C3 Plant Material Research Articles

Benchmarking source specific isotopic ratios of levoglucosan to better constrain the contribution of domestic heating to the air pollution

We report source specific isotope ratios of levoglucosan, the specific biomass burning tracer, in aerosol particles from the combustion of selected woods used for domestic heating in Europe, of coals containing cellulose (lignites) as well as of corn, a C4 plant. Here, we combine compound specific δ13C measurements of levoglucosan with total carbon δ13C of parent materials, to assess isotopic fractionations due to biosynthetic pathways or combustion processes. Levoglucosan formed during the combustion of cellulose from coals shows with δ13C of −21.1‰ and −18.6‰ a moderate enrichment in the heavier isotope compared to the C3 plant samples. Contrarily, observed levoglucosan isotope ratios of −25.0 to −21.5‰ for C3 plant samples are significantly lower than for the C4 plant sample (−12.4‰), as expected from the stronger 13C discrimination during the carbon fixation process by C3 compared to C4 plants. Overall, the C4 plant sample shows a 13C enrichment in all bulk measurements, on average by 12.2‰, 14.2‰ and 14.2‰ for total carbon (TC) in aerosol particle, whole plant/coal material and cellulose samples, respectively. Further, δ13C measurements of levoglucosan and TC for biomass burning aerosol particles, bulk plant/coal and cellulose in C3 plant samples agree well with the published observations. The combined levoglucosan/TC isotopic analyses can be used to differentiate among C3/coal/C4 origin of the smoke emissions from the cellulose-containing-fuel combustion. Noticeably, there is a consistent δ13C offset between C3 plant material and levoglucosan, which allows deriving emission levoglucosan isotope ratios when the combusted plant types are known.

The Lability and Source of Particulate Organic Matter in the Northern Gulf of Mexico Hypoxic Zone

AbstractDecomposition of particulate organic matter (POM) plays a key role in the formation of hypoxia in subsurface waters of coastal ocean, yet little is known about the lability and transformation of POM in the hypoxic zone. Suspended particles were collected from surface waters to overlying waters (~30 cm above the sediment‐water interface) along the shelf of northern Gulf of Mexico (nGOM) in late spring/early summer of 2010–2013. Total hydrolyzable amino acids (THAA) and pigments were measured in these particulate samples to trace organic matter lability. The degradation indices, derived from the THAA and chloropigments, were positively correlated with dissolved oxygen (DO) concentrations in the shelf region, suggesting that decomposition of POM contributed greatly to DO utilization. Bacterial degradation appears to be the major pathway for POM decomposition on both inner and mid shelves, while zooplankton grazing played a minor role. POM samples in the overlying water on the inner shelf were the most degraded from the THAA and pigment results, and they also had high C/N ratios (9–14) and depleted δ 13C values (−29‰ to −24‰), pointing to a source of terrestrial C3 plant material. This distinct terrestrial signal of POM in the overlying water suggests strong selective degradation of marine‐sourced organic matter, but how the terrestrial organic matter is settled to this layer and its ultimate fate remain unclear. Taken together, these data offer new angles looking into the lability and degradation pathways of POM, and mechanisms of hypoxia formation in coastal waters.

Stable Nitrogen and Carbon Isotope Signatures (δ 15N and δ 13C Values in ‰) of Fresh and Preserved Button Mushrooms (Agaricus bisporus) from the German Market

