Amount Of 14C Research Articles

Root derived carbon transport extends the rhizosphere of rice compared to wheat

Upland and paddy soils are two main agricultural land-use types. Differences in the transportation and distribution of root-derived C between these two soil types are of great significance, but given less attention. In the current study, a pot experiment with rhizobox (one root zone and four outer zones) was conducted in a continuous 13C-CO2 labelling chamber, cultivating rice (paddy soil) and wheat (upland soil), respectively. 13C abundances of soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC) and bacterial community composition were measured after labelling. The 13C atom% of SOC, DOC and MBC was lower in the root zone but higher in non-rhizosphere paddy soil, when compared with the upland soil. Similar amounts of 13C were recovered in these two soils. In the upland soil, 83.5% of total 13C was retained in the rhizosphere, while 71.4% in the paddy soil was transported to outer zones. Furthermore, there was a sharp decrease of root-derived C and concomitantly an abrupt succession of bacterial community between the root compartment and outer zones in the upland soil, indicating a narrow extension of wheat rhizosphere. In contrast, more gradual variations in carbon distribution and bacterial community composition were seen in the paddy soil, with a clear evidence of a transition zone. In conclusion, compared with the upland soil, more root-derived carbon is transported from rhizosphere to bulk soil in paddies, which leads to a wider range of rhizosphere and a higher rhizosphere effect. These results are helpful to understand the widely accepted distinctions in soil C stock and productivity sustainability between upland and paddy soils. It may shed light on a new perspective for improving soil fertility, especially in upland cropping systems.

Tibetan sedges sequester more carbon belowground than grasses: a 13C labeling study

The Kobresia meadows widely distributed on the Tibetan Plateau are very tolerant to intensive grazing. The plant communities in these meadows are currently undergoing a shift in dominance from Cyperaceae (sedges) to Gramineae (grasses) species. We investigated the effects of the replacement of sedges by grasses in an alpine meadow on the allocation of photosynthetic carbon (C) in various plant and soil pools. We selected patches (50 cm × 50 cm) of two vegetation types dominated by sedges (Kobresia capillifolia, K. humilis and Carex spp., accounting for 88% of the total shoot biomass) and grasses (Elymus nutans, Poa crymophila and Leymus secalinus, accounting for 86% of the total shoot biomass), respectively, in an alpine pasture grazed by yaks (Bos grunniens) and sheep (Ovis aries) in the winter season (November–June). Photoassimilate partitioning in various plant and soil pools was compared between sedge- and grass-dominated patches in the peak growth season (August) after labeling of plants in a 13CO2 atmosphere. The sedge-dominated patches had 85% smaller aboveground biomass but a much larger ratio of root (in the 0–50 cm soil depth) to shoot biomass (23.0 under sedges vs. 9.5 under grasses) than the grass-dominated patches. However, similar 13C amounts were assimilated by sedges (1651 mg C m−2) and grasses (1575 mg C m−2) during 2 h of labeling, showing a greater capacity to assimilate C per unit of aboveground biomass in sedges. Over the period of 32 days after labeling, 13C allocation to roots and soil was consistently greater under sedges than under grasses. By day 32 after labeling, the total 13C amount remaining in roots and soil down to 50 cm depth was greater under sedges (78.5% of the total 13C assimilated) than under grasses (65.7%). Although similar C amounts were assimilated by two plant functional groups, sedges transferred more C to roots and soil (through rhizodeposition) than the grasses. This reflects the greater root-to-shoot ratio of sedges than grasses. Consequently, the ongoing replacement of sedges by grasses in plant communities will decrease soil C sequestration in the Kobresia meadows of the Tibetan Plateau.

