Carbon Isotope Composition Of Plants Research Articles

Variation in carbon isotope composition of plants across an aridity gradient on the Loess Plateau, China

Carbon isotope composition (indicated by leaf δ13C) reflects plants' strategies to balance carbon acquisition and water loss, which is directly linked to water use efficiency. At a large scale, leaf δ13C has been demonstrated to be closely related to climate and plant functional types; however, at a regional scale, its variation across an aridity gradient and species categories and its covariation with traits in leaf economic spectrum (LES) traits are still unclear. Here, a multivariate statistical analysis was carried out with 271 observations of leaf δ13C from 22 sampling sites on the Loess Plateau. Our results showed that (1) mean leaf δ13C did not differ significantly among life forms in C3 plants, with the maximum mean values occurring in geophytes (−26.31‰) and the minimum values occurring in lianas (−28.29‰); (2) the leaf δ13C responses of different life forms, families and species categories to climates were consistent for C3 plants, namely, they presented similar response rates to changes along the aridity gradient (represented by the moisture index); (3) climate, soil, species category, and leaf economic spectrum traits jointly explained 78.4% of the variation in leaf δ13C for C3 plants. Species category was the largest determinant of leaf δ13C variations for both C3 and C4 plants. Revealing the variation in leaf δ13C of the Loess Plateau plants not only helps us to understand plant adaptation strategies under arid conditions but also provides scientific support for ecological management in vegetation restoration regions.

Climate in the Western Cordillera of the Central Andes over the last 4300 years

The Distichia peat core obtained in the Carhuasanta valley near Nevado Mismi, Cordillera Chila, provides information on climatic and environmental conditions over the last ∼4300 years. The relative changes in the stable carbon isotope composition of plant remains preserved in the core reflect major temperature fluctuations in the Western Cordillera of the southern Peruvian Andes. These temperature variations can be additionally linked with the changes in precipitation patterns by analysing C% and C/N ratio in the core. Relatively warm and moist conditions prevailed from 4280 to 3040 cal. yrs BP (BC 2330–1090) with a short colder dry episode around 3850 cal. yrs BP (BC 1900). The most prominent climate changes recorded in the peat occurred between 3040 and 2750 cal. yrs BP (BC 1090–800) when the initial warming turned to a rapid cooling to temperatures at least 2 °C lower than the mean for the Late Holocene. Initially drier conditions within this event turned to a short wet phase after 2780 cal. yrs BP (BC 830) when the temperature increased again. This event coincides with significant changes in peat and ice core records in the Central Andes matching the timing of the global climate event around 2.8 cal. ka BP. Climatic conditions in the study area became relatively dry and stable after the event for about 800 years. Highly variable temperatures and humidity prevailed during the last 2000 years when an extended warm and relatively humid period occurred between 640 and 155 cal. yrs BP (AD 1310–1795) followed by predominantly colder and drier conditions. The established δ13C peat record represents the first continuous proxy for the temperature in the southern Peruvian Andes dated by the AMS 14C. Distichia peat is wide spread in the Andes and the proposed approach can be applied elsewhere in high altitudes, where no other traditional climate proxies are available.

Relationships between altitudinal gradient and plant carbon isotope composition of grassland communities on the Qinghai-Tibet Plateau, China

Foliar and root carbon isotope composition (δ13C) of grassland communities on the Qinghai-Tibet Plateau, China, was obtained by the biomass weighting method and direct measurement. We investigated the characteristics and altitudinal patterns of foliar and root δ13C and determined which environmental factors influenced foliar δ13C most. Foliar δ13C of alpine steppe was significantly higher than that of alpine meadow and temperate steppe. For alpine meadow, root δ13C was significantly higher than of foliar δ13C. Foliar δ13C increased with altitude at an average rate of 0.60‰ km−1 for the whole grassland ecosystem. This rate was lower than that at species level. However, there were no significant relationships between root δ13C and altitude. Atmospheric pressure was a more important factor than temperature and precipitation in its influence on the altitudinal pattern of foliar δ13C at the community level.