Fresh and preserved button mushrooms (Agaricus bisporus) are among the most consumed varieties worldwide. The cultivation is highly optimized and largely based on the use of different compost materials from agricultural wastes as substrates. In this study, we determined the stable carbon (13C) and nitrogen (15N) isotope signatures of the fruiting bodies and used the measured δ values (‰) to obtain indirect information on the medium on which they were grown. The δ 13C values (‰) of the investigated fresh and processed button mushrooms from the German market were quite narrow (δ 13C values −24.8 ± 0.9 ‰, n = 72), which indicated C3 plant materials as carbon sources. Overall high δ 15N values (δ 15N values > 5.5 ‰) of the cultivated mushrooms enabled a differentiation to wild growing saprophytes. Furthermore, the broad range of δ 15N values (Δ=7 ‰) pointed toward a cultivation on compost materials with varying shares of farmyard manure. While only few samples suggested a cultivation on dominantly plant-based substrates, more than 50% of the investigated button mushrooms were related to high shares of animal manures in the compost mixture. Little variation of δ 15N values (‰) in related products collected on subsequent years indicated a high level of standardization of the individual cultivation processes over several years. Analysis of the carbon and nitrogen isotope signatures of cultivated button mushrooms could thus be valuable parameters used for long-term monitoring and controlling purposes.

Dietary versatility of Early Pleistocene hominins

New geochemical data from the Malawi Rift (Chiwondo Beds, Karonga Basin) fill a major spatial gap in our knowledge of hominin adaptations on a continental scale. Oxygen (δ18O), carbon (δ13C), and clumped (Δ47) isotope data on paleosols, hominins, and selected fauna elucidate an unexpected diversity in the Pleistocene hominin diet in the various habitats of the East African Rift System (EARS). Food sources of early Homo and Paranthropus thriving in relatively cool and wet wooded savanna ecosystems along the western shore of paleolake Malawi contained a large fraction of C3 plant material. Complementary water consumption reconstructions suggest that ca. 2.4 Ma, early Homo (Homo rudolfensis) and Paranthropus (Paranthropus boisei) remained rather stationary near freshwater sources along the lake margins. Time-equivalent Paranthropus aethiopicus from the Eastern Rift further north in the EARS consumed a higher fraction of C4 resources, an adaptation that grew more pronounced with increasing openness of the savanna setting after 2 Ma, while Homo maintained a high versatility. However, southern African Paranthropus robustus had, similar to the Malawi Rift individuals, C3-dominated feeding strategies throughout the Early Pleistocene. Collectively, the stable isotope and faunal data presented here document that early Homo and Paranthropus were dietary opportunists and able to cope with a wide range of paleohabitats, which clearly demonstrates their high behavioral flexibility in the African Early Pleistocene.

Medieval animal management practices at Proezzhaia I: Insights from dietary stable isotope analysis

In this paper, we report the stable carbon and nitrogen isotope analysis results of wild (n = 15) and domestic (n = 21) animal samples from the Proezzhaia I site, a fortified Medieval settlement in Trans-Baikal, Siberia. Additionally, we analyzed five modern freshwater fish samples from the Shilka River, which flows immediately north of the site. Together, these samples provide the first dietary stable isotope data for the entire Trans-Baikal region. Our results reveal a C3 plant dominated diet for all animal taxa sampled, but with a possible minor inclusion of C4 plant material in the diets of some cattle (Bos sp.) and horses (Equus sp.). We infer this C4 plant was likely a type of millet, the remains of which were identified at a contemporaneous site upriver. Additionally, these results indicate that some cattle and horses consumed plant material grown in 15N-enriched soil, which suggests several distinct animal management practices, or may indicate a trade in or movement of animals from an area with a different nitrogen isotope baseline.

Stable isotopes reveal differences in diet among reed bunting subspecies that vary in bill size

