetate Degradation in the Ocean.

Sunlight chemically transforms marine plastics into a suite of products, with formulation—the specific mixture of polymers and additives—driving rates and products. However, the effect of light-driven transformations on subsequent microbial lability is poorly understood. Here, we examined the interplay between photochemical and biological degradation of fabrics made from cellulose diacetate (CDA), a biobased polymer used commonly in consumer products. We also examined the influence of ∼1% titanium dioxide (TiO2), a common pigment and photocatalyst. We sequentially exposed CDA to simulated sunlight and native marine microbes to understand how photodegradation influences metabolic rates and pathways. Nuclear magnetic resonance spectroscopy revealed that sunlight initiated chain scission reactions, reducing CDA’s average molecular weight. Natural abundance carbon isotope measurements demonstrated that chain scission ultimately yields CO2, a newly identified abiotic loss term of CDA in the environment. Measurements of fabric mass loss and enzymatic activities in seawater implied that photodegradation enhanced biodegradation by performing steps typically facilitated by cellulase. TiO2 accelerated CDA photodegradation, expediting biodegradation. Collectively, these findings (i) underline the importance of formulation in plastic’s environmental fate and (ii) suggest that overlooking synergy between photochemical and biological degradation may lead to overestimates of marine plastic persistence.

An evaluation of the serum carbon isotope ratio as a candidate predictive biomarker of the dietary animal protein ratio (animal protein/total protein) in a 15-day controlled feeding study of US adults

The serum natural abundance carbon isotope ratio (CIR) was recently identified as a candidate biomarker of animal protein intake in postmenopausal women. Such a biomarker would help clarify the relation between dietary protein source (plant or animal) and chronic disease risk. We aimed to evaluate the performance of the serum CIR as a biomarker of dietary protein source in a controlled feeding study of men and women of diverse age and BMI. We conducted a 15-d feeding study of 100 adults (age: 18-70 y, 55% women) in Phoenix, AZ. Participants were provided individualized diets that approximated habitual food intakes. Serum was collected at the end of the feeding period for biomarker measurements. Median [IQR] animal protein intake was 67 g/d [55-88 g/d], which was 64% of total protein. The serum CIR was positively correlated with animal protein and inversely correlated with plant protein intake, leading to a strong correlation (r2=0.76) with the dietary animal protein ratio (APR; animal/total protein). Regressing serum CIR on the APR, serum nitrogen isotope ratio (NIR), gender, age, and body weight generated an R2 of 0.78. Following the measurement error model for predictive biomarkers, the resulting regression equation was then inverted to develop a calibrated biomarker equation for APR. Added sugars ratio (added/total sugars intake) and corn intakes also influenced the serum CIR but to a much lesser degree than the APR; variations in these intakes had only small effects on biomarker-estimated APR. Based on our findings in this US cohort of mixed sex and age, we propose the serum CIR alongside NIR as a predictive dietary biomarker of the APR. We anticipate using this biomarker to generate calibrated estimates based on self-reported intake and ultimately to obtain more precise disease risk estimates according to dietary protein source.

Host autophagy mediates organ wasting and nutrient mobilization for tumor growth

During tumor growth—when nutrient and anabolic demands are high—autophagy supports tumor metabolism and growth through lysosomal organelle turnover and nutrient recycling. Ras‐driven tumors additionally invoke non‐autonomous autophagy in the microenvironment to support tumor growth, in part through transfer of amino acids. Here we uncover a third critical role of autophagy in mediating systemic organ wasting and nutrient mobilization for tumor growth using a well‐characterized malignant tumor model in Drosophila melanogaster. Micro‐computed X‐ray tomography and metabolic profiling reveal that RasV12; scrib−/− tumors grow 10‐fold in volume, while systemic organ wasting unfolds with progressive muscle atrophy, loss of body mass, ‐motility, ‐feeding, and eventually death. Tissue wasting is found to be mediated by autophagy and results in host mobilization of amino acids and sugars into circulation. Natural abundance Carbon 13 tracing demonstrates that tumor biomass is increasingly derived from host tissues as a nutrient source as wasting progresses. We conclude that host autophagy mediates organ wasting and nutrient mobilization that is utilized for tumor growth.