Carbon stable isotope analysis of cereal remains as a way to reconstruct water availability: preliminary results

Reconstructing past water availability, both as rainfall and irrigation, is important to answer questions about the way society reacts to climate and its changes and the role of irrigation in the development of social complexity. Carbon stable isotope analysis of archaeobotanical remains is a potentially valuable method for reconstructing water availability. To further define the relationship between water availability and plant carbon isotope composition and to set up baseline values for the Southern Levant, grains of experimentally grown barley and sorghum were studied. The cereal crops were grown at three stations under five different irrigation regimes in Jordan. Results indicate that a positive but weak relationship exists between irrigation regime and total water input of barley grains, but no relationship was found for sorghum. The relationship for barley is site-specific and inter-annual variation was present at Deir ‘Alla, but not at Ramtha and Khirbet as-Samra.

Clarifying the influence of water availability and plant types on carbon isotope discrimination by C3 plants

We are pleased that the results of Kohn (1) so strongly support our findings published earlier in PNAS (2). Both studies (1, 2) analyzed published measurements of the carbon isotope composition of plants and quantified relationships between isotopic fractionation and environmental factors at large spatial scales. These relationships will be useful when interpreting archives of plant-derived carbon, such as fossils, soil organic matter, and plant biomarkers. Kohn (1) emphasized differences between the two papers, particularly the coefficients and proportion of variance explained in regression models, but the major findings were the same: water availability [estimated by mean annual precipitation (MAP)] explains most of the observed variability in δ13C values …

Effect of Varying Crop Load on Leaf Photosynthesis and Carbon Isotope Discrimination of `Imperial Gala' Apple Tree

Crop load (CL) is a critical regulator of production and quality on apple. It affects leaf photosynthetic rate and usually an increase is detected in leaves close to developing sinks. The objective of this work was to test if 13C discrimination during photosynthesis could be an indicator of carbon sink limitation. The natural plant carbon isotope composition (13C/12C ratio: d13C) is an indicator of water use efficiency and it is an effective tool to study environmental stresses in plants. Seven-year-old trees of Imperial Gala/Bud 9 (n=30), field-grown at the Clarksville Horticultural Research Station in Michigan, were hand-thinned to five levels of CL manipulating the leaf to fruit ratio (LFR: 4, 8, 16, 32, 64) after June drop. Net photosynthetic rate (A) of leaves was monitored daily during the season and elevated rates were observed in low LFR. The A was inhibited in low CL trees (LFR 32 and 64) more in the afternoon (from 20% to 42% in relation to normal CL: LFR 16) than in the morning (from 5% to 20%), and stomatal conductance declined over the afternoon. Shoot and fruit growth were affected (fruit size –11/+11%, shoot length –13/+18% from normal CL; LFR 16). Variations of the stable carbon isotope composition of leaves show a significant reduction of 13C discrimination in low CL trees (–3.2%: d13C –25.82) and an increase of 13C discrimination (+2.7%: d13C –27.38) in relation to normal CL trees (LFR 15.63). The results were similar to those reported in 2004, which imply isotopic discrimination in relation to source limitation. This is the opposite of what you would expect under water stress conditions. Although trees were well-watered during the season, the effect of water stress on apple trees and its interaction with source limitation will be discussed.

Carbon isotope composition as a tool to control the quality of herbs and medicinal plants

Isotope screening is a simple test for determining the photosynthetic pathway used by plants. The scope of this work was to classify the photosynthetic type of some herbs and medicinal plants through studies of the carbon isotope composition (δ13C). Also, we propose the use of carbon isotope composition as a tool to control the quality of herbs and medicinal plants. For studies of δ13C, δ13C‰ = [R (sample)/R (standard) - 1] × 10-3, dry leaves powdered in cryogenic mill were analyzed in a mass spectrometer coupled with an elemental analyzer for determining the ratio R = 13CO2/12CO2. In investigation of δ13C of 55 species, 23 botanical families, and 44 species possessed a C3 photosynthetic type. Six species found among the botanical families Euphorbiaceae and Poaceae were C4 plants, and 5 species found among the botanical families Agavaceae, Euphorbiaceae, and Liliaceae possessed CAM-type photosynthesis. Carbon isotope composition of plants can be used as quality control of herbs and medicinal plants, allowing the identification of frauds or contaminations. Also, the information about the photosynthetic type found for these plants can help in introducing and cultivating exotic and wild herbs and medicinal plants.