Reed bunting Emberiza schoeniclus subspecies vary considerably in bill size and shape and seem to be at an early stage of speciation, in which bill might be indirectly causing reproductive isolation. Hence, we evaluated whether bill size, as well as age and sex, are associated with foraging niche in three west European subspecies of reed bunting: the thin‐billed schoeniclus, the intermediate‐billed lusitanica and the thick‐billed witherbyi. Blood sampling was undertaken at three sites in southwest Europe during the winter (when these subspecies co‐occur), and stable isotope analyses (carbon and nitrogen) were performed to assess their foraging niches. Stable isotope analyses of potential food items confirmed uniform baseline isotopic composition among sites. schoeniclus showed a significantly broader isotopic niche than lusitanica and witherbyi, which seemed otherwise similar despite the fact that witherbyi is more divergent in bill traits. Stable isotope ratios were consistent with the latter two subspecies feeding on C3‐plant‐feeding insects, whereas schoeniclus diet also included C4 plant material. Despite its lower sexual dimorphism, sex and age differences were found only in schoeniclus, but these differences vary between locations in a complex manner. Our results suggest that bill size and shape differentiated between northern, migratory and southern, resident subspecies as a consequence of natural selection through competition during the winter, which is now reflected in isotopic niche divergence between subspecies. The potential roles of sexual selection, reed thickness and summer temperature on the difference in bill size (and greater sexual dimorphism) between lusitanica and witherbyi are discussed.

Negative priming of native soil organic carbon mineralization by oilseed biochars of contrasting quality

SummaryOilseed‐derived biochar, a by‐product of pyrolysis for biodiesel production, is richer in aliphatic compounds than the commonly studied wood‐derived biochar, affecting both its mineralization in soil and its interaction with native soil organic carbon (nSOC). Here, we investigated the soil C sequestration potential of three different oilseed biochars derived from C3 plant material: soyabean, castor bean and jatropha cake. The chemical composition of these biochars was determined by elemental analysis (CHN) and 13C NMR spectroscopy. The cumulative CO2 efflux from 30‐day laboratory incubations of biochar mixed with a sandy soil containing nSOC from C4 plants was measured as a proxy for mineralization rate. The relative contribution of each source to CO2 production was calculated based on the 13C‐signatures of total CO2 efflux and the source materials (soil and biochars). Our results showed that: (i) castor bean biochar contained relatively large amounts of aliphatic compounds, resulting in a greater mineralization rate than soyabean and jatropha biochars; (ii) CO2 efflux from the soil‐biochar mixtures originated mostly from the biochars, suggesting that these biochars contain rapidly decomposable compounds; and (iii) all three oilseed biochars decelerated nSOC mineralization. This negative priming effect appeared to be caused by different factors. We conclude that oilseed biochars have the potential to increase soil C stocks directly and increase soil C sequestration indirectly in the short term through negative priming of nSOC mineralization.

Effects of substrate addition on soil respiratory carbon release under long-term warming and clipping in a tallgrass prairie.

Regulatory mechanisms of soil respiratory carbon (C) release induced by substrates (i.e., plant derived substrates) are critical for predicting ecosystem responses to climate change, but the mechanisms are not well understood. In this study, we sampled soils from a long-term field manipulative experiment and conducted a laboratory incubation to explore the role of substrate supply in regulating the differences in soil C release among the experimental treatments, including control, warming, clipping, and warming plus clipping. Three types of substrates (glucose, C3 and C4 plant materials) were added with an amount equal to 1% of soil dry weight under the four treatments. We found that the addition of all three substrates significantly stimulated soil respiratory C release in all four warming and clipping treatments. In soils without substrate addition, warming significantly stimulated soil C release but clipping decreased it. However, additions of glucose and C3 plant materials (C3 addition) offset the warming effects, whereas C4 addition still showed the warming-induced stimulation of soil C release. Our results suggest that long-term warming may inhibit microbial capacity for decomposition of C3 litter but may enhance it for decomposition of C4 litter. Such warming-induced adaptation of microbial communities may weaken the positive C-cycle feedback to warming due to increased proportion of C4 species in plant community and decreased litter quality. In contrast, clipping may weaken microbial capacity for warming-induced decomposition of C4 litter but may enhance it for C3 litter. Warming- and clipping-induced shifts in microbial metabolic capacity may be strongly associated with changes in plant species composition and could substantially influence soil C dynamics in response to global change.

