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The key components of crassulacean acid metabolism (CAM) – nocturnal fixation of atmospheric CO2 and its processing via Rubisco in the subsequent light period – are now reasonably well understood in terms of the biochemical reactions defining this water-saving mode of carbon assimilation. Phenotypically, however, the degree to which plants engage in the CAM cycle relative to regular C3 photosynthesis is highly variable. Depending upon species, ontogeny and environment, the contribution of nocturnal CO2 fixation to 24-h carbon gain can range continuously from close to 0% to 100%. Nevertheless, not all possible combinations of light and dark CO2 fixation appear equally common. Large-scale surveys of carbon-isotope ratios typically show a strongly bimodal frequency distribution, with relatively few intermediate values. Recent research has revealed that many species capable of low-level CAM activity are nested within the peak of C3-type isotope signatures. While questions remain concerning the adaptive significance of dark CO2 fixation in such species, plants with low-level CAM should prove valuable models for investigating the discrete changes in genetic architecture and gene expression that have enabled the evolutionary transition from C3 to CAM.

Analysing functional traits along environmental gradients can improve our understanding of the mechanisms structuring plant communities. Within forests, vertical gradients in light intensity, temperature and humidity are often pronounced. Vascular epiphytes are particularly suitable for studying the influence of these vertical gradients on functional traits because they lack contact with the soil and thus individual plants are entirely exposed to different environmental conditions, from the dark and humid understorey to the sunny and dry outer canopy. In this study, we analysed multiple aspects of the trait‐based ecology of vascular epiphytes: shifts in trait values with height above ground (as a proxy for vertical environmental gradients) at community and species level, the importance of intra‐ vs. interspecific trait variability, and trait differences among taxonomic groups. We assessed ten leaf traits for 1151 individuals belonging to 83 epiphyte species of all major taxonomic groups co‐occurring in a Panamanian lowland forest. Community mean trait values of many leaf traits were strongly correlated with height and particularly specific leaf area and chlorophyll concentration showed nonlinear, negative trends. Intraspecific trait variability was pronounced and accounted for one‐third of total observed trait variance. Intraspecific trait adjustments along the vertical gradient were common and seventy per cent of all species showed significant trait–height relationships. In addition, intraspecific trait variability was positively correlated with the vertical range occupied by species. We observed significant trait differences between major taxonomic groups (orchids, ferns, aroids, bromeliads). In ferns, for instance, leaf dry matter content was almost twofold higher than in the other taxonomic groups. This indicates that some leaf traits are taxonomically conserved. Our study demonstrates that vertical environmental gradients strongly influence functional traits of vascular epiphytes. In order to understand community composition along such gradients, it is central to study several aspects of trait‐based ecology, including both community and intraspecific trends of multiple traits.

Estimates suggest billions of dollars are lost annually in the US due to fuel tax fraud. One method of fuel fraud is called “cocktailing” and involves blending products that are non-taxed, lower value, taxed at a lower rate, or unwanted/less-refined petroleum to diesel fuels. The goal of this study was to investigate compound specific isotope analysis (CSIA) using isotope ratio mass spectrometry (IRMS) for small aromatics contained in diesel fuel to determine whether this approach could be used to identify cocktailing and potentially fingerprint possible sources. However, the high chemical complexity of diesel fuels complicates CSIA owing to the need to fully separate individual compounds for effective isotope analysis. Therefore, different methods were investigated to selectively isolate aromatics for CSIA and evaluate these methods for isotopic fractionation. Analyses indicate that there is enough variability in isotopic ratios (δ2H and δ13C) between toluene samples obtained from different sources to use CSIA to differentiate/identify the origin of potential fuel adulterants. Three isolation methods were identified that provided sufficiently pure aromatic fractions for CSIA: selective solvent extraction, ionic liquid coated solid phase microextraction (SPME), and a combination of the two. However, due to the labor-intensive nature of selective solvent extraction, ionic liquid coated SPME represents the best method to quickly isolate aromatics from diesel fuel, without sacrificing selectivity or sensitivity. All methods tested can result in isotopic fractionation, but this can be compensated for by applying a correction factor. Furthermore, the chemical composition of a sample appeared to be important in the degree to which fractionation occurred during isolation. While the tested approaches for aromatic extraction from diesel showed promise, additional studies are required to refine and validate the methods prior to routine use in fuel cocktailing investigations. [Display omitted] •Toluene from diverse sources has adequate δ2H and δ13C variability for isotopic differentiation from other chemicals in a fuel.•Four different isolation methods coupled with CSIA of small aromatics in diesel fuel were evaluated.•Three isolation methods provided sufficiently pure aromatic fractions for CSIA, ionic liquid coated SPME was the best.•All isolation methods resulted in some isotopic fractionation; however, this is amenable to mathematical correction

