δ13C Values Of Plants Research Articles

Influence of provenance and preservation on the carbon isotope variations of dispersed organic matter in ancient floodplain sediments

Carbon isotope ratios of bulk organic matter in sedimentary rocks (δ13CDOM) are a potential source of paleoenvironmental information in terrestrial stratigraphic sequences. However, insufficient understanding of the range of depositional and post‐depositional controls on δ13CDOM values makes interpretations of these data difficult. Here we evaluate the effects of organic matter (OM) provenance and preservation on δ13CDOM using records spanning the Paleocene Eocene Thermal Maximum (PETM) in the Bighorn Basin (Wyoming, USA) as a case study. We sampled sedimentary rocks spanning the PETM in two well‐studied locations—Polecat Bench (PB) and Highway 16 (HW16)—in the Bighorn Basin. Independent carbon isotope records from biomarkers and pedogenic carbonates at these sites suggest that local shifts in plant and soil δ13C values associated with the PETM CIE were broadly similar and were characterized by an abrupt ∼5‰ decrease followed by a plateau and a eventual return to pre‐PETM δ13C values. The δ13CDOM records from both sites differ significantly from these reference curves in both amplitude of change and in preserving high‐frequency isotopic fluctuations and large isotopic anomalies superimposed on the general pattern of isotopic change through the CIE. For each location, we separated organo‐mineral fractions (MOM), concentrated macerals from 20 stratigraphic levels and analyzed the carbon isotope ratio (δ13C) of each fraction. At both sites the δ13C of the fine and coarse MOM differ significantly from each other and from δ13CDOM. Concentration‐weighted mixing of these isotopically distinct OM fractions explains high resolution δ13CDOM fluctuations but does not explain the large isotopic anomalies observed at both sites. At HW16, we identified two thermally and isotopically distinct populations of macerals interpreted as being indigenous and recycled OM. At this site, one over total organic carbon (1/TOC) values correlate with δ13CDOM for pre‐PETM and PETM strata and both relationships converge toward the δ13C of recycled OM for low TOC. At PB, macerals display homogeneous thermal maturity, but the proportion of isotopically distinct vitrinite and liptinite varies between facies. Relationships between 1/TOC and δ13CDOM are also present within specific stratigraphic intervals at PB, but values do not converge on a single isotopic value across the sampled interval. These observations are consistent with variable mixing of OM fractions having different provenance—mixing of exotic recycled OM at HW16 and locally reworked OM at PB with indigenous “fresh” OM at both sites—and explain the large anomalies observed in the δ13CDOM records at both sites. Our findings raise questions about the assumption that OM in ancient sediments is indigenous and dominantly records δ13C variations of local plants.

Late Miocene climatic and environmental variations in northern Greece inferred from stable isotope compositions (δ18O, δ13C) of equid teeth apatite

During the late Miocene Vallesian–Turolian transition, an important faunal turnover affected continental vertebrate faunas, and particularly primates with the replacement of hominids by cercopithecid monkeys in Europe. In order to better understand this turnover from a climatic perspective, stable oxygen and carbon isotope compositions of fossil equid tooth enamel contemporaneous with either hominids or cercopithecids have been analyzed. Hipparion teeth recovered from seven Greek localities spanning from the late Vallesian to the end of Turolian have δ18Op values of apatite phosphate suggesting an increase in mean air temperatures from 13±3°C at the beginning of the Vallesian to 17±2°C during the late Turolian. δ13C values of local plants have been estimated using the carbon isotope compositions of apatite carbonate. By applying to our data the relationship established between the δ13C value of modern C3 plants and mean annual precipitations, estimated average precipitations slightly decreased from 890 (+109−100) mma−1 to 471 (+58−54) mma−1 during this time span. According to Köppen's classification of climates, northern Greece was submitted to modern-like Mediterranean climates during the late Miocene. The change in climatic conditions, which took place during the late Vallesian–early Turolian transition, remained within the range of Mediterranean climate modes, thus being unlikely at the origin of a dramatic modification in local vegetation. This study strongly suggests that climate might not be the key factor of the Vallesian–Turolian major faunal turnover at least in the Eastern Mediterranean Basin.