Source and age of dissolved and gaseous carbon in a peatland–riparian–stream continuum: a dual isotope (14C and δ13C) analysis

Radiocarbon isotopes are increasingly being used to investigate the age and source of carbon released from peatlands. Here we use combined 14C and δ13C measurements to determine the isotopic composition of soil and soil decomposition products [dissolved organic carbon (DOC), CO2 and CH4] in a peatland–riparian–stream transect, to establish the isotopic signature and potential connectivity between carbon pools. Sampling was conducted during two time periods in 2012 to investigate processes under different temperature, hydrological and flux conditions. Isotopic differences existed in the peatland and riparian zone soil organic matter as a result of the riparian depositional formation. The peatland had a mean radiocarbon age of 551 ± 133 years BP, with age increasing with depth, and δ13C values consistent with C3 plant material as the primary source. In contrast the riparian zone had a much older radiocarbon age of 1,055 ± 107 years BP and showed no age/depth relationship; δ13C in the riparian zone was also consistent with C3 plant material. With the exception of DOC in September, soil decomposition products were predominately >100 %modern with 14C values consistent with derivation from organic matter fixed in the previous 5 years. Emissions of CO2 and CH4 from the soil surface were also modern. In contrast, CO2 and CH4 evaded from the stream surface was older (CH4: 310–537 years BP, CO2: 36 years BP to modern) and contained a more complex mix of sources combining soil organic matter and geogenic carbon. The results suggest considerable vertical transport of modern carbon to depth within the soil profile. The importance of modern recently fixed carbon and the differences between riparian and stream isotopic signatures suggests that the peatland (not the riparian zone) is the most important source of carbon to stream water.

Sources, distributions, and early diagenesis of sedimentary organic matter in the Pearl River region of the South China Sea

Suspended particles from the Pearl River, and surface sediments from the northern South China Sea (NSCS) were analyzed for elemental composition (C, N), stable carbon isotopic composition (δ13C), lignin phenols, and total hydrolyzable amino acids (THAA). Organic matter (OM) in riverine particles was depleted in 13C (avg. −28.3‰) and was derived primarily from plankton and soils, with minor contributions from C3 plant material. The δ13C of sedimentary OM became increasingly enriched in 13C (avg. −21.3‰) from the inner shelf to the slope of the NSCS, and C/N ratios decreased from the inner shelf to the slope, indicating increasing contributions of marine organic carbon (OC). Lignin phenol yields in sedimentary OM decreased from the inner shelf to the slope, indicating declining contributions of terrestrial OC. Lignin phenol compositions in riverine particles and marine sediments reflected a predominately angiosperm source. Degradation indices (DI) of sedimentary amino acids indicated increasing diagenetic alteration of marine OM with water depth and distance offshore. Increasing acid:aldehyde ratios (Ad/Al) in lignin phenols and 3,5-dihydroxybenzoic acid:vanillyl phenols (3,5-BD/V) ratios also indicated a seaward increase in the diagenetic state of terrestrial OM, presumably due to hydrodynamic sorting and biogeochemical processing. A three end-member mixing model based on lignin phenol yields and stable C isotopic compositions was used to distinguish sources of OM. Marine OM accounted for an increasing fraction (62–82%) of sedimentary OC from the inner shelf to the slope, whereas soil-derived OM accounted for a decreasing fraction (39–18%) of sedimentary OC from inner shelf to the slope. The contribution of C3 plant OM was negligible. The significant contributions of terrestrial OM in NSCS sediments are ascribed to the relatively refractory nature of soil OM and the bioavailable nature of marine OM.