Leaf carbon isotope composition of fossil and extant oaks grown under differing atmospheric CO2 levels

The aim of this study is to investigate the effects of long-term variations in atmospheric CO 2 levels ( p CO 2 ) on stable carbon isotope ratios in plants. Isotope measurements were undertaken on two kinds of oak leaves: fossil leaves originating from two Miocene levels of well-documented and differing p CO 2 (i.e., 280 and 360 ppmv), and extant leaves of the same species coming from plants experimentally grown under contrasted p CO 2 . Measurements were performed separately on sun and shade leaves to avoid bias linked to leaf morphotype, and on bulk leaves and individual n -alkanes extracted from the leaves, to detect possible diagenetic alteration of the isotope signal. Although extant oaks exhibit no significant trend in isotope discrimination with varying p CO 2 , fossil oaks from the high p CO 2 level tend to exhibit slightly smaller isotope discrimination than those from the low p CO 2 level. However, the difference in fossil discrimination is only of 0.5‰ and its origin cannot be unequivocally assessed since other environmental parameters could be responsible for it. Therefore, it appears that if plant carbon isotope composition is sensitive to long-term p CO 2 variations, its response is rather minimal.

Leaf carbon isotope composition of fossil and extant oaks grown under differing atmospheric CO 2 levels

The aim of this study is to investigate the effects of long-term variations in atmospheric CO 2 levels ( pCO 2) on stable carbon isotope ratios in plants. Isotope measurements were undertaken on two kinds of oak leaves: fossil leaves originating from two Miocene levels of well-documented and differing pCO 2 (i.e., 280 and 360 ppmv), and extant leaves of the same species coming from plants experimentally grown under contrasted pCO 2. Measurements were performed separately on sun and shade leaves to avoid bias linked to leaf morphotype, and on bulk leaves and individual n-alkanes extracted from the leaves, to detect possible diagenetic alteration of the isotope signal. Although extant oaks exhibit no significant trend in isotope discrimination with varying pCO 2, fossil oaks from the high pCO 2 level tend to exhibit slightly smaller isotope discrimination than those from the low pCO 2 level. However, the difference in fossil discrimination is only of 0.5‰ and its origin cannot be unequivocally assessed since other environmental parameters could be responsible for it. Therefore, it appears that if plant carbon isotope composition is sensitive to long-term pCO 2 variations, its response is rather minimal.

The stable carbon isotope composition of the terrestrial biosphere: Modeling at scales from the leaf to the globe

Global data sets of the stable carbon isotope composition of plant leaves, of CO2 in canopy air, and of CO2 in the background atmosphere were compiled and compared to results of a global vegetation model (BIOME4) that simulated, at these three scales, the magnitude, direction, and timing of fluxes of CO2 and 13C between the biosphere and the atmosphere. Carbon isotope data on leaves were classified into 12 Plant Functional Types (PFTs), and measurements from canopy flasks were assigned to 16 biomes, for direct comparison to model results. BIOME4 simulated the observed leaf δ13C values to within 1 standard deviation of the measured mean for most PFTs. Modeled δ13C for C3 grasses, tundra shrubs, and herbaceous plants of cold climates deviated only slightly more from measurements, perhaps as a result of the wide geographic range and a limited set of measurements of these PFTs. Modeled ecosystem isotopic discrimination against 13C (Δe) averaged 18.6 globally when simulating potential natural vegetation and 18.1 when an agricultural crop mask was superimposed. The difference was mainly due to the influence of C4 agriculture in areas that are naturally dominated by C3 vegetation. Model results show a gradient in Δe among C3‐dominated biomes as a result of stomatal responses to aridity; this model result is supported by canopy air measurements. At the troposphere scale, BIOME4 was coupled to a matrix representation of an atmospheric tracer transport model to simulate seasonally varying concentrations of CO2 and 13C at remote Northern Hemisphere measuring stations. Ocean CO2 and 13C flux fields were included, using the HAMOCC3 ocean biogeochemistry model [Six and Maier‐Reimer, 1996]. Model results and observations show similar seasonal cycles, and the model reproduces the inferred latitudinal trend toward smaller isotopic discrimination by the biosphere at lower latitudes. These results indicate that biologically mediated variations in 13C discrimination by terrestrial ecosystems may be significant for atmospheric inverse modeling of carbon sources and sinks, and that such variations can be simulated using a process‐based model.

