Hydrogen Isotope Ratios Research Articles

Authentication of vanillin ex glucose – A first study on the influence of the glucose-source on the δ13C and δ2H value

Vanillin is the most characteristic compound in vanilla flavour. Since vanilla pods are very expensive, vanillin is mainly produced by synthetic and sometimes biosynthetic methods. Biosynthetic vanillin is called ‘biovanillin’ and can -by law-be labelled as ‘natural’. The isotopic carbon ratio (expressed as δ 13 C) is a widely established and valuable authentication parameter for vanillin. Furthermore, currently available data about δ 2 H values indicate, that the isotopic hydrogen ratio can make a decisive contribution to the authentication of vanillin. One of the most recent developments is the bio-production of vanillin derived from glucose. However, very little is known about its isotopic composition. Here, we present the δ 13 C and δ 2 H values of glucose from corn and wheat and the vanillin that was derived from these. The isotopic composition of the glucose is clearly reflected in the resulting vanillin molecule. All ‘glucose-vanillin’ samples could be distinguished from vanillin originating from other sources when combining the δ 13 C and δ 2 H value. • Carbon and hydrogen isotopic ratio characterisation of vanillin ex glucose. • Carbon and hydrogen isotopic ratio characterisation of glucose from wheat and corn. • The isotopic composition of the glucose is reflected in the derived vanillin.

Using stable isotopes and major ions to identify recharge characteristics of the Alpine groundwater-flow dominated Triglavska Bistrica River

Triglavska Bistrica is a typical Alpine river in the north-western part of Slovenia. Its recharge area includes some of the highest peaks in the Julian Alps. The hydrogeological conditions and flow of the river depend largely on groundwater exchange between the karstified aquifer in the carbonate rocks and the intergranular aquifer in the glaciofluvial deposits. The average volume of the river flow is up to several m3/s. In this study, water samples from different locations along the river were analysed for stable isotope ratios of oxygen and hydrogen, major ions, and concentration of tritium activity. The correlation of major ions suggests that the recharge area consists of both limestone and dolomite rocks. The δ18O and δ2H values decrease downstream, implying that the average recharge elevation increases. At the downstream sampling site V-5, located approx. 300 m upstream from the confluence of the Sava Dolinka River, the calculated mean recharge altitude is estimated to be 1,996 m.

The unknown third – Hydrogen isotopes in tree-ring cellulose across Europe

This is the first Europe-wide comprehensive assessment of the climatological and physiological information recorded by hydrogen isotope ratios in tree-ring cellulose (δ2Hc) based on a unique collection of annually resolved 100-year tree-ring records of two genera (Pinus and Quercus) from 17 sites (36°N to 68°N). We observed that the high-frequency climate signals in the δ2Hc chronologies were weaker than those recorded in carbon (δ13Cc) and oxygen isotope signals (δ18Oc) but similar to the tree-ring width ones (TRW). The δ2Hc climate signal strength varied across the continent and was stronger and more consistent for Pinus than for Quercus. For both genera, years with extremely dry summer conditions caused a significant 2H-enrichment in tree-ring cellulose.The δ2Hc inter-annual variability was strongly site-specific, as a result of the imprinting of climate and hydrology, but also physiological mechanisms and tree growth. To differentiate between environmental and physiological signals in δ2Hc, we investigated its relationships with δ18Oc and TRW. We found significant negative relationships between δ2Hc and TRW (7 sites), and positive ones between δ2Hc and δ18Oc (10 sites). The strength of these relationships was nonlinearly related to temperature and precipitation. Mechanistic δ2Hc models performed well for both genera at continental scale simulating average values, but they failed on capturing year-to-year δ2Hc variations. Our results suggest that the information recorded by δ2Hc is significantly different from that of δ18Oc, and has a stronger physiological component independent from climate, possibly related to the use of carbohydrate reserves for growth. Advancements in the understanding of 2H-fractionations and their relationships with climate, physiology, and species-specific traits are needed to improve the modelling and interpretation accuracy of δ2Hc. Such advancements could lead to new insights into trees' carbon allocation mechanisms, and responses to abiotic and biotic stress conditions.