Organic amendments affect δ13C signature of soil respiration and soil organic C accumulation in a long‐term field experiment in Sweden

SummaryThe contribution of young and old soil organic carbon (SOC) pools to soil CO2 fluxes and specific respiration rates of these fluxes was determined by using δ13C signatures in the Ultuna long‐term continuous soil organic matter experiment (C‐SOME). Initiated in 1956, the experiment had a range of treatments amended organically and with mineral nitrogen fertilizer under C3 cultivation until 1999, and thereafter under C4 (maize) cultivation. In 2011, soil respiration was measured in situ prior to planting, during growth and after harvest. The contributions from C4‐ and C3‐C as well as their specific respiration rates were estimated from δ13C differences in SOC and CO2 fluxes. The contributions from C4‐C sources were further separated into autotrophic and heterotrophic respiration by comparing respiration rates before and after harvest. Between 165 and 385 g C4‐C m−2 accumulated during 10 years of maize growth, contributing between 4.9 and 8.1% to the total SOC stock. Although recent C4‐C had an average specific respiration rate that was 8.4–22.6 times greater than C3‐C, total soil respiration was generally equally split between C3‐C and C4‐C. Both pools are therefore important sources of CO2 in the overall C budget, and a crucial factor in accounting for SOC stock change caused by management. Experimental treatments influenced specific respiration rates of C4 plant material and accumulation of SOC stock, demonstrating how greater SOC accumulation can be favoured by high‐quality C inputs.

Estimation of riverine carbon and organic matter source contributions using time‐based isotope mixing models

Rivers transport globally significant amounts of carbon (C) from terrestrial ecosystems to ocean margins. Understanding and quantifying the sources and respective contributions to riverine C has emerged as an important biogeochemical problem that can be approached through natural‐abundance isotope mass balance. Traditionally, the sources of riverine C have been identified either qualitatively or quantitatively through application of static mixing models. However, both source signatures and contributions can vary significantly with time. Here we apply two time‐based mixing models to a study of six rivers draining the northeast U.S. In the first model, a time‐averaged mixing model (TAMM), we vary only the source isotopic (δ13C and Δ14C) signatures. In the second model, a time‐varying mixing model (TVMM), we allow both isotopic signatures and contributions to vary with time. Based on results from the TVMM, drivers of variation in riverine particulate organic C (POC), dissolved organic C (DOC), and dissolved inorganic C (DIC) include stream discharge, stream discharge and water temperature, and water temperature and vegetation phenology, respectively. Major sources include C3plant material, algal material and slow‐turnover soil OC (“slow SOC”), which together account for 50%–100% (95% CI) of riverine POC; C3plant material and slow SOC, which together typically account for 60%–100% (95% CI) of DOC; and atmospheric exchange which alone typically accounts for 40%–60% (95% CI) of DIC. Seasonal change in relative contributions from algal material, slow SOC, and photosynthesis (in response to the identified drivers) dominates the observed variation in POC, DOC and DIC, respectively. The TVMM is a novel tool to identify component contributions under more realistic non‐static conditions, and with potential application to a broad range of biogeochemical studies.

Temporal and spatial variation in ecosystem metabolism and food web carbon transfer in a wet‐dry tropical river

Summary1. High light availability and stable base flow during the dry season promote primary production in perennial rivers of the wet–dry tropics, in contrast to production during the wet season which is often limited by turbidity and scouring. The Mitchell River of northern Queensland (Australia) was studied to understand controls on aquatic production and respiration in the dry season in relation to spatial and temporal gradients of light and temperature.2. At three sites along the river, whole‐ecosystem gross primary production (GPP) and respiration (ER) were measured from diel changes of dissolved oxygen using the open‐channel single station method. Using stable carbon and nitrogen isotope analysis, aquatic consumers and their potential basal food resources were also assessed to determine food web relationships at the beginning and end of the dry season.3. Nutrient limitation of aquatic net primary production was implied from the oligotrophic conditions and high algal C:N ratios. Rates of GPP were comparable with other tropical and temperate rivers and were regulated by light availability.4. Respiration rates were high and similar to other tropical and subtropical rivers. Up to 52% of temporal variation of ER was explained by temperature, while P/R was lowest at the downstream site.5. Benthic algae were the major carbon source for primary and secondary benthic consumers (insects) in the dry season but not for higher consumers (fish and crustaceans). Despite high rates of ER, which were probably supported by decaying terrestrial C3 plant material, this carbon source was not identified as contributing to animal consumer biomass.6. While benthic algal production in the dry season sustained benthic invertebrates, the importance of external subsidies of carbon along the river, probably from the floodplain, was emphasised for fish and large invertebrates, which evidently were feeding on carbon sources not present in channel waterholes during the dry season.