Fatty Acid Composition of Muscles Tissues of Longdong Goat (Black and White Cashmere)

This study examined fatty acid (FA) composition of muscle tissue of Longdong black goat and Longdong white Cashmere goat breed under reared systems. Approximately 86.31% of fatty acids were observed. Oleic acid was extensively the most abundant ranged from 22.98% to 26.02% of Longdong black and white Cashmere goat respectively. The mean amount of SFA and MUFA were about 21.46% to 34.82% respectively. PUFA were 30.02% of total FA composition. C20:4 were founded 12.14% in all muscles tissues. Compare to C20:5, C22:6 16.43%, 4.88% respectively. The amount of SFA: MUFA ratio was low in Longdong goat muscles tissues. PUFA and MUFA had higher amount female black muscles tissues. Females and males of both had great amount of C16:0, C18:0, ranged from 0.86% to 29.16%. C18:2 were found in 15.01%. The study found fatty acids composition in both Longdong goat breed (black and white cashmere) has some significant effect (P<0:05) in fatty acids proportions. The greater ratios of unsaturated fatty acids MUFA and PUFA high amount than saturated fatty acids SFA in goat muscle tissue and this indicate that Longdong goats breed are healthier and have the same type of fatty acids composition.

Glucose mineralization in soils of contrasting textures under application of S-metolachlor, terbuthylazine, and mesotrione, alone and in a mixture

ABSTRACT Microbial adaptation may occur in surface soils under agricultural uses exposed to herbicides. However, little is known about herbicide mixture effects in the soil, especially in tropical regions like Brazil. The aim of this study was to evaluate glucose mineralization in soils of contrasting textures (sandy clay and sandy loam) from areas cultivated with maize under application of S-metolachlor, terbuthylazine and mesotrione, alone and in a mixture. The methodology was established according to the soil microorganisms: carbon transformation test with 14C-glucose solution (D-[U-14C] glucose) in biometric flasks. After the addition of 14C-glucose, the amount of 14C in cumulative CO2 of microbial respiration was measured several times during the 28-day incubation. For unamended soil control (without herbicide), microbial activity followed a similar behavior to amended soil with herbicides in total 14CO2 released and accumulated, ranging from 23 to 27%. Overall, mineralization constant rate (k) values for all treatments were also similar, with an average value of 0.0038% CO2.d–1. Consequently, mineralization half-life times (MT50) were from 173 to 198 d. Microbial respiration for all treatments was slightly higher in the sandy clay compared with sandy loam soil; although soil samples with application of herbicides (alone and in a mixture) did not show decreased basal microbial respiration or mineralization rates of glucose. To corroborate these findings, additional research with different organic substrates and in cultures with different applications of herbicides are needed to prove the non interference of these herbicides on the microbial respiration in the soil.

Rhizodeposition under drought is controlled by root growth rate and rhizosphere water content

Rhizodeposition is an important energy source for soil microorganisms. It is therefore crucial to estimate the distribution of root derived carbon (C) in soil and how it changes with soil water content. We tested how drought affects exudate distribution in the rhizosphere by coupling 14CO2 labelling of plants and phosphor imaging to estimate C allocation in roots. Rhizosphere water content was visualized by neutron radiography. A numerical model was employed to predict the exudate release and its spatiotemporal distribution along and around growing roots. Dry and wet plants allocated similar amounts of 14C into roots but root elongation decreased by 48% in dry soil leading to reduced longitudinal rhizosphere extension. Rhizosphere water content was identical (31%) independent of drought, presumably because of the high water retention by mucilage. The model predicted that the increase in rhizosphere water content will enhance diffusion of exudates especially in dry soil and increase their microbial decomposition. Root growth and rhizosphere water content play an important role in C release by roots and in shaping the profiles of root exudates in the rhizosphere. The release of mucilage may be a plant strategy to maintain fast diffusion of exudates and high microbial activity even under water limitation.