Evaluating the Serum Carbon Isotope Ratio as a Biomarker for Animal Protein Ratio in a Controlled Feeding Study of US Adults

ObjectivesRecent studies have identified the serum natural abundance carbon isotope ratio (CIR) as a candidate biomarker of animal protein intake in postmenopausal women. Such a biomarker would help clarify the contribution of dietary protein source (animal vs. vegetable) to chronic disease risk. Here we evaluate biomarker performance and develop a biomarker calibration equation in a mixed-age and – gender cohort. MethodsWe conducted a 15-d feeding study of 100 adults (age 18–70, 55% women) in Phoenix, AZ. Participants were provided individualized diets that approximated habitual food intakes. Total CIR and nitrogen isotope ratio (NIR) were measured in sera collected at the end of the feeding period. We expressed animal protein as a ratio of total protein intake (APratio). We evaluated a model of serum CIR based on APratio, the serum NIR, gender, age and body weight, and the resulting regression equation was inverted to develop an equation for the APratio that we call the calibrated biomarker. We evaluated the association of the calibrated biomarker with actual APratio using Pearson correlation and 5-fold cross validation. ResultsAnimal protein intake in this study was 73 ± 30 g/d (mean ± SD) and the APratio was 0.63 ± 0.13. Our model explained a large proportion of the variation in serum CIR (R2 = 0.77) and APratio was the only significant model effect (coefficient = 6.22, SE = 0.44, P < 0.0001). Inverting that model generated the following biomarker calibration equation: APratio = (CIR – 26.35 – 0.06 (gender) + 0.068 * In age – 0.215 * In body weight – 0.204 * serum NIR)/6.22, where gender = 1,0 (male, female). There was a strong correlation between model-predicted and actual APratio (rP = 0.85, P < 0.0001), with the mean model-predicted APratio differing from mean actual APratio by 0.0015 (SE = 0.0077). The standard deviation of the prediction error was 0.076. The 5-fold cross validation procedure produced very similar model R2, effects, and prediction errors. ConclusionsThese data suggest that the serum CIR has potential as a predictive biomarker of APratio, providing a useful tool for objectively assessing dietary protein intake patterns. Such a tool could help resolve the contribution of dietary patterns favoring animal protein intake to chronic disease risk. Funding SourcesThis work was funded by NIH U01 CA197902.

Carbon and Nitrogen Sourcing in High Elevation Landscapes of Mustang in Central Nepal

Mustang valley in the central Himalaya of Nepal is a unique landscape formed by massive soil mass during a glacial period, which is attributed to a mix of vegetations and long agricultural history. Soil nutrients and their sourcing is highly important to understand the vegetation assemblage and land productivity in this arid zone. Twenty soil samples (from 0 to 20 cm depth) were collected from three landscape positions in Mustang district: valley, ridge, and midslope. We explored nutrient sourcing using natural abundance carbon (δ13C) and nitrogen isotope (δ15N) employing isotope ratio mass spectrophotometry. The results showed that the total soil carbon (TC) and total nitrogen (TN) ranged from 0.3 to 10.5% and 0.3 to 0.7%, respectively. Similarly, the CN ratio ranged from 0.75 to 15.6, whereas soil pH ranged from 6.5 to 7.5. Valley soil showed higher values of TN, CN, and soil pH than the ridge and midslope soils. The valleys had more positive δ15N signatures than ridge and midslope, which indicates higher inorganic and organic N fertilizer inputs in the valley bottom than in the midslope and ridge. This suggests that a higher nutrient content in the valley bottom likely results from agro-inputs management and the transport of nutrients from the ridge and midslope. Soil pH and CN ratio were a non-limiting factor of nutrient availability in the study regions. These findings are crucial in understanding the nutrient dynamics and management in relation to vegetation and agricultural farming in this unique topography of the Trans-Himalayan zone of Mustang in central Nepal.

Natural abundance carbon isotope ratio analysis and its application in the study of diet and metabolism.

Due to differences in carbon assimilation pathways between plants, there are subtle but distinct variations in the carbon isotope ratios of foods and animal products throughout the food supply. Although it is well understood that the carbon isotope ratio composition of the diet influences that of the consumers' tissues, the application of natural abundance carbon isotope ratio analysis in nutrition has long been underappreciated. Over the past decade, however, several studies have investigated the utility of carbon isotope ratio analysis for evaluation of nutritional biomarker status, primarily focusing on its application as an objective indicator of sugar and animal protein intake. More recently, research investigating the application of natural abundance measurements has been extended to study fatty acid metabolism and has yielded encouraging results. Collectively, data from large-scale observational studies and experimental animal studies highlight the potential for carbon isotope ratio analysis as an additional and effective tool to study diet and metabolism. The purpose of this review is to provide an overview of natural abundance carbon isotope ratio analysis, its application to studying nutrition, and an update of the research in the field.