Analysis of Carbon and Hydrogen Stable Isotope Ratios of Phenolic Compounds: Method Development and Biodegradation Applications

Phenolic compounds are priority water pollutants of both natural and anthropogenic origins. Distinguishing the sources and degradation pathways of phenolic compounds in the environment is essential for sustainable water management. In this study, we have developed and validated methods based on gas chromatography–isotope ratio mass spectrometry for analysis of hydrogen and carbon isotope ratios of phenol and cresols. For carbon stable isotope analysis, solid-phase extraction was applied, whereas liquid–liquid extraction, followed by derivatization with trifluoroacetic anhydride, was used for hydrogen stable isotope analysis. The methods were verified in biodegradation experiments using p-cresol and phenol as substrates. Methyl group oxidation of p-cresol by Pseudomonas pseudoalcaligenes and Aromatoleum aromaticum resulted in the strong hydrogen (−76 ± 2 and −103 ± 2 mUr, respectively) and varying carbon isotopic fractionation (−2.1 ± 0.1 and −1.0 ± 0.1 mUr, respectively), leading to distinguishable two-dimensional plots for hydrogen versus carbon isotope ratios, indicating slightly different enzymatic reactions. For anaerobic phenol degradation by Desulfosarcina cetonica, the absence of hydrogen isotopic fractionation indicates adenosine triphosphate-dependent carboxylation as the initial step of the biodegradation pathway. The methods developed in this study are useful to detect biological degradation of phenolic compounds in highly contaminated aqueous environmental systems.

Hydrogen isotope ratios as a Larix detector in archaeological wood samples

Identifying wood species in archaeological specimens is important for the evaluation of timber structures and the conservation of historic buildings. Microscopic wood anatomy is the most commonly used technique for species identification. However, its application is problematic for the analysis of deteriorated wood. In addition, a particular challenge is the distinction of Picea from Larix due to their similar microscopic features.Recently, an analysis of stable isotopes of cellulose has shown that Larix is characterized by significantly more depleted deuterium values compared to Picea as well as other conifers from the Alpine region. To verify if this fact can be used in archaeological studies, we obtained 36 specimens, most of which were not clearly identified as larch or spruce. The cellulose could be extracted from 20 of them. We identified Larix and non-Larix species (Picea) without ambiguity from the deuterium content, except for one sample with an intermediate value. In conclusion, the evaluation of deuterium content is a valuable tool for the study of archaeologic wood.

Hydrochemical Characteristics of Groundwater at the Epicenter of the 2021 Biru M6.1 Earthquake in Central Tibet

Groundwater is undoubtedly important for water security and eco-environmental protection, especially in areas that experience earthquakes. Analyzing the characteristics and variation of groundwater after an earthquake is significant to obtain a better understanding of the seismic risk and rational management of groundwater resources. This study investigated the hydrogeochemical characteristics of groundwater at the epicenter of the 2021 Biru M6.1 earthquake in central Tibet, southwest China, using 23 water samples. The results showed that: (1) the hydrochemical type, hydrogen and oxygen isotope ratios, and SiO2 concentrations of three hot spring water samples in the study area were significantly different from those of samples taken elsewhere, indicating that the hot spring water originates from deeper geothermal reservoirs and has undergone more distant migration and longer fractionation processes; (2) the geochemical characteristics of groundwater from some sampling sites in the epicentral area were apparently distinct from those of other shallow groundwater or surface water samples, suggesting that the groundwater environment in the epicentral area has been affected by the earthquake. Along with the macroscopic groundwater responses in the epicentral area after the earthquake, we investigated the influencing mechanisms of the earthquake on the regional groundwater environment. We conclude that a shorter distance from the epicenter to the seismogenic fault leads to a greater possibility of the generation of new fractures, which then induce macroscopic responses and chemical characteristic variations for groundwater.

Characterisation of radiogenic monoalkenes in Australian oils and condensate

Thirteen Australian oils and one condensate, covering oil reservoir ages from Mesoproterozoic to Early Cretaceous, show monoalkene contents varying from 0.01 to 22.3 wt% of the whole liquid. Radiolysis of saturated hydrocarbons is the most likely process leading to oils with high alkene contents. The major radiolytic component is an unresolved complex mixture (UCM). The bulk of the resolved alkene compounds are positional isomers of n-alkenes. Methyl branched and cyclohexyl alkenes are minor components. Internal n-alkene isomers have a trans configuration dominant over the cis isomer. The oil with the longest reservoir residence time shows the highest content of internal n-alkenes relative to terminal 1-alkenes as well as the highest trans/cis ratio, suggesting the extended time has resulted in rearrangement to near thermodynamic equilibrium of the congruent monoalkenes. The radiolytic monoalkenes in the Ordovician-reservoired oil with the highest alkene content is likely influenced by a higher probability of intermolecular interactions and different product pathways in a complex mixture. Here, the relative proportion of alkene mimics the relative abundance of n-alkanes, suggesting that radiolytic C–C bond cleavage is suppressed when the alkene/alkane ratio is elevated and that the preferred pathway of n-alkane radiolysis favours the production of terminal monoalkenes. Radiolysis of the alkane UCM together with crosslinking and branching of n-alkane-derived radiolysis products contribute to the higher relative proportion of the alkene UCM. The similar carbon and hydrogen isotopic ratios of the n-alkanes and n-alkenes supports a parent–daughter relationship.