• Leaf area (LA), mass per area (LMA), nitrogen per unit area (Narea) and the leaf-internal to ambient CO₂ ratio (χ) are fundamental traits for plant functional ecology and vegetation modelling. Here we aimed to assess how their variation, within and between species, tracks environmental gradients. • Measurements were made on 705 species from 116 sites within a broad north–south transect from tropical to temperate Australia. Trait responses to environment were quantified using multiple regression; within- and between-species responses were compared using analysis of covariance and trait-gradient analysis. • Leaf area, the leaf economics spectrum (indexed by LMA and Narea) and χ (from stable carbon isotope ratios) varied almost independently among species. Across sites, however, χ and LA increased with mean growing-season temperature (mGDD₀) and decreased with vapour pressure deficit (mVPD₀) and soil pH. LMA and Narea showed the reverse pattern. Climate responses agreed with expectations based on optimality principles. Within-species variability contributed < 10% to geographical variation in LA but > 90% for χ, with LMA and Narea intermediate. • These findings support the hypothesis that acclimation within individuals, adaptation within species and selection among species combine to create predictable relationships between traits and environment. However, the contribution of acclimation/adaptation vs species selection differs among traits.

This research was supported by the Spanish Government projects CGL2013-48074-P, AGL 2012-40039-C02 and AGL 2012- 40151-C03, the Catalan Government project SGR 2014-274 and the European Research Council Synergy grant ERC-2013- SyG-610028 IMBALANCE-P. The Spanish Government funded the FPU predoctoral fellowship to P.M-G., the FPI predoctoral fellowship and travel grant to A.B., and the Ram on y Cajal Programme to J.P.F. (RYC-2008-02050) and S.P. (RYC- 2013-14164).

The oldest minerals on Earth are thought to have formed in the Hadean eon, but the reliability of the dates has been questioned. Atom-probe tomography of an ancient zircon confirms that the mineral formed about 4.4 billion years ago, implying that any mixing event of the silicate Earth occurred before that time. The only physical evidence from the earliest phases of Earth’s evolution comes from zircons, ancient mineral grains that can be dated using the U–Th–Pb geochronometer 1 . Oxygen isotope ratios from such zircons have been used to infer when the hydrosphere and conditions habitable to life were established 2 , 3 . Chemical homogenization of Earth’s crust and the existence of a magma ocean have not been dated directly, but must have occurred earlier 4 . However, the accuracy of the U–Pb zircon ages can plausibly be biased by poorly understood processes of intracrystalline Pb mobility 5 , 6 , 7 . Here we use atom-probe tomography 8 to identify and map individual atoms in the oldest concordant grain from Earth, a 4.4-Gyr-old Hadean zircon with a high-temperature overgrowth that formed about 1 Gyr after the mineral’s core. Isolated nanoclusters, measuring about 10 nm and spaced 10–50 nm apart, are enriched in incompatible elements including radiogenic Pb with unusually high 207 Pb/ 206 Pb ratios. We demonstrate that the length scales of these clusters make U–Pb age biasing impossible, and that they formed during the later reheating event. Our tomography data thereby confirm that any mixing event of the silicate Earth must have occurred before 4.4 Gyr ago, consistent with magma ocean formation by an early moon-forming impact 4 about 4.5 Gyr ago.

For approximately the first 2 billion years of the Earth’s history, atmospheric oxygen levels were extremely low. It was not until at least half a billion years after the evolution of oxygenic photosynthesis, perhaps as early as 3 billion years ago, that oxygen rose to appreciable levels during the Great Oxidation Event. Shortly after, marine carbonates underwent a large positive spike in carbon isotope ratios known as the Lomagundi event. The mechanisms responsible for the Great Oxidation and Lomagundi events remain debated. Using a carbon–oxygen box model that tracks the Earth’s surface and interior carbon fluxes and reservoirs, while also tracking carbon isotopes and atmospheric oxygen levels, we demonstrate that about 2.5 billion years ago a tectonic transition that resulted in increased volcanic CO2 emissions could have led to increased deposition of both carbonates and organic carbon (organic C) via enhanced weathering and nutrient delivery to oceans. Increased burial of carbonates and organic C would have allowed the accumulation of atmospheric oxygen while also increasing the delivery of carbon to subduction zones. Coupled with preferential release of carbonates at arc volcanoes and deep recycling of organic C to ocean island volcanoes, we find that such a tectonic transition can simultaneously explain the Great Oxidation and Lomagundi events without any change in the fraction of carbon buried as organic C relative to carbonate, which is often invoked to explain carbon isotope excursions.