Stable Carbon Isotope Studies of CH4 Dynamics Via Water and Plant Pathways in a Tropical Thai Paddy: Insights Into Diel CH4 Transportation

AbstractSeparate evaluation of methane (CH4) emission dynamics (e.g., oxidation, production, and transportation) at the soil‐plant‐atmosphere and soil‐water‐atmosphere interfaces has been limited in tropical rice paddies, but it is crucial for comprehending the entire CH4 cycles. We investigated CH4 oxidation, production, and transportation through plant and water pathways during the reproductive stage in a tropical Thailand rice paddy field using natural abundance carbon stable isotope ratios (δ13CH4 and δ13CO2). Mass balance equations using δ13CH4 and δ13CO2 in soil gases indicated that CH4 oxidation in the planted soil exceeded those in the interrow soil due to oxygen supply through rice roots. In addition, at 1–11 cm depth acetate fermentation was the dominant process in the planted soil, whereas in the interrow soil the dominant process was H2/CO2 reduction. The water pathway showed a significant negative correlation between CH4 flux and released δ13CH4 over 24 hr, driven by a diel change in episodic ebullition, steady ebullition, and diffusion, all due to diel changes in soil temperature and atmospheric pressure. In contrast, the plant pathway showed a significant positive relationship between CH4 flux and emitted δ13CH4 throughout one day. A comparison of the diel change in emitted δ13CH4 between the water and plant pathways showed that the rice plants transported CH4 in soil bubbles without any large isotopic fractionation. The diel change in the plant‐mediated CH4 transportation was mainly controlled by diel changes in soil bubble expansion and CH4 diffusion through plants, which were probably regulated by diel changes in soil temperature and atmospheric pressure.

Turnover of brain DHA in mice is accurately determined by tracer-free natural abundance carbon isotope ratio analysis

The brain is highly enriched in the long-chain omega-3 (n-3) PUFA DHA. Due to the limited capacity for local DHA synthesis in the brain, it relies on a continual supply from the circulation to replenish metabolized DHA. Previous studies investigating brain DHA turnover and metabolism have relied on isotope tracers to determine brain fatty acid kinetics; however, this approach is cumbersome and costly. We applied natural abundance carbon isotope ratio analysis via high-precision gas chromatography combustion isotope ratio mass spectrometry, without the use of labeled tracers, to determine the half-life of brain DHA in mice following a dietary switch experiment. Mice fed diets containing either α-linolenic acid (ALA) or DHA as the sole dietary n-3 PUFA were switched onto diets containing ALA, DHA, or ALA + DHA at 6 weeks of age, while control mice were maintained on their respective background diet. We measured brain DHA carbon isotope ratios (reported as δ13CDHA signatures) over a 168-day time course. Brain δ13CDHA signatures of control mice maintained on background diets over the time course were stable (P > 0.05). Brain δ13CDHA signatures of mice switched to the DHA or ALA + DHA diet from the ALA diet changed over time, yielding brain incorporation half-lives of 40 and 34 days, respectively. These half-lives determined by natural abundance carbon isotope ratio analysis were consistent with estimates from kinetic isotope tracer studies. Our results demonstrate the feasibility of natural abundance carbon isotope ratio analysis in the study of fatty acid metabolism without the use of isotopically labeled fatty acid tracers.

Sensitivity boosts by the CPMAS CryoProbe for challenging biological assemblies

Despite breakthroughs in MAS NMR hardware and experimental methodologies, sensitivity remains a major challenge for large and complex biological systems. Here, we report that 3–4 fold higher sensitivities can be obtained in heteronuclear-detected experiments, using a novel HCN CPMAS probe, where the sample coil and the electronics operate at cryogenic temperatures, while the sample is maintained at ambient temperatures (BioSolids CryoProbe™). Such intensity enhancements permit recording 2D and 3D experiments that are otherwise time-prohibitive, such as 2D 15N-15N proton-driven spin diffusion and 15N-13C double cross polarization to natural abundance carbon experiments. The benefits of CPMAS CryoProbe-based experiments are illustrated for assemblies of kinesin Kif5b with microtubules, HIV-1 capsid protein assemblies, and fibrils of human Y145Stop and fungal HET-s prion proteins – demanding systems for conventional MAS solid-state NMR and excellent reference systems in terms of spectral quality. We envision that this probe technology will be beneficial for a wide range of applications, especially for biological systems suffering from low intrinsic sensitivity and at physiological temperatures.