Trophic importance of a temperate intertidal wetland to resident and itinerant taxa: evidence from multiple stable isotope analyses

Juveniles of commercially important fish species congregate in shallow vegetated estuarine habitats during high tides. Considerable debate has centred on whether the significance of these habitats lies in their provision of greater feeding opportunities, or shelter from predation afforded by greater structural complexity. We tested the hypothesis that an inundated mangrove and saltmarsh wetland provided feeding opportunities for itinerant species, and that the contribution of wetland primary producers and grazing herbivores could be identified in their diet, using stable isotopes of carbon and nitrogen. Potential sources of dietary carbon included mangrove, saltmarsh, seagrass, seagrass epiphytic material and benthic organic material. Saltmarsh plants (mostly Sporobolus virginicus and Juncus kraussii) and fine benthic organic material appeared to be the primary sources of dietary carbon for the resident grazing herbivores in the wetlands, based on IsoSource mixing models. During high tide, species of itinerant fish enter the mangrove and, when inundated, the saltmarsh, and feed primarily on crab larvae and copepods. Fine benthic organic matter, seagrass epiphyte, and C3 and C4 plant materials also supplement the diet of some fish. The crab larvae therefore provide a significant source of nutrition and an important link between the intertidal wetlands and the adjacent estuarine ecosystem. The carnivorous fish Acanthopagrus australis, at the highest trophic level, hunted within or adjacent to the mangrove–saltmarsh wetland and fed on several lower-order consumers within the wetland. The present study highlights the significance of mangrove and saltmarsh wetlands as a feeding habitat for resident grazers and itinerant nekton.

Experimental Study on the Origin of Cremated Bone Apatite Carbon

Bones that have undergone burning at high temperatures (i.e. cremation) no longer contain organic carbon. Lanting et al. (2001) proposed that some of the original structural carbonate, formed during bioapatite formation, survives. This view is based on paired radiocarbon dating of cremated bone apatite and contemporary charcoal. However, stable carbon isotope composition of carbonate in cremated bones is consistently light compared to the untreated material and is closer to the δ13C values seen in C3 plant material. This raises the question of the origin of carbonate carbon in cremated bone apatite. That is, does the isotope signal reflect an exchange of carbon with the local cremation atmosphere and thus with carbon from the burning fuel, or is it caused by isotopic fractionation during cremation?To study the changes in carbon isotopes (14C, 13C) of bone apatite during burning up to 800 °, a modern bovine bone was exposed to a continuous flow of an artificial atmosphere (basically a high-purity O2/N2 gas mix) under defined conditions (temperature, gas composition). To simulate the influence of the fuel carbon available under real cremation conditions, fossil CO2 was added at different concentrations. To yield cremated bone apatite properties similar to archaeological cremated bones, in terms of crystallographic criteria, water vapor had to be added to the atmosphere in the oven. Infrared vibrational spectra reveal large increases in crystal size and loss of carbonate upon cremation. The isotope results indicate an effective carbon exchange between bone apatite carbonate and CO2 in the combustion gases depending on temperature and CO2 concentration. 14C dates on archaeological cremated bone apatite may thus suffer from an old-wood effect. Paired 13C and 14C values indicate that in addition to this exchange, isotope fractionation between CO2 and carbonate, and admixture of carbon from other sources such as possibly collagen or atmospheric CO2, may play a role in determining the final composition of the apatite carbonate.