Butter serums and buttermilks as sources of bioactive lipids from the milk fat globule membrane: Differences in their lipid composition and potentialities of cow diet to increase n-3 PUFA

Improving the nutritional and health properties of food products, e.g. infant milk formula, by the addition of functional ingredients is of primary importance. This study focused on bioactive milk polar lipids (PLs) recovered from dietary sources that are of increasing interest. The chemical compositions of buttermilks and butter serums were determined and the modulation of the fatty acid composition of milk PLs was investigated. Butter serums contain a higher amount of milk PLs than buttermilks (88 vs. 13–18g/kg dry matter), with a higher proportion of sphingomyelin (34 vs. 19% of PLs, respectively) interestingly close to human milk PL profile. Butter serums are also interesting sources of choline, an important nutrient for infant brain development. We demonstrated that the unsaturated fatty acid content of milk PLs recovered in the buttermilks and the butter serums, mainly the amount of C18:3n-3 and C22:6n-3 (DHA) that are of nutritional interest, can be increased by dietary strategies. This work opens perspectives for a better valorization of milk PLs in human nutrition (both infants and adults) to benefit their functional, nutritional and health properties.

Changes in the chemical and physical characteristics of cow’s milk butter during storage: Effects of temperature and addition of salt

The effect of storage at 4°C or 12°C on cow‘s milk butter manufactured without or with salt (2.1%) was examined. Storage of the butter for 9 months scarcely affected the fatty acid contents, and only the amounts of C18:3 n–3, C20:5 n–3 and C22:2 n–6 decreased significantly in the total lipid fraction. The total amount of free fatty acids increased significantly during storage (from 136–167 to 360–575mg/100g of fat), and both the addition of salt and the higher storage temperature enhanced the release of fatty acids from lipids. The free fatty acid contents (360–575mg/100g of fat) and the values of the parameters indicating lipolysis (acidity value: 1.89–2.18mg KOH/g of fat; degree of acidity: 0.95–1.09% oleic acid) at the end of the storage period indicate that butter undergoes very slight lipolysis. The values of parameters indicating fat oxidation (peroxide value and TBA value) increased significantly during storage (from 0.38–0.39 to 0.90–3.75meq. O2/kg of fat, and from 0.084–0.1 to 0.093–0.220mg malondialdehyde/kg, respectively), and both the addition of salt and the increase in storage temperature had enhancing effects on the oxidative processes. The b* values increased significantly during storage, while a* and L* values decreased. In conclusion, cow’s milk butter was hardly modified during refrigerated storage, while both the addition of salt and the increase in storage temperature increased lipolytic and oxidative changes.

Serum Phospholipid Fatty Acid Composition in Cystic Fibrosis Patients with and without Liver Cirrhosis

Background/Aims: Cystic fibrosis (CF) liver disease is the third most frequent cause of death in CF patients. Although it alters fatty acid (FA) metabolism, data concerning the profile of FA in CF patients with liver cirrhosis is lacking. This study aimed to assess the FA composition of serum phospholipids in CF patients with and without liver cirrhosis. Methods: The study comprised 25 CF patients with liver cirrhosis and 25 without it. We assessed Z-scores for body height and weight, lung function, exocrine pancreatic sufficiency and colonization with Pseudomonas aeruginosa. FAs' profile of serum glycerophospholipids was quantified by gas chromatography mass spectrometry. Results: In CF patients with liver cirrhosis, the levels of C16:0 were higher and the amounts of C20:2n-6, C20:3n-6, C20:4n-6, and all the n-3 polyunsaturated FAs (PUFAs) (C18:3n-3, C20:5n-3, C22:5n-3, C22:6n-3) were lower than those in CF subjects without liver cirrhosis. The n-6/n-3, C20:4n-6/C18:2n-6, total n-6/C18:2n-6, C20:5n-3/C18:3n-3 and total n-3/C18:3n-3 ratios did not differ between the 2 groups. Conclusions: Liver cirrhosis may associate with profound abnormalities in the composition of serum glycerophospholipids FAs in CF patients. None of the analyzed clinical factors could explain the greater prevalence of low levels of PUFAs in this CF subgroup.