Mechanisms underlying limited soil carbon gains in perennial and cover‐cropped bioenergy systems revealed by stable isotopes

AbstractRemoval of biomass for bioenergy production may decrease soil organic carbon. While perennials or cover‐cropped grains often have greater root production than annual grain crops, they variably impact soil carbon and underlying mechanisms remain unclear. We used high‐frequency measurements of soil respiration and natural abundance carbon stable isotopes to differentiate respiration sources, pool sizes, and decomposition rate constants during a 10 month incubation of soils collected to 1 m depth from a 10 year old field experiment in Iowa, United States. Conversion of corn–soybean rotations to reconstructed prairies or addition of a rye cover crop to continuous corn significantly altered respiration sources and dynamics of fast‐ and slow‐cycling carbon (turnover times of weeks to months–years, respectively), but had little effect on bulk soil carbon and several extractable pools (except in fertilized prairie). Both unfertilized and fertilized prairies increased slow‐cycling carbon pools relative to annual crops, but only in 0–25 cm soil. Compared with fertilized prairie, the unfertilized prairie significantly increased decomposition rates of fast‐ and slow‐cycling carbon pools in 0–25 cm soil, likely explaining the lack of significant bulk soil carbon accrual despite twofold greater root production. Carbon derived from C4 plants decomposed faster than C3‐derived carbon across all depths and cropping systems and contributions of C3‐carbon to respiration increased with depth. Respiration of cover crop‐derived carbon was greatest in 0–25 cm soil but comprised &gt;25% of respiration below 25 cm, implying a disproportionate impact of the cover crop on deep soil metabolism. However, the cover crop also increased the decomposition rates of fast‐ and slow‐cycling carbon pools and decreased their pool sizes across all depths relative to corn without a cover crop. Despite their notable environmental benefits, neither unfertilized perennials nor cover crops necessarily promote rapid soil carbon sequestration relative to conventional annual bioenergy systems because of concomitant increases in decomposition.

Peyssonnosides A-B, Unusual Diterpene Glycosides with a Sterically Encumbered Cyclopropane Motif: Structure Elucidation Using an Integrated Spectroscopic and Computational Workflow.

Two sulfated diterpene glycosides featuring a highly substituted and sterically encumbered cyclopropane ring have been isolated from the marine red alga Peyssonnelia sp. Combination of a wide array of 2D NMR spectroscopic experiments, in a systematic structure elucidation workflow, revealed that peyssonnosides A–B (1–2) represent a new class of diterpene glycosides with a tetracyclo [7.5.0.01,10.05,9] tetradecane architecture. A salient feature of this workflow is the unique application of quantitative interproton distances obtained from the rotating frame Overhauser effect spectroscopy (ROESY) NMR experiment, wherein the β-d-glucose moiety of 1 was used as an internal probe to unequivocally determine the absolute configuration, which was also supported by optical rotatory dispersion (ORD). Peyssonnoside A (1) exhibited promising activity against liver stage Plasmodium berghei and moderate antimethicillin-resistant Staphylococcus aureus (MRSA) activity, with no cytotoxicity against human keratinocytes. Additionally, 1 showed strong growth inhibition of the marine fungus Dendryphiella salina indicating an antifungal ecological role in its natural environment. The high natural abundance and novel carbon skeleton of 1 suggests a rare terpene cyclase machinery, exemplifying the chemical diversity in this phylogenetically distinct marine red alga.

Long‐term fertilization effects on 13C natural abundance, soil aggregation, and deep soil organic carbon sequestration in an Alfisol