Sources of organic carbon and depositional environment in the Bengal delta plain sediments during the Holocene period

This study investigated the sources of organic matter and sediment depositional environment within fluviatile sediments of the Ganges–Meghna (GM) delta plains. The very low contents of trace metals e.g., chromium (Cr), cobalt (Co), scandium (Sc), and vanadium (V), organic carbon content, and cerium (Ce)-anomaly data of sediments indicate the redox conditions that fall within the boundary of oxic–anoxic condition, with dominantly oxic conditions in the sediment deposition environment. The higher atomic carbon nitrogen (C/N)a ratios and depleted stable carbon isotope ratio (δ13C) values for sediments from three study areas indicated the terrestrial sources of organic matter derived from C3 plant materials, whereas the contribution of organic materials from C4 vegetation and riverine productivity is low. Some silty sand samples exhibited lower (C/N)a ratios and enriched δ13C values in Sonargaon and Faridpur areas that are attributed to the adsorption of ammonium ions on clay minerals and the contribution of organic matter from C4 plants. Total sulfur over total organic carbon (TS/TOC) ratios in sediments of the Ganges delta reflect the nonmarine environments of sediment deposition. The lower ratios of syringyl to vanillyl phenols (S/V), cinnamyl to vanillyl phenols (C/V), and acid to aldehyde in vanillyl phenols (Ad/Al)v observed in Daudkandi indicate that the lignin in sediments derived from dominant woody gymnosperm sources and is very highly degraded. By contrast, the S/V ratio, C/V ratios, and [Ad/Al]v ratios in Faridpur suggest that the lignin in sediments derived from a mixture of woody and nonwoody angiosperm plant tissue contribution that underwent high degradation as well.

Mechanisms of short-term soil carbon storage in experimental grasslands

We investigated the fate of root and litter derived carbon in soil organic matter and dissolved organic matter in soil profiles, in order to explain mechanisms of short-term soil carbon storage. A time series of soil and soil solution samples was investigated at the field site of The Jena Experiment between 2002 and 2004. In addition to the main experiment with C3 plants, a C4 species ( Amaranthus retroflexus L.) naturally labeled with 13C was grown on an extra plot. Changes in organic carbon concentration in soil and soil solution were combined with stable isotope measurements to follow the fate of plant carbon into the soil and soil solution. A split plot design with plant litter removal versus double litter input simulated differences in biomass input. After 2 years, the no litter and double litter treatment, respectively, showed an increase of 381 g C m −2 and 263 g C m −2 to 20 cm depth, while 71 g C m −2 and 393 g C m −2 were lost between 20 and 30 cm depth. The isotopic label in the top 5 cm indicated that 115 g C m −2 and 156 g C m −2 of soil organic carbon were derived from C4 plant material on the no litter and the double litter treatment, respectively. Without litter, this equals the total amount of 97 g C m −2 that was newly stored in the same soil depth, whereas with double litter this clearly exceeded the stored amount of 75 g C m −2. Our results indicate that litter input resulted in lower carbon storage and larger carbon losses and consequently accelerated turnover of soil organic carbon. Isotopic evidence showed that inherited soil organic carbon was replaced by fresh plant carbon near the soil surface. Our results suggest that primarily carbon released from soil organic matter, not newly introduced plant organic matter, was transported in the soil solution. However, the total flow of dissolved organic carbon was not sufficient to explain the observed carbon storage in deeper soil layers, and the existence of additional carbon uptake mechanisms is discussed.