Patterns and dynamics of neutral lipid fatty acids in ants \u2013 implications for ecological studies

BackgroundTrophic interactions are a fundamental aspect of ecosystem functioning, but often difficult to observe directly. Several indirect techniques, such as fatty acid analysis, were developed to assess these interactions. Fatty acid profiles may indicate dietary differences, while individual fatty acids can be used as biomarkers. Ants are among the most important terrestrial animal groups, but little is known about their lipid metabolism, and no study so far used fatty acids to study their trophic ecology. We set up a feeding experiment with high- and low-fat food to elucidate patterns and dynamics of neutral lipid fatty acids (NLFAs) assimilation in ants. We asked whether dietary fatty acids are assimilated through direct trophic transfer, how diet influences NLFA total amounts and patterns over time, and whether these assimilation processes are similar across species and life stages.ResultsAnts fed with high-fat food quickly accumulated specific dietary fatty acids (C18:2n6, C18:3n3 and C18:3n6), compared to ants fed with low-fat food. Dietary fat content did not affect total body fat of workers or amounts of fatty acids extensively biosynthesized by animals (C16:0, C18:0, C18:1n9). Larval development had a strong effect on the composition and amounts of C16:0, C18:0 and C18:1n9. NLFA compositions reflected dietary differences, which became more pronounced over time. Assimilation of specific dietary NLFAs was similar regardless of species or life stage, but these factors affected dynamics of other NLFAs, composition and total fat.ConclusionsWe showed that ants accumulated certain dietary fatty acids via direct trophic transfer. Fat content of the diet had no effect on lipids stored by ants, which were able to synthesize high amounts of NLFAs from a sugar-based diet. Nevertheless, dietary NLFAs had a strong effect on metabolic dynamics and profiles. Fatty acids are a useful tool to study trophic biology of ants, and could be applied in an ecological context, although factors that affect NLFA patterns should be taken into account. Further studies should address which NLFAs can be used as biomarkers in natural ant communities, and how factors other than diet affect fatty acid dynamics and composition of species with distinct life histories.

Stimulation and inhibition of enzymatic hydrolysis by organosolv lignins as determined by zeta potential and hydrophobicity

BackgroundLignin typically inhibits enzymatic hydrolysis of cellulosic biomass, but certain organosolv lignins or lignosulfonates enhance enzymatic hydrolysis. The hydrophobic and electrostatic interactions between lignin and cellulases play critical roles in the enzymatic hydrolysis process. However, how to incorporate these two interactions into the consideration of lignin effects has not been investigated.ResultsWe examined the physicochemical properties and the structures of ethanol organosolv lignins (EOL) from hardwood and softwood and ascertained the association between lignin properties and their inhibitory and stimulatory effects on enzymatic hydrolysis. The zeta potential and hydrophobicity of EOL lignin samples, isolated from organosolv pretreatment of cottonwood (CW), black willow (BW), aspen (AS), eucalyptus (EH), and loblolly pine (LP), were determined and correlated with their effects on enzymatic hydrolysis of Avicel. EOLs from CW, BW, and AS improved the 72 h hydrolysis yield by 8–12%, while EOLs from EH and LP decreased the 72 h hydrolysis yield by 6 and 16%, respectively. The results showed a strong correlation between the 72 h hydrolysis yield with hydrophobicity and zeta potential. The correlation indicated that the hydrophobicity of EOL had a negative effect and the negative zeta potential of EOL had a positive effect. HSQC NMR spectra showed that β-O-4 linkages in lignin react with ethanol to form an α-ethoxylated β-O-4ʹ substructure (Aʹ) during organosolv pretreatment. Considerable amounts of C2,6–H2,6 correlation in p-hydroxybenzoate (PB) units were observed for EOL–CW, EOL–BW, and EOL–AS, but not for EOL–EH and EOL–LP.ConclusionsThis study revealed that the effect of lignin on enzymatic hydrolysis is a function of both hydrophobic interactions and electrostatic repulsions. The lignin inhibition is controlled by lignin hydrophobicity and the lignin stimulation is governed by the negative zeta potential. The net effect of lignin depends on the combined influence of hydrophobicity and zeta potential. This study has potential implications in biomass pretreatment for the reduction of lignin inhibition by increasing lignin negative zeta potential and decreasing hydrophobicity.