Considerations for Stable Isotope Analysis of Human Hair

Stable isotope analysis of postmortem hair is performed in order to make inferences about an individual’s diet and geographic travel history prior to death. During analysis and interpretation, investigators assume that the hair collected from a postmortem environment has not been altered by exposure conditions and that the isotopic “signatures” of hair prior to exposure are preserved in postmortem samples. In order to confidently make inferences from postmortem hair samples, it is necessary to know whether their isotope ratios undergo postmortem changes. To address this question, post-exposure hair samples (n = 44) were collected from known body donors at the Anthropology Research Facility in Knoxville, Tennessee, USA, at various time points ranging from 22 to 1,140 days of exposure. These samples were analyzed for carbon (δ13C), nitrogen (δ15N), hydrogen (δ2H), and oxygen (δ18O) isotope ratios, and the results were compared with pre-exposure hair samples collected from the same donors. This study highlights considerations for the interpretation of isotope ratios obtained from postmortem hair samples in forensic contexts. The results indicate that δ13C, δ15N, and δ18O values from human hair remain relatively consistent over periods up to three years of outdoor exposure, while δ2H values changed significantly between pre-and post-exposure hair samples.

Tracing lamb meat with stable isotope ratio analysis: a review

The analysis of stable isotopes applied to the lamb meat matrix is recognized as a technique of choice not only for geographical traceability but also for verifying the correspondence between the diet provided and the prescribed one. Indeed, a large amount of information is stored in animal tissues in terms of stable isotopes relative abundances of different elements. The purpose of this review is to critically analyze all the studies carried out on lambs, focusing in particular on the isotope ratios of carbon, nitrogen, sulfur, hydrogen and oxygen of different matrices, trying to define the different ranges of variability based on the origin and diet of the lambs. Carbon is certainly the most useful for identifying the animal diet while oxygen and hydrogen confirm their ability to geographically discriminate lambs. Overall, the results of statistical models validating isotope traceability systems can reach and exceed 90% of accuracy.

Measurement and research status of stable hydrogen isotopes in tree-ring lignin methoxyl groups

The primary hydrogen (H) source for all organic compounds in the biosphere is from water, and then participates in biogeochemical cycles through photosynthesis and plant physiological metabolism. As a new proxy of paleoclimate and paleoenvironment, stable hydrogen isotope ratios in wood lignin methoxyl groups (δ2HLM) show great advantages in the studies of paleoclimatic change and have been used to reconstruct precipitation stable hydrogen isotope ratios and paleoclimate signals in many regions. Based on the lignin application mechanism and analysis method of δ2HLM, we evaluated the stability and effectiveness of δ2HLM-measurement method from lignin content and lignin monomer composition, and expounded the tree lignin methoxyl groups' stable isotope proxies of current research outcomes. In the middle latitudes, the tree-ring δ2HLM had great potential in recording temperature signals and precipitation stable hydrogen isotope ratios. However, the study of tree-ring δ2HLM was still in its infancy as evidenced by following reasons: 1) The study area was limited to the middle latitude of the northern hemisphere, and the study subjects were limited to conifer species; 2) To compensate for the limitation of hydrogen isotopic records of nitrocellulose, high resolution tree-ring δ2HLM would be studied; 3) The potential of tree-ring δ2HLM utilization in plant physiology and forest ecology remained to be exploited.

A high-temperature water vapor equilibration method to determine non-exchangeable hydrogen isotope ratios of sugar, starch and cellulose.