Characterization of Olive Oil by Carbon Isotope Analysis of Individual Fatty Acids: Implications for Authentication and Palaeoclimatological Changes in the Mediterranean Basin

The olive tree is the oldest (600 B.C.) cultivated tree in the soils around the Mediterrranean basin. Olive oils are available in different qualities in the EU countries. In this communication we present the chemical and isotopic composition of the fatty acids of olive oils of distinct quality grade from the most important European Union (EU) producer countries. The analytical approach utilized combined capillary column gas chromatography mass spectrometry (GC/MS) and the novel technique of compound specific isotope analysis (CSIA) through gas chromatography coupled to a stable isotope ratio mass spectrometer (IRMS) via a combustion (C) interface (GC/C/IRMS). This approach provides further insights into the control of the purity and geographical origin of oils sold as cold pressed extra virgin olive oil with certified origin appellation. The results indicate that substantial enrichment in heavy carbon isotope (13C) of the bulk oil and of individual fatty acids are related to (1) a thermally induced degradation due to deodorization or steam washing of the olive oils and (2) the potential blend with refined olive oil or other vegetable oils. The interpretation of the data is based on principal component analysis of the fatty acids concentrations and isotopic data (~13Coil, ~13C16:0 , 813C18:1) and on the ~13C16:0 vs 813C18:1 covariations. The differences in the 813C values of palmitic and oleic acids are discussed in term of biosynthesis of these acids in the plant tissue and admixture of distinct oils. The results demonstrate the importance of elucidating the metabolism and biosynthesis (chain elongation and unsaturation) of the fatty acids which cause the 13C/12C discriminations observed in the individual lipids of the vegetable oils, in order to better utilize the 613C values as indicators of adulteration and environmental changes. The effects of environment or physical factors on the carbon isotope composition of plant and trees have revealed long-term trends in the global environment changes, including the increased atmospheric CO2 excess (e.g. Freyer and Belay, 1983; Walcrof t et al., 1997). The Mediterranean region is highly affected by population increases, industrial expansion, and anthropogenic or accidental biomass burning (e.g. forest fires at Sothern France and Spain). The subject of a current project is to trace the palaeoclimatic changes in this region by using carbon isotope composition of the major fatty acids in genuine olive oil. This will enable reconstruction of climate variabilities in the late Holocene in Central Europe.

Effect of two forest grasses differing in their growth dynamics on the water relations and the growth of Quercus petraea seedlings

Interference between 1-year-old sessile oak (Quercus petraea (Mattus.) Liebl.) seedlings and two grass species (Agrostis stolonifera L. and Deschampsia cespitosa (L.) Beauv.) was evaluated during 3 years after seedling transplantation. The seedlings were grown in large containers under crossed levels of watering regimes (regular irrigation that maintained the soil at field capacity or seasonal water stress) and grass competition (with Agrostis, Deschampsia, or bare soil). After 3 years, seedling basal diameter was 2.5 times greater in the absence of competing vegetation than with one of the two grasses. Within the grass-competition treatments, diameter was 1.3 times as great for the seedlings grown in the irrigated treatments than for the seedlings grown in the water-stressed treatments and was 1.3 times greater for the seedlings grown with Agrostis than for the seedlings grown with Deschampsia. During the first 2 years, the seedlings grew much faster in the bare soil than in the weedy treatments, whatever the watering level. During the 3rd year, the seedlings in all the irrigated treatments showed similar relative growth rate values, which were much higher than those in the water-stressed treatments. Each year, soil water potential reached −2.5 MPa under the two grasses and −0.7 MPa under bare soil by the end of summer. On the contrary, competition for nutrients seemed to be low. Assessments of plant carbon isotope composition showed that the seedlings in the weedy water-stressed treatments had higher intrinsic water-use efficiency, and also suggested that the competition exerted by the two grasses occurred mainly for water. We conclude that during the first 2 years, the negative effects of the two grass species on seedling growth seemed to be largely independent of any competition for water. Conversely, during the 3rd year, the influence of the grasses on the seedlings seemed to be related only to competition for water. Keywords: root interactions, water stress, osmotic adjustment, carbon isotope discrimination, classical growth analysis.

Effect of competition on stable carbon isotope ratios of two tussock grass species.