Effects of complexation between organic matter (OM) and clay mineral on OM pyrolysis

The stability and persistence of organic matter (OM) in source rocks are of great significance for hydrocarbon generation and the global carbon cycle. Clay-OM associations commonly occur in sedimentation and diagenesis processes and can influence the pyrolytic behaviors of OM. In this study, clay-OM complexes, i.e., interlayer clay-OM complexes and clay-OM mixture, were prepared and exposed to high-pressure pyrolysis conditions in confined gold capsule reactors to assess variations in OM pyrolysis products in the presence of clay minerals. Three model organic compounds, octadecanoic acid (OA), octadecy trimethyl ammonium bromide (OTAB), and octadecylamine (ODA), were employed and montmorillonite (Mt) was selected as the representative clay mineral. The solid acidity of Mt plays a key role in affecting the amount and composition of the pyrolysis gases generated by the clay-OM complexes. The Brønsted acid sites significantly promote the cracking of hydrocarbons through a carbocation mechanism and the isomerization of normal hydrocarbons. The Lewis acid sites are primarily involved in the decarboxylation reaction during pyrolysis and are responsible for CO2 generation. Mt exhibits either a catalysis effect or pyrolysis-inhibiting during pyrolysis of a given OM depending on the nature of the model organic compound and the nature of the clay-OM complexation. The amounts of C1–5 hydrocarbons and CO2 that are released from the Mt-OA and Mt-ODA complexes were higher than those of the parent OA and ODA, respectively, indicating a catalysis effect of Mt. In contrast, the amount of C1–5 hydrocarbons produced from the pyrolysis of Mt-OTAB complexes was lower than that of OTAB, which we attribute to an inhibiting effect of Mt. This pyrolysis-inhibiting effect works through the Hoffmann elimination that is promoted by the catalysis of the Brønsted acid sites of Mt, therefore releasing smaller amounts of gas hydrocarbons than the nucleophilic reaction that is induced by the halide ions in OTAB. In particular, the interlayer space of Mt acts as an ‘amplifier’ that magnifies the above-mentioned catalysis or pyrolysis-inhibiting effect, due to the greater number of Brønsted acid sites with high acidity in the interlayer space. These findings are potentially important for understanding the storage and transfer mechanisms of natural OM in sedimentation and diagenesis processes.

Lipid accumulation and anti-rotifer robustness of microalgal strains isolated from Eastern China

Large-scale production of biofuels and other high-value products from microalgae focuses on strain selection with desired characteristics such as high lipid productivity and robustness. However, microalgae often suffer severe biomass losses due to contamination that comes in the form of herbivores, especially rotifers. In this study, we found that the total lipid content of 54 microalgal strains from Eastern China ranged from 12.6 to 59.9% of dry cell weight (dw), with an average of 35.4% dw. Lipid productivity of these microalgal strains varied from 0.04 to 0.14 g L−1 day−1, and 15 showed lipid production rates over 0.10 g L−1 day−1. The fatty acid profiles of 34 microalgal strains with lipid content over 40% dw were analyzed by gas chromatography. We found that the amount of C18:1 increased with increasing total lipid content, whereas C14:0 and C16:0 showed a negative correlation to the total amount of lipids. An experimental rotifer-microalgae predator-prey model was constructed, and the anti-rotifer robustness of these microalgal strains was evaluated. We found that Didymogenes sp. HN-4 can depress the growth of rotifers significantly. This study demonstrates the biodiversity of the native Chinese microalgae in lipid productivity and robustness, which lays the groundwork for mass algal culture.

Fate of rice shoot and root residues, rhizodeposits, and microbial assimilated carbon in paddy soil - part 2: turnover and microbial utilization