The analysis of the non‐exchangeable hydrogen isotope ratio (δ2Hne) in carbohydrates is mostly limited to the structural component cellulose, while simple high‐throughput methods for δ2Hne values of non‐structural carbohydrates (NSC) such as sugar and starch do not yet exist. Here, we tested if the hot vapor equilibration method originally developed for cellulose is applicable for NSC, verified by comparison with the traditional nitration method. We set up a detailed analytical protocol and applied the method to plant extracts of leaves from species with different photosynthetic pathways (i.e., C3, C4 and CAM). δ2Hne of commercial sugars and starch from different classes and sources, ranging from −157.8 to +6.4‰, were reproducibly analysed with precision between 0.2‰ and 7.7‰. Mean δ2Hne values of sugar are lowest in C3 (−92.0‰), intermediate in C4 (−32.5‰) and highest in CAM plants (6.0‰), with NSC being 2H‐depleted compared to cellulose and sugar being generally more 2H‐enriched than starch. Our results suggest that our method can be used in future studies to disentangle 2H‐fractionation processes, for improving mechanistic δ2Hne models for leaf and tree‐ring cellulose and for further development of δ2Hne in plant carbohydrates as a potential proxy for climate, hydrology, plant metabolism and physiology.

Upwelling of Deep-seated Fluid in the Sikhote-Alin Region, Far East of the Eurasian Plate

Spring waters with high-pCO2 content are widely distributed in the Sikhote-Alin region in Russia. Mukhen spa is one such spring located in the northern Sikhote-Alin region. This spa has two types of upwelling spring waters and exhibits distinct chemical signatures. One of the springs originates from a shallow aquifer and features hydrogen and oxygen isotopic ratios of meteoric water with a high 3He/4He ratio, whereas the other originates from a deeper aquifer and features a distinctly negative δ18O with a lower 3He/4He ratio. To understand this apparent discrepancy and the water circulation dynamics beneath Mukhen springs, we utilized all published data concerning the major solute elements and isotopic ratios of Mukhen spring waters and compared them with the He isotopic compositions on several springs in the far eastern region, which are newly analyzed in this study. The results show that the shallow aquifer comprises meteoric water that interacts with the crust enhanced by the gas component welling up from deep underground, while the fluid in deep aquifer fingerprinted the hydration reaction of silicate and involves a mantle component possibly delivered by a deep-seated fluid and/or gas upwelling along the tectonic fault through the western margin of the Sikhote-Alin region.

Hydrochemical characteristics and evolution of geothermal waters in the eastern Himalayan syntaxis geothermal field, southern Tibet

The eastern Himalayan syntaxis is the easternmost end of southern Tibet and undergoing the continental Indian-Eurasian collision. The occurrence of large amounts of geothermal waters with high temperatures along the regional active faults is a clear manifestation of an abnormal thermal structure of the crust. In order to further complement the distribution characteristics of hydrothermal activity in southern Tibet, geothermal waters were collected and the hydrochemical characteristics and genetic mechanisms were analyzed. In the eastern Himalayan syntaxis geothermal field, geothermal waters show different compositional features. The major ions are Na+, Ca2+ and HCO3−, SO42−, which are mainly controlled by water-rock interaction. Two peculiar hydrochemical characteristics of geothermal waters are proposed: ⅰ) the Cl− concentration of three water samples is abnormally high due to the likely contribution of magmatic water; ⅱ) the other three have a lower Cl− concentration but higher temperature because of flashing steam heating. The positive correlations between B, Li and Cl concentrations indicate that the geothermal waters originate in a parent geothermal liquid. The enthalpy-chloride diagram shows that the Cl− concentration and the enthalpy of the parent geothermal liquid are 283 mg/L and 1732 J/g (matching a temperature of 413.74 °C), respectively. Four cooling processes for the geothermal waters which ascend from reservoirs to surface were suggested, i.e., conductive cooling, adiabatic cooling, mixing with cold groundwater and the combination of these processes. The partial melting derived from crustal anatexis or crust-mantle mixing is the heat source for this geothermal field. The oxygen and hydrogen isotopic ratios indicate that the geothermal waters are meteorically-fed. The meteoric waters infiltrate via brittle tensional small-scale faults. According to the results of hydrochemical analysis, the evolution patterns of geothermal waters have been further summarized into seven patterns. Except for Pattern g, Patterns a to f are associated with the parent geothermal liquid.