Previous studies have shown that plant carbon isotope composition varies when plants experience differences in water and nutrient availability. However, none have addressed the effect of root interactions, including competition for these soil resources, on carbon isotope ratios. We studied the effect of interspecific root interactions on the productivity and carbon isotope ratios of two Great Basin tussock grass species (Agropyron desertorum and Pseudoroegneria spicata). We compared grasses grown in mixture with sagebrush (Artemisia tridentara) to grasses in similar mixtures but where root interactions with sagebrush were limited by fiberglass partitions. During both years of the study, tussocks growing in competition with sagebrush produced tissue with more negative δ13C values than grasses experiencing limited root interaction with sagebrush. The magnitude of this difference (0.5 to 0.9%) is similar to that found in other studies when soil fertility and moisture availability were altered.

Water use efficiency and carbon isotope composition of plants in a cold desert environment

The effects of the availabilities of water and nitrogen on water use efficiency (WUE) of plants were investigated in a sagebrush steppe. The four species studied wereArtemisia tridentata (shrub),Ceratoides lanata (suffrutescent shrub),Elymus lanceolatus (rhizomatous grass), andElymus elymoides (tussock grass). Water and nitrogen levels were manipulated in a two-by-two factorial design resulting in four treatments: control (no additions), added water, added nitrogen, and added water and nitrogen. One instantaneous and two long-term indicators of WUE were used to testa priori predictions of the ranking of WUE among treatments. The short-term indicator was the instantaneous ratio of assimilation to transpiration (A/E). The long-term measures were 1) the slope of the relationship between conductance to water vapor and maximum assimilation and 2) the carbon isotope composition (δ(13)C) of plant material. Additional water decreased WUE, whereas additional nitrogen increased WUE. For both A/E and δ(13)C, the mean for added nitrogen alone was significantly greater than the mean for added water alone, and means for the control and added water and nitrogen fell in between. This ranking of WUE supported the hypothesis that both water and nitrogen limit plant gas exchange in this semiarid environment. The short- and long-term indicators were in agreement, providing evidence in support of theoretical models concerning the water cost of carbon assimilation.

δ13C signature of organic carbon in estuarine bottom sediment as an indicator of carbon export from adjacent marshes

The δ13C signature of organic carbon in estuarine bottom sediment in Louisiana Barataria Basin was used for estimating carbon flux from adjacent marsh. The stable carbon isotope composition of plants, soils and sediments from the basin were determined. The δ13C content of marsh vegetation ranged from -26.3 to -27.8% for C3 freshwater vegetation in the upper basin to -13.0 to -13.3% for C4 vegetation in the lower basin. The δ13C content of the highly organic marsh soils were similar to δ13C content of vegetation present. The δ13C content of organic carbon from bottom sediment of open water bodies ranged from 27.3 in the upper basin (freshwater) to 16.4 in bottom sediment of salt marsh ponds. The13C signature of organic carbon in bottom sediment from saline regions corresponded to the size of the body of water. The smaller salt marsh ponds contain sediment with δ13C values close to that of the C4 plantSpartina alterniflora. Results suggest that phytoplankton rather thanSpartina alterniffora is the likely organic source in bottom sediment of the larger bay near the coast (e.g. Caminada Bay).

Insect food preferences analysed using 13C/12C ratios.

Stable carbon isotope ratio analysis is a powerful technique in tracing ecosystem carbon flows, especially those between primary and secondary producers. The distinctive 13C/12C ratios of plant species tend to pass along the food chain with little further fractionation, hence the stable carbon isotope composition of an animal is an important clue to what it has eaten. We compared the stable carbon isotope composition of plants and insects in an old field in Georgia. Of the dominant plants in the old field, 6 were C4 species and had δ13C1 values of-10.9‰ to 12.9‰, and 7 were C3 species with values of-27.3‰ to-29.1‰. Insects known to be feeding on only one plant species had δ13C values within 1‰ of the isotopic composition of the plant. Wasp larvae parasitizing two insect species had δ13C values 1.3 and 1.7‰ higher than that of the food plant. A variety of insects of unknown food habits collected on monospecific and mixed species plant stands in the old field had δ13C values ranging from-10.1‰ to-30.0‰. Two species of leafhopper and a grasshopper had isotopic compositions within the range of C4 plant values; a tortoise beetle and a lace bug had isotopic compositions within C3 plant values. Other insects had intermediate δ13C values, suggesting a mixed diet composed of both C3 and C4 plants. The carbon isotopic ratios of field collected insects appears to be a useful qualitative indicator of their feeding preference.