The turnover of plant- and microbial- derived carbon (C) plays a significant role in the soil organic C (SOC) cycle. However, there is limited information about the turnover of the recently photosynthesized plant- and soil microbe-derived C in paddy soil. We conducted an incubation study with four different 13C–labeled substrates: rice shoots (Shoot-C), rice roots (Root-C), rice rhizodeposits (Rhizo-C), and microbe-assimilated C (Micro-C). Shoot- and Root-C were initially rapidly transformed into the dissolved organic C (DOC) pool, while their recovery in microbial biomass C (MBC) and SOC increased with incubation time. There were 0.05%, 9.8% and 10.0% of shoot-C, and 0.06%, 15.9% and 16.5% of root-C recovered in DOC, MBC and SOC pools, respectively at the end of incubation. The percentages of Rhizo- and Micro-C recovered in DOC, MBC, and SOC pools slowly decreased over time. Less than 0.1% of the Rhizo- and Micro-C recovered in DOC pools at the end of experiment; while 45.2% and 33.8% of Rhizo- and Micro-C recovered in SOC pools. Shoot- and Root-C greatly increased the amount of 13C–PLFA in the initial 50 d incubation, which concerned PLFA being indicative for fungi and actinomycetes while those assigning gram-positive bacteria decreased. The dynamic of soil microbes utilizing Rhizo- and Micro-C showed an inverse pattern than those using Shoot- and Root-C. Principal component analysis of 13C–PLFA showed that microbial community composition shifted obviously in the Shoot-C and Root-C treatments over time, but that composition changed little in the Rhizo-C and Micro-C treatments. The input C substrates drive soil microbial community structure and function with respect to carbon stabilization. Rhizodeposited and microbial assimilated C have lower input rates, however, they are better stabilized than shoot- and root-derived C, and thus are preferentially involved in the formation of stable SOC in paddy soils.

Evaluation of bi-functionalized mesoporous silicas as reversed phase/cation-exchange mixed-mode sorbents for multi-residue solid phase extraction of veterinary drug residues in meat samples

A SBA-15 type mesoporous silica was synthesized and bi-functionalized with octadecylsilane (C18) or octylsilane (C8), and sulfonic acid (SO3-) groups in order to obtain materials with reversed-phase/strong cation-exchange mixed-mode retention mechanism. The resulting hybrid materials (SBA-15-C18-SO3- and SBA-15-C8-SO3-) were comprehensively characterized. They showed high surface area, high pore volume and controlled porous size. Elemental analysis of the materials revealed differences in the amount of C18 and C8. SBA-15-C18-SO3- contained 0.19mmol/g of C18, while SBA-15-C8-SO3- presented 0.54mmol/g of C8. The SO3- groups anchored to the silica surface of the pore walls were 0.20 and 0.09mmol/g, respectively. The bi-functionalized materials were evaluated as SPE sorbents for the multi-residue extraction of 26 veterinary drug residues in meat samples using ultra-high-performance liquid chromatography coupled to mass spectrometry detector (UHPLC-MS/MS). Different sorbent amounts (100 and 200mg) and organic solvents were tested to optimize the extraction procedure. Both silicas showed big extraction potential and were successful in the extraction of the target analytes. The mixed-mode retention mechanism was confirmed by comparing both silicas with SBA-15 mesoporous silica mono-functionalized with C18 and C8. Best results were achieved with 200mg of SBA-15-C18-SO3- obtaining recoveries higher than 70% for the majority of analytes.

Mechanisms of inorganic carbon-14 attenuation in contaminated groundwater: Effect of solution pH on isotopic exchange and carbonate precipitation reactions