Lacustrine leaf wax hydrogen isotopes indicate strong regional climate feedbacks in Beringia since the last ice age

The Late-Quaternary climate of Beringia remains unresolved despite the region's role in modulating glacial-interglacial climate and as the likely conduit for human dispersal into the Americas. Here, we investigate Beringian temperature change using an ∼32,000-year lacustrine record of leaf wax hydrogen isotope ratios (δ2Hwax) from Arctic Alaska. Based on Monte Carlo iterations accounting for multiple sources of uncertainty, the reconstructed summertime temperatures were ∼3 °C colder (range: −8 to +3 °C) during the Last Glacial Maximum (LGM; 21-25 ka) than the pre-industrial era (PI; 2–0.1 ka). This ice-age summer cooling is substantially smaller than in other parts of the Arctic, reflecting altered atmospheric circulation and increased continentality which weakened glacial cooling in the region. Deglacial warming was punctuated by abrupt events that are largely synchronous with events seen in Greenland ice cores that originate in the North Atlantic but which are also controlled locally, such as by the opening of the Bering Strait between 13.4 and 11 ka. Our reconstruction, together with climate modeling experiments, indicates that Beringia responds more strongly to North Atlantic freshwater forcing under modern-day, open-Bering Strait conditions than under glacial conditions. Furthermore, a 2 °C increase (Monte Carlo range: −1 to +5 °C) over the anthropogenic era reverses a 6 °C decline (Monte Carlo range: −10 to 0 °C) through the Holocene, indicating that recent warming in Arctic Alaska has not surpassed peak Holocene summer warmth.

Geographical discrimination of ethanol based on stable isotope ratio analysis coupled with statistical methods: The Chinese case study

The demand for the effective traceability of hazardous chemicals is crucial for preventing and controlling chemical spills and other accidents involving hazardous chemicals. The aim of the study was to investigate the correlation between the geographical location of ethanol-producing industrial sites and the carbon, hydrogen, and oxygen stable isotope ratios of the Chinese-manufactured ethanol using statistical classification analysis to enable the traceability of the ethanol. The isotopic data of 54 ethanol samples obtained from 18 different ethanol manufacturing plants in China between 2019 and 2020. The results of the statistical analysis demonstrated that the δ18O values of the ethanol positively correlated with latitudes of the production plants but negatively correlated with the δ13C values of the ethanol. A small number of samples derived from sites that were geographically close to each other could not be visually distinguished by PCA and HCA. However, by applying and comparing the results of classification by LDA, K-NN and Ensemble, an optimal classification model was obtained. Upon application of these models, 96.3% of the ethanol samples were correctly classified based on their geographical origin, indicating that the combination of isotopic ratios and latitude data is practical and effective for measuring the traceability of ethanol.

Simultaneous determination of compound-specific isotopic compositions of acyclic isoprenoids and n-alkanes in light crude oil.

Stable carbon and hydrogen isotope ratios of individual n-alkanes and acyclic isoprenoids are important tools in petroleum geochemistry. However, the analysis requires baseline separation and peak profiles using gas chromatography-isotope ratio mass spectrometry to obtain accurate compound-specific isotope data. Time-consuming isolation or purification is typically conducted to separate the compounds to avoid co-elution with other compounds or matrices in crude oils. We developed a simple gas chromatography separation method to simultaneously measure the compound-specific carbon or hydrogen isotope compositions of n-alkanes and acyclic isoprenoids. It was achieved by direct injection of the whole crude condensate and light oil or the saturated fractions of different types of crude oils using a 60m DB-17ms column. This method simplifies the pre-treatment of compound-specific isotope analysis, saves manpower and time, and reduces the use of organic solvents to be more environmentally friendly.

Strong isotope effect in the VUV photodissociation of HOD: A possible origin of D/H isotope heterogeneity in the solar nebula.

The deuterium versus hydrogen (D/H) isotopic ratios are important to understand the source of water on Earth and other terrestrial planets. However, the determinations of D/H ratios suggest a hydrogen isotopic diversity in the planetary objects of the solar system. Photochemistry has been suggested as one source of this isotope heterogeneity. Here, we have revealed the photodissociation features of the water isotopologue (HOD) at λ = 120.8 to 121.7 nm. The results show different quantum state populations of OH and OD fragments from HOD photodissociation, suggesting strong isotope effect. The branching ratios of H + OD and D + OH channels display large isotopic fractionation, with ratios of 0.70 ± 0.10 at 121.08 nm and 0.49 ± 0.10 at 121.6 nm. Because water is abundant in the solar nebula, photodissociation of HOD should be an alternative source of the D/H isotope heterogeneity. This isotope effect must be considered in the photochemical models.