AbstractAlthough the 13C (13Carbon) natural abundance method is used to study soil C dynamics, scanty information is available on long‐term fertilization effects on soil C sequestration rates along with δ13C in surface (0–30 cm) and deep (30–90 cm) soil layers and their relationships with crop productivities in subtropics. Hence, soil aggregation, δ13C in bulk soils and aggregates, C pools, and sequestration rates were studied in an Indian Alfisol under a 43‐year old wheat (Triticum aestivum L.)‐based cropping system. Treatments were as follows: no mineral fertilizer and no manure (unfertilized control), 100% recommended dose of nitrogen (N), 100% N and 100% recommended phosphorus (NP), 100% N, 100% P, and 100% recommended potassium (NPK), NPK + lime (NPKL), 150% recommended NPK (1.5NPK), and NPK + farmyard manure at 10 Mg ha−1 (NPKF). Plots with NPKF contained 50% higher soil organic C than NPKL in surface soil (0–15‐cm layer). In the 0–90‐cm profile, soil organic C accumulation and sequestration rates in NPKF were ~0.15 and 0.11 Mg ha−1 yr−1 higher than NPKL plots, respectively. The NPKF plots had higher glomalin‐related soil protein and greater recalcitrant C than NPKL, 1.5NPK, and NPK in surface soil. The NPKF plots had higher δ13C values within bulk soils and their aggregates than NPKL and NPK. There were significant correlations between deep soil C sequestration rates with mean crop productivities and δ13C with deep soil C sequestration rates. Overall, NPKF application had the largest surface and deep soil C sequestration with highest crop productivity and hence is recommended.

Natural Abundance Carbon Isotopic Analysis Indicates the Equal Contribution of Local Synthesis and Plasma Uptake to Palmitate Levels in the Mouse Brain.

Saturated fatty acids are the most abundant fatty acids in the brain, however, there has been some debate regarding the ability of intact dietary saturated fatty acids to be incorporated into the brain. In the present study, we use compound specific isotope analysis to measure the natural abundance carbon isotopic signature of brain, liver, and blood palmitic acid (PAM) and compare it to the dietary PAM and sugar isotopic signatures to calculate the relative contribution of both the incorporation of intact and endogenously synthesized PAM to these pools. Mice were equilibrated to the study diet, and extracted fatty acids were analyzed with gas chromatography isotope ratio mass spectrometry to determine the carbon isotopic signature of PAM (δ13 CPAM ). Liver, serum total, and serum unesterified fatty acid δ13 CPAM ranged between -20.6 and -21.1 mUr and were approximately 8.5 mUr more enriched in 13 C when compared to the dietary PAM signature. Brain δ13 CPAM was found to be more enriched than liver or blood pools (-16.7 ± 0.2 mUr, mean ± SD). Two end-member-mixed modeling using the carbon isotopic signature of dietary PAM and dietary sugars determined the contribution of synthesis to the total tissue PAM pool to range between 44% and 48%. This suggests that endogenous synthesis and dietary PAM are near equal contributors to brain, liver, and blood PAM pools. In conclusion, our data provide evidence that brain PAM levels are maintained by both local endogenous synthesis and through the uptake of intact PAM from the blood.

Facile green synthesis of 3D porous glucose-based carbon aerogels for high-performance supercapacitors

As new-generation carbon materials, carbon aerogels (CAs) offer opportunities in supercapacitor application owing to their excellent properties. Herein, we present a facile, green synthesis of CAs using glucose as carbon source, one of the most important monosaccharide and abundant occurrence in the world, which can be readily available by plants photosynthesis and hydrolysis of disaccharide as well as polysaccharide. To improve the surface area and tailor the pore texture of the CAs, glucose as precursor was treated with an optional activating agent sodium hydroxide to obtain activated CA at 850 °C. SEM, TEM, XRD, XPS and Raman techniques reveal that the as-prepared CA-850 is of graphitized carbon layers and bimodal mesopores, possessing the high specific surface area of 2492.6 m2 g−1 determined by BET characterization. Impressively, as electrode material for supercapacitors, CA-850 exhibits a high specific capacitance of 299 F g−1, energy density of 41.52 Wh kg−1 as well as long-term cycling stability with 99% of the capacitance retention over 1000 cycles. This work will pave the way on the potential use of natural-abundance carbon source for green and mass production of carbon aerogels in supercapacitor applications.

Addition of nitrogen fertiliser increases net ecosystem carbon dioxide uptake and the loss of soil organic carbon in grassland growing in mesocosms