Radioactive 14C is a significant contaminant associated with nuclear fuels and wastes that is potentially highly mobile in the environment as dissolved inorganic carbonate species. This study investigated the mechanisms by which dissolved inorganic 14C is retained in surface and groundwater environments via precipitation and isotopic exchange reactions. Precipitation of calcite in the presence and absence of nucleation sites is considered along with isotopic exchange with both atmospheric CO2 and solid carbonates. Precipitation occurs at calcite supersaturation values of SICAL > 1.5 in the absence of nucleation sites and SICAL > 0–0.5 in the presence of nucleation sites, suggesting that precipitation of 14C-bearing carbonates is much more likely in subsurface environments where nucleation sites are abundant. The maximum 14C removal in solid isotopic exchange experiments occurred after approximately 2 weeks equilibration. In these experiments the amount of 14C removed from solution was proportional to the amount of calcite surface area present, and removal from solution was equivalent to rapid equalisation of the isotope ratio in an 8–10 Å active surface layer. Although the reactivity of natural carbonates may be lower than the calcite samples used in this study, these results suggest isotopic exchange with solids will be an important 14C retardation mechanism in subsurface environments containing only modest TIC concentrations. These results suggest that if inorganic 14C is released into sub-surface environments, both precipitation and solid phase isotopic exchange can result in non-conservative 14C-DIC transport and 14C contamination may persist in groundwater for decades following accidental releases. In contrast, in experiments open to atmosphere with pH values below 9.3, complete loss of dissolved inorganic 14C was very rapid and occurred with timescales of 10's of hours. 14C loss was due to a rapid exchange of dissolved 14C species with 12CO2 (g) and the kinetics of 14C removal increased as pH values were lowered (i.e. atmospheric isotopic exchange was first order with respect to the concentration of carbonic acid present). Thus these results suggest that release of inorganic 14C to surface waters with pH values <9.3 would result in rapid exchange with 12CO2 (g) and 14C would not persist in the aqueous environment, whereas 14C-DIC released to saturated subsurface environments may persist close to the release site for decades due to precipitation and solid phase exchange reactions preventing/retarding transport with the groundwater.

Thermal decomposition products of various carbon sources in chemical vapor deposition synthesis of carbon nanotube

We have studied the thermal catalytic decomposition of different typical carbon sources and an unsuitable carbon source in order to gain insight into the chemical vapor deposition of carbon nanotubes. The suitable sources decomposed into C1 and C2 hydrocarbons and their radicals. In contrast, the unsuitable source did not afford hydrocarbons. In this study, pure methane and ethylene pyrolysis resulted in little amounts of C1 and C2 radicals, and so an excess of hydrogen was required to shift the equilibrium reaction between C1 and C2.

Crop residue quality and soil type influence the priming effect but not the fate of crop residue C

Crop residues and soil types play an important role in soil C and N storage. The objectives of this study were to quantify the effects of crop residue quality and interactions with soil type on soil C and N, in the short- and medium-term, and to determine the responses related to the priming effect (PE). Residues of vetch (Vicia sativa L.), pea (Pisum sativum L.) and wheat (Triticum aestivum L.) crops with different chemical compositions and labelled with 13C and 15N were left to decompose on the surface of either a sandy-loam soil or a clay soil incubated under laboratory conditions at 25 °C for 360 days. We measured the total CO2-C and CO2-13C emitted during decomposition, the soil mineral N content and the amounts of 13C and 15N remaining in both the surface residue particles and the bulk soil. Over the short-term, the vetch residues decomposed faster than those of wheat and pea on the soil surface due to their more favourable chemical composition for biodegradation; after one year, however, this difference disappeared. We observed extra soil C mineralization in all cases, i.e., the PE was positive for all treatments and was directly related to the water-soluble (vetch > pea > wheat) and soil C contents (clay soil > sandy-loam soil). Conversely, the fate of the added 15N and net N mineralization differed considerably between the three residues and was strongly related to the initial N content of the residue. Crop residue quality and soil type affected the soil PE and soil C balance but not the fate of crop residue-C after one year. Net soil N mineralization was observed in all crop residues, with large early differences (vetch > pea > wheat), which were maintained on a medium-term basis. Our results emphasize the need to jointly consider C and N dynamics as well as short- and medium-term effects to manage agricultural and environmental services provided by the recycling of crop residues to agricultural soils.

Microbial community response to changes in substrate availability and habitat conditions in a reciprocal subsoil transfer experiment