Geochemical and Isotopic Signatures of Surficial Sediments from the Western Continental Shelf of India: Inferring Provenance, Weathering, and the Nature of Organic Matter

Abstract Bottom sediments from thirteen transects sampled mainly at depth contours of 30, 100, and 200 m along the western continental margin of India, falling in two offshore sectors from Dwaraka to Goa and Cape Comorin to Goa, were analyzed for calcium carbonate, major elements in silicate fraction, trace and rare earth elements in the bulk fraction, and carbon and nitrogen isotopes in organic matter to understand the provenance of sediments, weathering patterns in the source areas, and nature of organic matter. Major elements such as Si, Ti, Mg, and discrimination plots involving alkalies and silica have shown a distinct north–south provinciality, with the source signatures pointing at Deccan basalt for sediments in the north (from Dwaraka to Goa) and gneisses and granulites of South India in the south. Shale-normalized REE patterns and REE content suggest additional local sources mainly in the southwest coast of India. Degree of alteration determined using Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA), and A-CN-K plots have suggested that the sediments are moderately weathered despite the intense orographic rainfall in the source area. Variability in degree of chemical weathering is seen with the change in provenance. In general, the sediments north of Goa with a provenance of Deccan basalts show a higher chemical weathering index. Corg/N molar ratios are mostly between 10 and 12 (minimum and maximum being 6.9 and 14 respectively), which are closer to values for marine organic matter. This is corroborated by marine δ13C values (−18.2 to −21.6‰). While they broadly fall within the marine values, heavier values are seen in northern transects off Porbandar and Dwaraka, where the sediments have a provenance different from those in the south. This could be due to a higher contribution from C4-type vegetation in the north, consistent with heavier δ13C values in terrestrial plants in source regions. Heavier δ15N values are observed for the northern transects (north of Ratnagiri), which is supported by the intense denitrification in the northern Arabian Sea.

Evaluation of paleoclimatic conditions east and west of the southern Canadian Cordillera in the mid-late Paleocene using bulk organic δ13C records

Carbon isotope records from organic matter provide a key data set for constraining past fluctuations in the isotopic composition of atmospheric carbon dioxide (δ13Catm), hydrologic conditions, and plant community composition. Here we evaluate spatiotemporal shifts in these three conditions using δ13C values of bulk organic carbon (δ13Cbulk) from Paleocene strata in northwest Washington, U.S.A. and west-central Alberta, Canada. Our data set contains 352 analyses from the Chuckanut and Paskapoo formations. Mean δ13Cbulk values in the two areas are statistically indistinguishable (−24.5‰ and −24.4‰ (VPDB), respectively), and exhibit a wide range of values (~5–7‰). In both areas sequential vertical samples show large fluctuations in δ13Cbulk values, on average of ~1.0‰±1.0 (1σ). There are no distinct up-section trends or structured excursions in the ~850meter stratigraphic section in the Chuckanut Formation nor the ~125meter section in the Paskapoo Formation. Furthermore, δ13Cbulk values are independent of the weight percent organic carbon (%C) and lithology of the sample.The lack of a systematic relationship and correlation between δ13Cbulk and %C values indicates isotopic fractionation during post-mortem processes, such as microbial respiration, exerted minimal influence on the isotopic patterns. The independence of δ13Cbulk values from lithology suggests variability is unrelated to local spatial gradients in vegetation community and water availability across the paleo-landscape. However, the wide range and large fluctuations in δ13Cbulk values is similar to stochastic intra-site variability of plant δ13C values within modern settings. The absence of structured, up-section trends indicates minimal secular variation in the carbon isotopic composition of atmospheric CO2, rainfall, and plant community composition. Moreover, we show that a previous carbon isotope excursion ascribed to the Paleocene–Eocene Thermal Maximum in the Paskapoo Formation is actually a result of aliasing related to sampling density. Finally, the statistically indistinguishable mean δ13Cbulk values in the two regions imply similarly wet and humid climatic conditions when combined with sedimentologic and paleobotanical data. The records support early Paleogene circulation models that show strong orographic precipitation patterns in the Pacific Northwest associated with incipient extensional tectonics in the region and enhanced transport of moisture-laden polar air masses southward into the Canadian continental interior.