Maintaining and increasing soil organic carbon stocks in grasslands is essential for sustainable productivity and to offset anthropogenic carbon emissions. Direct measurements of net ecosystem carbon dioxide exchange, FN, can be used to detect whether an ecosystem is a net sink or a source of carbon. However partitioning heterotrophic respiration, RH, from ecosystem respiration, RE, is needed to determine the impacts of land-use and global change on soil organic carbon stocks. We extracted intact soil cores from an intensively grazed dairy farm to establish mesocosms growing in controlled conditions and we subjected them to low and high nitrogen treatments (100 and 400kgNha1y−1, respectively). After concurrent clipping and addition of nitrogen, we measured the timing for the recovery of FN and its components, photosynthesis, A, and ecosystem respiration, RE, by measuring them daily. Subsequently, we measured RH from the same mesocosms seven days after the treatments were applied, using a non-disruptive, natural abundance carbon isotope technique. To test the significance of the presence of living roots when measuring RH, we compared the results obtained from the isotopic approach to those obtained from a root exclusion technique, which involved removing the roots from the mesocosms. As the plants grew after clipping, FN decreased (increasing net CO2 uptake) exponentially to mean (±standard error) steady-state values of 1.11±0.26μmolm−2s−1 (net source) and −0.19±0.33μmolm−2s−1 (near neutral) for the low and high nitrogen treatments, respectively. When measured using the isotopic approach, RH increased by 60%, from 1.26±0.29μmolm−2s−1 in the low, to 2.06±0.55μmolm−2s−1 in the high nitrogen treatment. Thus, addition of the high nitrogen resulted in an increase in soil organic carbon loss concurrently with an increase in net uptake of carbon by the ecosystem in the high nitrogen treatment compared with the low nitrogen treatment. When measured in the absence of living roots using the root exclusion technique, RH was overall much higher than the value obtained with the isotopic technique (4.34±0.13μmolm−2s−1), indicating an apparent negative rhizosphere priming effect. Furthermore, when using the root exclusion technique, no difference was found between the nitrogen treatments, suggesting that the presence of roots mediated the response of heterotrophic respiration to addition of nitrogen. These results highlight the need to include measurements of changes in RH alongside measurements of FN in non-disturbed ecosystems to interpret the processes regulating the effects of management practices on long-term changes in soil organic carbon stocks.

Macrophytes and periphyton carbon subsidies to bacterioplankton and zooplankton in a shallow eutrophic lake in tropical China

The subsidy of carbon derived from macrophytes and associated periphyton to bacterioplankton and zooplankton in subtropical shallow eutrophic Huizhou West Lake in China was analyzed using carbon stable isotope signatures. A restored part of the lake dominated by macrophytes was compared with an unrestored phytoplankton-dominated part. Macrophytes, periphyton, seston, and zooplankton were sampled every two months to determine natural-abundance carbon isotope ratios (δ13C). The δ13C of phytoplankton and bacterioplankton was determined from δ13C of fatty acid biomarkers. Macrophytes and associated periphyton had similar δ13C values and were the most enriched in 13C of all measured organic carbon pools. A macrophyte–periphyton carbon isotopic signal was detected in particulate organic carbon, bacterioplankton, and zooplankton in the macrophyte-dominated lake part, which was demonstrated by a significant enrichment in 13C compared with the unrestored part, while phytoplankton and dissolved organic carbon had similar δ13C values in both lake parts. A two-source (macrophytes–periphyton and phytoplankton) mixing model showed that macrophytes–periphyton potentially contributed 14–85% (average 55%) to bacterioplankton in the macrophyte-dominated lake part, depending on season. The macrophytes–periphyton contribution to zooplankton seasonally varied between 26% and 86%, with an average of 47%. The contribution of macrophytes–periphyton to bacterioplankton increased with increasing macrophyte biomass relative to phytoplankton biomass (indicated by chlorophyll a). Carbon from macrophytes with associated periphyton subsidizes bacterioplankton and zooplankton, likely enhancing the cascading effects of planktonic food webs, providing an additional explanation for the stability of a clear-water state in shallow lakes dominated by macrophytes.

Minimal incorporation of Deepwater Horizon oil by estuarine filter feeders

Natural abundance carbon isotope analyses are sensitive tracers for fates and use of oil in aquatic environments. Use of oil carbon in estuarine food webs should lead to isotope values approaching those of oil itself, −27‰ for stable carbon isotopes reflecting oil origins and −1000‰ for carbon-14 reflecting oil age. To test for transfer of oil from the 2010 Deepwater Horizon spill into estuarine food webs, filter-feeding barnacles (Balanus sp.) and marsh mussels (Geukensia demissa) were collected from Louisiana estuaries near the site of the oil spill. Carbon-14 analyses of these animals from open waters and oiled marshes showed that oil use was <1% and near detection limits estimated at 0.3% oil incorporation. Respiration studies showed no evidence for enhanced microbial activity in bay waters. Results are consistent with low dietary impacts of oil for filter feeders and little overall impact on respiration in the productive Louisiana estuarine systems.