Contamination of the Bushveld Complex (South Africa) magmas by basinal brines: Stable isotopes in phlogopite from the UG2 chromitite

Abstract There is abundant evidence for significant H2O in evolved melts from the platinum-rich UG2 chromitite and the Merensky Reef of the Bushveld Complex (South Africa), but there is no consensus about the source of H2O. We report triple-oxygen and hydrogen isotope ratios of interstitial, late-magmatic phlogopite from three localities of the UG2 layer. The phlogopite yielded δD values of −43 to −23, which is >30 higher than previously known from Bushveld rocks and far above the mantle values of ~−75. The phlogopite triple-oxygen isotope ratios are the first to be reported for Bushveld rocks, with values of Δ′17O0.5305 (17O excess relative to the reference line 0.5305) from –0.069 to –0.044 (δ18O 5.2–6.2). The oxygen data support existing models of as much as 30%–40% contamination of mantle-derived magmas in the lower to middle crust. However, the high δD values require a second step of contamination, which we attribute to brines from the marine sediments in the Transvaal Basin at the emplacement level.

Late Carboniferous paleoelevation of the Variscan Belt of Western Europe

We present the first stable isotope paleoaltimetry estimates for the hinterland of the eroded Variscan Belt of Western Europe based on the hydrogen isotope ratios of muscovite from syntectonic leucogranites that have been emplaced at ∼315 Ma. We focus on the Limousin region (Western Massif Central, France) where peraluminous granites are spatially associated with strike-slip and detachment shear zones that developed as a consequence of Late Carboniferous syn- to post-orogenic extension. In this region, we show that the north-east corner of the Millevaches massif (located at the junction between brittle and ductile fault systems) represented a pathway for Earth surface-derived fluids that penetrated the crust and reached the ductile segment of the low-angle Felletin detachment zone. Using microstructural, thermometry, hydrogen isotope and 40Ar/39Ar geochronological data, we show that these Variscan meteoric fluids interacted with hydrous silicates during high temperature deformation between ∼318 and 310 Ma. For paleoaltimetry purposes, we reference our hydrogen isotope record (δD) of ancient meteoric fluids from mylonitic rocks to ∼295 Myr-old records retrieved from freshwater shark remains preserved in the Bourbon l'Archambault basin that developed in the external zones of the orogen. A ∼76‰ difference in δDmeteoric water values between the Millevaches massif (δDmeteoric water value = −96 ± 8‰) and the Bourbon l'Archambault foreland basin (δDwater value = −20 ± 6‰) is consistent with paleoaltimetry estimates of 3.4 ± 0.7 km based on a modern lapse rate of ∼-22‰/km for δDwater values. The rather large difference in δD values between the foreland basin and the continental interior suggests that the hinterland of the Variscan belt of western Europe was high enough to act as a barrier to moisture transport from the south-south-east and induce an orographic rain shadow to the north.

Metabolic exchange between pathways for isoprenoid synthesis and implications for biosynthetic hydrogen isotope fractionation.

Hydrogen isotope ratios of plant lipids are used for paleoclimate reconstruction, but are influenced by both source water and biosynthetic processes. Measuring 2 H:1 H ratios of multiple compounds produced by different pathways could allow these effects to be separated, but hydrogen isotope fractionations during isoprenoid biosynthesis remain poorly constrained. To investigate how hydrogen isotope fractionation during isoprenoid biosynthesis is influenced by molecular exchange between the cytosolic and plastidial production pathways, we paired position-specific 13 C-pyruvate labeling with hydrogen isotope measurements of lipids in Pachira aquatica saplings. We find that acetogenic compounds primarily incorporated carbon from 13 C2-pyruvate, whereas isoprenoids incorporated 13 C1- and 13 C2-pyruvate equally. This indicates that cytosolic pyruvate is primarily introduced into plastidial isoprenoids via glyceraldehyde 3-phosphate and that plastidial isoprenoid intermediates are incorporated into cytosolic isoprenoids. Probably as a result of the large differences in hydrogen isotope fractionation between plastidial and cytosolic isoprenoid pathways, sterols from P.aquatica are at least 50‰ less 2 H-enriched relative to phytol than sterols in other plants. These results provide the first experimental evidence that incorporation of plastidial intermediates reduces 2 H:1 H ratios of sterols. This suggests that relative offsets between the 2 H:1 H ratios of sterols and phytol can trace exchange between the two isoprenoid synthesis pathways.