Variations in carbon isotope ratios of plants across a temperature gradient along the 400 mm isoline of mean annual precipitation in north China and their relevance to paleovegetation reconstruction

Carbon isotope values (δ13C) of plants reflect the balance between photosynthesis and stomatal conductance and vary with environmental conditions. Temperature is an important influential factor for plant δ13C; however, variations of plant δ13C across temperature gradients have yet to be quantified. This impedes interpretation of variability of δ13C in ancient terrestrial organic matter and reconstructions of paleoclimate and paleoecology. In this study, the effect of temperature on δ13C of C3 and C4 plants was assessed by comprehensive investigation of a large number of species (118 C3 plants and 17 C4 plants) from 29 sites across a temperature gradient along the 400 mm mean annual precipitation isoline in north China. After deducting the effects of precipitation on plant δ13C, a strong positive relationship is found between δ13C values of C3 plants averaged for each site and mean annual temperature, with a coefficient of 0.104‰/°C; however, no significant correlation is found for C4 plants. Based on our results, we conduct a sample reconstruction of paleovegetation of the central Chinese Loess Plateau and demonstrate that, to a certain extent, our paleovegetation reconstruction is affected by temperature corrections.

Maize, beans and the floral isotopic diversity of highland Oaxaca, Mexico

Oaxaca, Mexico has been inhabited by humans for over 10,000 years. From the time of earliest habitation, this environment provided a wide floral subsistence to its human inhabitants, notably documented at the cave site of Guila Naquitz. Light stable isotopes, primarily carbon and nitrogen, have been used in dietary and environmental reconstructions throughout Mexico and Central America. We report a large isotopic study of wild and market plants from Oaxaca that demonstrates 1) overlapping δ13C values of C4 plants, including maize, and plants that utilize the Crassulacean Acid Metabolism (CAM) pathway for biosynthesis, 2) the existence of a significant C4 grass biomass, 3) the lack of isotopic separation in the δ15N of legumes and non-leguminous plants and 4) the increase in the nitrogen isotopic composition of crop plants relative to wild plant averages. These four observations are potential complicating factors in interpretations involving the origins and spread of maize agriculture, the relative amount of maize in the diet and assessments of trophic level or meat contributions to the human diet.

Stable isotope biogeochemistry of seabird guano fertilization: results from growth chamber studies with maize (Zea mays).

BackgroundStable isotope analysis is being utilized with increasing regularity to examine a wide range of issues (diet, habitat use, migration) in ecology, geology, archaeology, and related disciplines. A crucial component to these studies is a thorough understanding of the range and causes of baseline isotopic variation, which is relatively poorly understood for nitrogen (δ15N). Animal excrement is known to impact plant δ15N values, but the effects of seabird guano have not been systematically studied from an agricultural or horticultural standpoint.Methodology/Principal FindingsThis paper presents isotopic (δ13C and δ15N) and vital data for maize (Zea mays) fertilized with Peruvian seabird guano under controlled conditions. The level of 15N enrichment in fertilized plants is very large, with δ15N values ranging between 25.5 and 44.7‰ depending on the tissue and amount of fertilizer applied; comparatively, control plant δ15N values ranged between −0.3 and 5.7‰. Intraplant and temporal variability in δ15N values were large, particularly for the guano-fertilized plants, which can be attributed to changes in the availability of guano-derived N over time, and the reliance of stored vs. absorbed N. Plant δ13C values were not significantly impacted by guano fertilization. High concentrations of seabird guano inhibited maize germination and maize growth. Moreover, high levels of seabird guano greatly impacted the N metabolism of the plants, resulting in significantly higher tissue N content, particularly in the stalk.Conclusions/SignificanceThe results presented in this study demonstrate the very large impact of seabird guano on maize δ15N values. The use of seabird guano as a fertilizer can thus be traced using stable isotope analysis in food chemistry applications (certification of organic inputs). Furthermore, the fertilization of maize with seabird guano creates an isotopic signature very similar to a high-trophic level marine resource, which must be considered when interpreting isotopic data from archaeological material.

Carbon isotopic composition (δ13C and 14C activity) of plant samples in the vicinity of the Slovene nuclear power plant

δ13C values of various plants (apples, wheat, and maize) collected in the vicinity of the Krško Nuclear Power Plant (Slovenia) during 2008 and 2009 were determined. By measuring dried samples and their carbonized counterparts we showed that no significant isotopic fractionation occurs during the carbonization phase of the sample preparation process in the laboratory. The measured δ13C values of the plants were used for δ13C correction of their measured 14C activities.