Isolation of bicarbonate from equine urine for isotope ratio mass spectrometry†

Sodium bicarbonate administration to horses prior to competition in order to enhance the buffer capacity of the organism is considered as a doping offence. The analysis of the isotopic composition of urinary bicarbonate/CO2 (TCO2) may help to identify an exogenous bicarbonate source, as technical sodium bicarbonate exhibits elevated δ13C values compared with urinary total carbon. The isolation of TCO2 from 60 equine urine samples as BaCO3 followed by an isotopic analysis shows a significant variability of δ13C for TCO2 of more than 10 ‰. The δ13C of total carbon and TCO2 seem to reflect different proportions of C3 and C4 plant material in the diet. The isotopic analysis of different mixtures of technical NaHCO3 and equine urine shows that TCO2 can be easily isolated without major isotopic fractionation; however, attention has to be paid to the storage time of urine samples, as a shift of δ13C of TCO2 to lower values may occur. †Revised version of the paper presented at the 27th Annual Meeting of the German Association for Stable Isotope Research (GASIR), 4–6 October 2006, Freiberg, Germany.

Isotope and lignin signatures in tropical peat core (Rawa Danau, Indonesia): An approach to reconstruct past vegetation and climate changes

Peat samples from a 3.60 m core collected from Rawa Danau, West Java, Indonesia, were studied to reconstruct past vegetation and climate changes. The study carried out combining visual observations, elemental analyses, stable carbon and nitrogen isotope analyses as well as CuO oxidation of lignin residues. Variations of total organic carbon (TOC: 55.53-3.18 %, mean 23.31 %), total nitrogen (TN: 2.52-0.06 %, mean 0.94 %) and water content (WC: 46.8-93.2 %, mean 79.0 %) with core lithology reflected dry and wet cycles. Vertical profiles for TOC, TN, WC and core lithology also had signatures of heavy precipitations and consequent land sliding at the abrupt change of climate (wet cycles). Variations of (C/N)a (15-93, mean 27) and δ13C (-27.0 to -30.1 ‰, mean -28.5 ‰) of organic matter (OM) in the peat core indicated that the organic material was comprised of terrestrial C3 plant material. The direct input of aquatic plant matter was small or overwhelmed by high terrestrial input, although changes in lake productivity due to decreasing/increasing nutrient availability were reflected in δ15N profile. At low elevations in the tropical area, a large shift in vegetation zones was not likely observed. Most species might persist at the site when small-scale localized environmental changes and human disturbances or natural forest fires occurred, but the abundances of particular species might change, depending on the natural conditions in which a species could grow. However, vegetation changes associated with periodical sequence of dry and wet microenvironment were inferred from the total lignin phenol (TLP) profile.

δ 13C and δD identification of sources of lipid biomarkers in sediments of Lake Haruna (Japan)

Organic materials in lacustrine sediments are from multiple terrestrial and aquatic sources. In this study, carbon (δ 13C) and hydrogen isotopic compositions (δD) of phytol, various sterols, and major n-fatty acids in sediments at Lake Haruna, Japan, were determined in their solvent-extractable (free) and saponification-released forms (bound). The δ 13C-δD distributions of these lipid molecules in sediments are compared with those of terrestrial C3 and C4 plants, aquatic C3 plants, and plankton to evaluate their relative contributions. δ 13C-δD of free phytol in sediments is very close to that of phytol in plankton samples, whereas δ 13C-δD of bound phytol in sediments is on a mixing line between terrestrial C3 plant and plankton material. Unlike phytol, no significant δ 13C-δD difference between free and bound forms was found in sterols and n-fatty acids. δ 13C-δD values of algal sterols such as 24-methylcholesta-5,22-dien-3β-ol in sediments are close to those of plankton, whereas δ 13C-δD of multiple-source sterols such as 24-ethylcholest-5-en-3β-ol and of major n-fatty acids such as n-hexadecanoic acid in sediments are between those of terrestrial C3 plants and plankton samples. Thus, δ 13C-δD distributions clearly indicate the specific source contributions of biomarkers preserved in a lacustrine environment. Free phytol and algal sterols can be attributed to phytoplankton, and bound phytol, multiple source sterols, and major n-fatty acids are contributed by both terrestrial C3 plants and phytoplankton.