While habitat conditions influencing the abundance of microorganisms in topsoil are well known, these dynamics have been largely unexplored in deeper soil horizons. We investigated the effects of different substrate availabilities and environmental conditions on microbial community composition and carbon flow into specific groups of microorganisms in subsoils using a reciprocal soil transfer experiment within an acid and sandy Dystric Cambisol from a ∼100-year old European beech (Fagus sylvatica L.) forest in Lower Saxony, Germany. Containers filled with subsoil from 10 to 20 cm (SUB20) and 110 to 120 cm (SUB120) soil depths and with additions of different amounts of 13C labelled cellulose (1% and 5% of the respective organic carbon content of both soil layers) were exposed either in their home field environment or transferred reciprocally between SUB20 and SUB120 horizons for periods of one, four and twelve months. During the exposure of twelve months, 13C accumulated up to 15 percent in total microbial biomass and up to 25 percent in fungal PLFAs. Similar microbial 13C incorporation rates in SUB20 samples located at either 20 or 120 cm depth indicated comparable microclimatic conditions in both soil environments with no depth-dependent effects on the decomposer communities. While low nitrogen availability (when primary C-limitation was alleviated) and water content limited bacterial growth and activity at both depths, fungal abundance and activity were less affected due to their ability to efficiently exploit resources in surrounding soil by hyphal growth and higher drought resistance. Consequently, bacterial PLFAs (phospholipid fatty acids) incorporated less 13C than fungi. The relatively high, from 1% to 5% cellulose addition linearly increased, 13C incorporation rates in SUB120 samples at 120 cm depth clearly showed the potential of efficient carbon turnover in deeper soil layers. Spatial separation between subsoil microorganisms and their substrates may therefore be an important factor influencing carbon accumulation in subsoil.

The effect of temperature and substrate quality on the carbon use efficiency of saprotrophic decomposition

Background and aimsMineralization of soil organic matter (SOM) constitutes a major carbon flux to the atmosphere. The carbon use efficiency (CUE) of the saprotrophic microorganisms mineralizing SOM is integral for soil carbon dynamics. Here we investigate how the CUE is affected by temperature, metabolic conditions, and the molecular complexity of the substrate.MethodsWe incubated O-horizon soil samples (with either 13C–glucose or 13C–cellulose) from a boreal coniferous forest at 4, 9, 14, and 19 °C, and calculated CUEs based on the amount of 13C–CO2 and 13C–labelled microbial biomass produced. The effects of substrate, temperature, and metabolic conditions (representing unlimited substrate supply and substrate limitation) on CUE were evaluated.ResultsCUE from metabolizing glucose was higher as compared to cellulose. A slight decrease in CUE with increasing temperature was observed in glucose amended samples (but only in the range 9–19 °C), but not in cellulose amended samples. CUE differed significantly with metabolic conditions, i.e. CUE was higher during unlimited growth conditions as compared to conditions with substrate limitation.ConclusionsWe conclude that it is integral to account for both differences in CUE during different metabolic phases, as well as complexity of substrate, when interpreting temperature dependence on CUE in incubation studies.

Deep Water Horizon oil and methane carbon entered the food web in the Gulf of Mexico

AbstractThe Deep Water Horizon (DWH) incident caused the release of an unprecedented amount of 13C‐ and 14C‐depleted oil and gas to the Gulf of Mexico (GoM), which formed surface slicks and deep oil/gas plumes that extended laterally at 1000–1200 m. We conducted three research cruises between 2010 and 2012 to study the potential assimilation of petrocarbon (C derived from oil and/or gas) into the GoM microbial food web. In 2010, we found low δ13C (−30 to −25‰) and Δ14C (−603 to −55‰) values for suspended particles at 1000–1200 m depth as far as 289 km SW of the wellhead, providing direct evidence of the spatial extent of the subsurface plumes. At those depths in 2010, methane and oil carbon accounted for up to 28% and 62% of total particulate carbon (Csp), respectively. In the total area affected by the DWH, 80 ± 56 to 104 ± 91 tonnes (t) of methane‐derived and 216 ± 174 to 292 ± 165 t of oil‐derived carbon were incorporated into Csp. In 2011 and 2012, the δ13C values were distributed throughout the water column indicating that petrocarbon was still present and recycling, especially in the section closest to the DWH, where oil supplied up to 53% and 75% of Csp, respectively. Relatively low δ15N (&lt; 4‰) values in suspended particles at 1000–1200 m in 2010 indicate stimulation of nitrogen fixation linked to methane oxidation in the months after the spill, which accounted for up to 40% of the particulate nitrogen in the water column at those depths.