Impacts of environmental deterioration on the carbon isotope values of modern vegetation and gazelles in the southern Levant: Predicting the severity of the Younger Dryas

This study uses the carbon isotope values (δ13C) to determine how environmental deterioration is expressed in the δ13C values of vegetation and gazelles in the southern Levant. The ultimate goal is to use these modern data to predict the climatic impact of the Younger Dryas (YD). Climatic deterioration associated with the YD has been cited as the trigger for the transition to agriculture in the southern Levant. However, the evidence for the local severity of this climatic event is equivocal. There is disagreement over whether Mediterranean forest was succeeded by arid adapted steppic plant communities in what has been termed the Natufian ‘core area’. The modern data show a moderately negative regression slope between aridity and the δ13C values of both modern C3 plants and gazelle horn keratin within the Mediterranean phytogeographic belt. This pattern is expressed in both seasonal and annual datasets. The incorporation of a C4 plant component into gazelle diets is evident in the arid Mediterranean region, and is more pronounced in the dry season. The latter is apparent even despite interference caused by gazelle foraging on cultivated land. Based on the present day data, it is predicted that the succession of Mediterranean forest by open steppic vegetation would cause a positive shift of >2‰ in the δ13C values of C3 plants and gazelles. The argument is based on the response of C3 vegetation to growth under increasing water stress conditions and the current distribution of C3 and C4 vegetation in relation to rainfall. This study presents a new tool with the potential to assess the climatic severity of the YD and its effect on Natufian foraging strategies.

Physiological ecology of mycoheterotrophy

Physiological ecology of mycoheterotrophy

Autochthonous and allochthonous plant contributions to coastal benthic detritus deposits: a dual-stable isotope study in a volcanic lake

The high numbers of primary producers represent multiple sources of organic matter accumulating onto lake bottoms. The difficulty of distinguishing the relative contribution to the mixture presents considerable challenges to the analysis of these organic deposits. In this study, dual-stable isotope analysis and IsoSource model were used to identify allochthonous and autochthonous components of detritus deposits (Particulate Organic Matter: POM) at two different bottom slope sites of a volcanic lake (lake Bracciano). Experiments were carried out to calibrate IsoSource on constructed plant mixtures and assess changes in isotope ratios during plant decomposition. IsoSource satisfactorily discriminated the constructed mixture sources with a few exceptions. Changes in isotopic enrichment during decomposition were low, and thus did not represent a confounding variable in the isotopic analysis. By contrast, chemical and geological differences of the study sites were associated with differences in plant δ13C and δ15N values (more than 2‰ within single plant species). At both sites, the isotopic signals of POM fell between polygons delineated by source end members with an evident shift of δ13C toward allochthonous sources. POM amount and diversity were greater at the flatter bottom site, where allochthonous contributions were larger than at the other site. In particular, IsoSource ranked species contributions as follows: A. glutinosa > P. australis > A. donax > S. alba > P. nigra > the benthic macroalga Chara sp. at the first site, and A. glutinosa > P. nigra > the aquatic macrophyte C. demersum at the latter. The composition of littoral POM was determined by allochthonous sources in proportion to their relative abundances (as percent land cover) with differences between sites due to bottom slope.

δ13C difference between plants and soil organic matter along the eastern slope of Mount Gongga

Carbon isotope ratios (δ13C) of plants, litter and soil organic matter (0–5 cm, 5–10 cm and 10–20 cm) on the eastern slope of Mount Gongga were measured. The results show that δ13C values of plants, litter and soil organic matter all decrease first and then increase with altitude, i.e. δ13C values gradually decrease from 1200 to 2100 m a.s.l., and increase from 2100 to 4500 m a.s.l. The δ13C altitudinal variations are related to the distribution of C3 and C4 plants on the eastern slope of Mount Gongga, because C4 plants are observed to grow only below 2100 m, while C3 plants occur at all altitudes. There are significantly positive correlations among δ13C of vegetation, δ13C of litter and δ13C of soil organic matter, and litter, 0–5 cm, 5–10 cm and 10–20 cm soil organic matter are 0.56‰, 2.87‰, 3.04‰ and 3.49‰ greater in δ13C than vegetation, respectively. Considering the influences of rising concentration of atmospheric CO2 and decreasing δ13C of atmospheric CO2 since the industry revolution on δ13C of plants, 1.57‰ is proposed to be the smallest correction value for reconstruction of paleovegetation using δ13C of soil organic matter.