Purpose Over-accumulation of cadmium and lead in rice grain is a global concern as it has adverse health impacts. Atmospheric deposition is an important source of heavy metal accumulation in soil, but contribution to crops has not been quantified and the mechanisms of foliar Cd and Pb uptake via the stomata of rice leaves exposed to atmospheric fallout are unclear. Methods To quantify the contribution of atmospheric deposition on Cd and Pb accumulation in rice grains, a rice pot experiment with four exposure treatments (T1, all day exposure without geotextile membranes; T2, all day exposure with geotextile membranes; T3, daytime exposure with geotextile membranes; and T4, night exposure with geotextile membranes) using severely (ZZ) and moderately (XT) polluted soils was conducted. Results Cd content in shoots and roots was T1 > T2, T3 > T4 in XT soils, and T1 > T2, T4 > T3 in ZZ soils, while Pb content in both soils was T1 > T2, and T4 > T3. Cd and Pb contents in rice grains showed the same trend. Using the isotope ratios tracing method ( 114/111 Cd, 112/111 Cd, and 207/206 Pb, 208/206 Pb), it can be concluded that the contribution of atmospheric deposition to rice grains was quantified as 63.55% and 18.01% for Cd, and 27.69% and 41.13% for Pb in XT and ZZ soils, respectively. Conclusions Foliar uptake atmospheric deposition had substantial effect on Cd and Pb accumulation in rice grains and the control of heavy metal foliar uptake should be paid more attention to maintain rice safety production. Graphical abstract

Vanillin, one of the world’s most popular flavor used in food and pharmaceutical industries, is extracted from vanilla beans or obtained (bio)-synthetically. The price of natural vanillin is considerably higher than that of its synthetic alternative which leads increasingly to counterfeit vanillin. Here, we describe the workflow of combining carbon isotope ratio combustion mass spectrometry with quantitative carbon nuclear magnetic resonance spectrometry (13C-qNMR) to obtain carbon isotope measurements traceable to the Vienna Peedee Belemnite (VPDB) with 0.7‰ combined standard uncertainty (or expanded uncertainty of 1.4‰ at 95% confidence level). We perform these measurements on qualified Bruker 400 MHz instruments to certify site-specific carbon isotope delta values in two vanillin materials, VANA-1 and VANB-1, believed to be the first intramolecular isotopic certified reference material (CRMs).

Oxygen isotope ratios (δ18O) of tree-ring cellulose are a novel proxy for summer hydroclimate in monsoonal Asia. In central Japan, we collected 67 conifer wood samples, mainly Chamaecyparis obtusa, with ages encompassing the past 2600 years. The samples were taken from living trees, archeological wood, architectural wood, and buried logs. We analyzed stable isotope ratios of oxygen (δ18O) and hydrogen (δ2H) in tree-ring cellulose in these samples (more than 15 000 rings in total) without using a pooling method and constructed a statistically reliable tree-ring cellulose δ18O time series for the past 2500 years. However, there were distinct age trends and level offsets in the δ18O record, and cellulose δ18O values showed a gradual decrease as an individual tree matures. This suggested it is difficult to establish a cellulose δ18O chronology for low-frequency signals by simple averaging of all the δ18O time series data. In addition, there were opposite age trends in the cellulose δ2H, and δ2H gradually increased with tree age. There were clear positive correlations in the short-periodicity variations between δ18O and δ2H, probably indicating a common climate signal. A comparison of the δ18O and δ2H time series in individual trees with tree-ring width suggested that the opposite age trends of δ18O and δ2H are caused by temporal changes in the degree of post-photosynthetic isotope exchange with xylem water (physiological effect), accompanied by changes in stem growth rate that are influenced by human activity in the forests of central Japan. Based on the assumptions that cellulose δ18O and δ2H vary positively and negatively with constant proportional coefficients due to climatological and physiological effects, respectively, we solved simultaneous equations for the climatological and physiological components of variations in tree-ring cellulose δ18O and δ2H in order to remove the age trend. This enabled us to evaluate the climatic record from cellulose δ18O variations. The extracted climatological component in the cellulose δ18O for the past 2600 years in central Japan was well correlated with numerous instrumental, historical, and paleoclimatological records of past summer climate at various spatial and temporal scales. This indicates that integration of tree-ring cellulose δ18O and δ2H data is a promising method to reconstruct past summer climate variations on annual to millennial timescales, irrespective of the growth environment. However, analytical and statistical methods need to be improved for further development of this climate proxy.