Is it better to give than to receive? A stable isotope perspective on orchid–fungal carbon transport in the green orchid species Goodyera repens and Goodyera oblongifolia

Is it better to give than to receive? A stable isotope perspective on orchid–fungal carbon transport in the green orchid species <i>Goodyera repens </i>and<i> Goodyera oblongifolia</i>

Comparisons in water relations of plants between newly formed riparian and non-riparian habitats along the bank of Three Gorges Reservoir, China

The water table in the Three Gorges Reservoir (TGR) rose significantly since the construction of the Three Gorges Dam across the Yangtze River. Little is known about how such a change in local hydrological condition will affect the ecophysiology of plants along the bank of the world’s largest reservoir. In this study, water relations of the dominant plants were investigated over an entire year period by comparing stable isotope compositions of xylem water, leaf water potentials and foliar carbon isotope ratios at a newly-formed riparian site near the river bank and two non-riparian sites at higher elevations. The isotopic compositions of xylem water indicated that the plants in the newly-formed riparian zone acquired water mainly from the soil previously infiltrated by local rain rather than the Yangtze River water. Predawn and midday water potentials of the riparian trees were also similar to those at the non-riparian sites. Leaf δ13C values of plants across the three sites also showed no difference, even though there was a significant difference among species. Our results indicate that plants at the newly formed transient riparian area along the bank of TGR do not depend on the Yangtze River water for their water sources and that rising water levels in this reservoir may not lead to immediate changes in water relations of the plants along the bank.

Carbon isotope ratios of C4 plants in loess areas of North China

Carbon isotope ratios (δ13C) of 89 C4 plant samples were determined from the loess area in North China. δ13C values vary between −10.5‰ and −14.6‰ with a mean of −12.6‰. Along a precipitation gradient from the semi-moist area to the semiarid area, then to the arid area, the δ13C values of C4 plants show a slight decreasing trend. The δ13C values of C4 plants in the dry season are found lower than those in the wet season. These trends are opposite to those observed for C3 species.

δ13C variation of C3 and C4 plants across an Asian monsoon rainfall gradient in arid northwestern China

AbstractWe have investigated carbon isotopic compositions of four plant genus/species, Bothriochloa ischaemum (C4), Stipa bungeana (C3), Lespedeza sp. (C3) and Heteropappus less (C3), along a precipitation gradient in northwest China in order to assess the impact of water availability on the carbon isotopic discrimination against 13C during carbon assimilation in this area. This information is necessary for reconstruction of paleovegetation, particularly paleo‐C3/C4 plant ratios using δ13C value of organic matter in loess and paleosols in the Chinese Loess Plateau. The δ13C of C3 plants, as a group, exhibits a negative correlation with the annual precipitation amount with a total change and sensitivity of 5‰ and −1.1‰/100 mm, respectively, for the precipitation range from 200 to 700 mm. The C4 grass, B. ischaemum responds to aridity by decreasing 1.7‰ for over the precipitation range from 350 to 700 mm; the plant δ13C is significantly correlated with annual precipitation with a slope −0.61‰/100 mm. This result implies that without considering the effect of water availability on the plant δ13C values, reconstruction of percent C4 vegetation during the last glaciation can be overestimated by about a factor of two.

The carbon isotope composition of C3 herbaceous plants in loess area of northern China

13C of 367 C3 herbaceous plants was measured in loess area in northern China. Their δ13C values vary between −21.7%. and −30.0%., with a mean of −26.7%.. In the center of Loess Plateau (semimoist area) with annual precipitation of 400–600 mm, the δ13C values of C3 herbaceous plants range from −24.4%. to −28.5%., with a mean of −27.5%.. In the west of Loess Plateau (semiarid and arid area) with annual precipitation less than 400 mm, they range between −21.7%. and −30.0%., with a mean of −26.2%.. Annual precipitation is the main factor that makes δ13C values of C3 herbaceous plants in the west greater than those in the central Loess Plateau. The composition of δ13C in C3 plants increases with deceasing annual precipitation, and the mean change is −49%./100 mm.

How closely do the delta(13)C values of Crassulacean Acid metabolism plants reflect the proportion of CO(2) fixed during day and night?

The extent to which Crassulacean acid metabolism (CAM) plant delta(13)C values provide an index of the proportions of CO(2) fixed during daytime and nighttime was assessed. Shoots of seven CAM species (Aloe vera, Hylocereus monocanthus, Kalanchoe beharensis, Kalanchoe daigremontiana, Kalanchoe pinnata, Vanilla pauciflora, and Xerosicyos danguyi) and two C(3) species (teak [Tectona grandis] and Clusia sp.) were grown in a cuvette, and net CO(2) exchange was monitored for up to 51 d. In species exhibiting net dark CO(2) fixation, between 14% and 73.3% of the carbon gain occurred in the dark. delta(13)C values of tissues formed inside the cuvette ranged between -28.7 per thousand and -11.6 per thousand, and correlated linearly with the percentages of carbon gained in the light and in the dark. The delta(13)C values for new biomass obtained solely during the dark and light were estimated as -8.7 per thousand and -26.9 per thousand, respectively. For each 10% contribution of dark CO(2) fixation integrated over the entire experiment, the delta(13)C content of the tissue was, thus, approximately 1.8 per thousand less negative. Extrapolation of the observations to plants previously surveyed under natural conditions suggests that the most commonly expressed version of CAM in the field, "the typical CAM plant," involves plants that gain about 71% to 77% of their carbon by dark fixation, and that the isotopic signals of plants that obtain one-third or less of their carbon in the dark may be confused with C(3) plants when identified on the basis of carbon isotope content alone.

Biogeochemical properties of a tropical swamp forest ecosystem in southern Thailand

The distributions of organic matter in the tropical swamps in southern Thailand are reported. The concentrations of particulate and dissolved organic carbon (POC and DOC) in the Bang Nara River, which drains swamp forests and nearby paddy fields, were 2.9 ± 2.0 and 6.2 ± 1.3 mg C l−1, respectively. Although the variation was large, DOC concentration in the Bang Nara River seemed to be higher than POC in November 1992 (DOC/POC ratio, 2.8 ± 2.2). River waters from the upland areas were characterized by low POC and DOC concentrations as compared with Bang Nara River water. The δ13C values of POC and river sediments were useful to distinguish between organic matter originating in upland and swamp areas. It is suggested that the distributions of organic matter and its isotopic composition reflect the difference in drainage characteristics between lowland swamp and upland areas. Isotopic analyses of plant leaves and soils revealed that the swamp forest ecosystems were characterized by low δ13C and low δ15N values, which suggested low efficiency of water use by plants and large contributions of atmospheric deposition of nitrogen, respectively. Although CO2 recycling in the forest might be an important factor determining the δ13C values of understory plants, the main process in carbon metabolism of tropical swamp forests would be CO2 exchange between the atmosphere and forest canopy.

Stable carbon and nitrogen isotopic characterization of organic matter in a mangrove ecosystem on the southwestern coast of Thailand

Organic matter in a tropical mangrove ecosystem was characterized by stable carbon and nitrogen isotopic analyze, conducted on various organic samples, including land and mangrove plants, soils, particulate organic matter (POM), and sea and river sediments along the southwestern coast of Thailand. The δ13C values of land plants and POM in river water can be explained in terms of a greater influence of C3 plants than C4 plants in this area. The POM and sediments from the Trang River and Ko Talibong area showed systematically higher δ15N values than those from Ko Muk and other coastal areas. Organic matter in the Trang River might be influenced by nitrogen released from agricultural or human waste, which could affect the isotopic composition of POM and sediments in the Trang River estuary and along the coast near the river mouth. We used a stochastic method to estimate the contributions of four organic end-members, identifiable by their δ13C and δ15N values. The results implied that seagrasses were a major source of sedimentary organic matter, contributing 42 ± 5% in the Ko Muk area and 36 ± 5% in the Ko Talibong area. The contribution of coastal POM to sediments was estimated to be only 13% in Ko Muk and 19% in Ko Talibong. Mangrove plants contributed approximately 23% in both areas. It was concluded that seagrasses are an important source of sedimentary organic matter in this coastal region of southwestern Thailand.