Search

The stable carbon isotopic composition (δ13C) of fossil leaves is a simple and common measurement that provides information about paleophysiology, paleoecology, and paleoclimate. Variance in δ13C is typically assessed across leaves; comparatively little is known about variance within leaves, a potential source of unquantified uncertainty. Here we systematically analyze the spatial patterns of bulk δ13C in fresh leaves of 10 tree species (two leaves per species; 21 or 22 analyses per leaf). We find that samples containing midvein tissue are markedly higher in δ13C than non-midvein tissue from the same leaf (median = +0.85‰), with samples containing only midvein tissue offset by as much as +3.01‰. The non-midvein samples are less variable—the typical range within a single leaf is

Long-term carbon cycle models are critical for understanding the levels and underlying controls of atmospheric CO2 over geological time-scales. We have refined the implementation of two important boundary conditions in carbon cycle models, namely consumption by silicate weathering and carbon degassing. Through the construction of continental flooding maps for the past 520 million years (Myrs), we have estimated exposed land area relative to the present-day (fA), and the fraction of exposed land area undergoing silicate weathering (fAW-fA). The latter is based on the amount of exposed land within the tropics (±10°) plus the northern/southern wet belts (±40-50°) relative to today, which are the prime regions for silicate weathering. We also evaluated climate gradients and potential weatherability by examining the distribution of climate-sensitive indicators. This is particularly important during and after Pangea formation, when we reduce fAW-fA during times when arid equatorial regions were present. We also estimated carbon degassing for the past 410 Myrs using the subduction flux from full-plate models as a proxy. We further used the subduction flux to scale and normalize the arc-related zircon age distribution (arc-activity), allowing us to estimate carbon degassing in much deeper time. The effect of these refined modelling parameters for weathering and degassing was then tested in the GEOCARBSULFvolc model, and the results are compared to other carbon cycle models and CO2 proxies. The use of arc-activity as a proxy for carbon degassing brings Mesozoic model estimates closer to CO2 proxy values but our models are highly sensitive to the definition of fAW-fA. Considering only variations in the land availability to weathering that occur in tropical latitudes (corrected for arid regions) and the use of our new degassing estimates leads to notably higher CO2 levels in the Mesozoic, and a better fit with the CO2 proxies.

PREMISE The Eocene-Oligocene transition (EOT; 34-33 Ma) was marked by global cooling and increased seasonality and aridity, leading to a shift in North American floras from subtropical forests to deciduous hardwood forests similar to today. This shift is well documented taxonomically and biogeographically, but its ecological nature is less known. METHODS Using the relationship between petiole cross-sectional area and leaf mass, we estimated leaf dry mass per area (LMA), a functional trait tied to plant resource investment and expenditure, at 22 western North American sites spanning the EOT to determine how the broad restructuring of vegetation during this time was reflected in leaf economics. RESULTS There was no overall shift in LMA between pre-EOT and post-EOT floras; instead, changes in LMA across sites were mostly driven by a negative correlation with dry-season precipitation and a positive correlation with paleoelevation. These patterns held for both whole sites and subsets of sites containing taxa with similar biogeographical histories (taxa that persisted in the highlands across the EOT or that migrated to the lowlands) and are consistent with most observations in extant floras. CONCLUSIONS Our data provide a geological context for understanding environmentally paced changes in leaf-economic strategies, particularly linking leaf economic strategies to dry-season precipitation and paleoelevation.

Plate tectonics regulates atmospheric greenhouse gas concentrations and surface temperatures via sources (mainly volcanic CO2 degassing) and sinks (silicate weathering and carbonate deposition). To constrain arc-volcanism, the main source of CO2, we argue that normalized subduction flux calculated from full-plate models is a reliable proxy, and notable peaks are observed during greenhouse conditions (e.g. the Early Cretaceous), whereas icehouse conditions are commonly characterized by reduced subduction flux (e.g. the Late Paleozoic Ice Age). The age distributions of arc-related zircons grossly mimic subduction fluxes and we present a new approach to estimate degassing through time by rescaling the global zircon age distribution to the subduction flux. Importantly, this approach permits estimation of plate tectonic degassing in deep time when full-plate models become increasingly unreliable. Full-plate models differ vividly before the assembly of Pangea, mainly due to different longitude-calibrations of continents and synthetic (“made-up”) oceanic realms, and variations in zircon-age-frequency allow us to estimate changes in volcanic arc-activity or plate tectonic degassing much more objectively in deep time. A first attempt to quantify volcanic arc-activity in deep time shows a pattern where low (high) degassing generally corresponds to periods of icehouse (greenhouse) for the past 3.5 billion years. We recognize a major shift in volcanic arc activity during the late Neoproterozoic (700-540 Ma) and this may reflect a transition to a modern-type plate tectonic regime with cold, deep and steep subduction.

Purpose Infective endocarditis (IE) is a rare but potentially fatal complication following heart transplantation (HTx). There is a lack of literature regarding the patterns and clinical course of IE development following HTx. We sought to pool the existing data in regards to defining characteristics, management options, and outcomes of IE following HTx. Methods An electronic search of Cochrane Central Register of Controlled Trials, Cumulative Index to Nursing and Allied Health Literature, Ovid Medline, and the Scopus databases were performed to identify all articles in the English literature that report IE following HTx in adult patients. Patient-level data were extracted and analyzed. Results Systematic search yielded 57 patients from 32 articles. Median patient age was 52 [IQR 43, 59] and 75% of patients (43/57) were male. Median time to IE presentation post-HTx was 8.4 [IQR 3.0, 35.8] months. IE of the mitral valve was observed in 36.8% (21/57) of patients, followed by mural IE in 24.6% (14/57), and tricuspid valve IE in 21.1% (12/57). The most common organisms were Staphylococcus aureus in 26.3% (15/57), Aspergillus fumigatus in 19.3% (11/57), Enterococcus faecalis in 12.3% (7/57), and an undetermined or unspecified organism in 14.0% (8/57) patients. Overall case fatality was 44.6% (25/56). Fungal IE was associated with a significantly higher case fatality 75.0% (9/12) than that of bacterial IE 36.1% (13/36) (p = 0.02). Surgical management of post-HTx IE was observed in 35.1% (20/57) of patients. This included valve surgery for 70.0% (14/20), including the mitral valve in 50.0% (7/14), aortic valve in 35.7% (5/14), and the tricuspid valve in 14.3% (2/14) of patients. Conclusion In addition to bacterial organisms, fungi also represent a frequent cause of IE in post-HTx patients. Overall HTx patient survival in the setting of IE is poor and may be worse if caused by A. fumigatus.

Background and AimsLeaf size has considerable ecological relevance, making it desirable to obtain leaf size estimations for as many species worldwide as possible. Current global databases, such as TRY, contain leaf size data for ~30 000 species, which is only ~8% of known species worldwide. Yet, taxonomic descriptions exist for the large majority of the remainder. Here we propose a simple method to exploit information on leaf length, width and shape from species descriptions to robustly estimate leaf areas, thus closing this considerable knowledge gap for this important plant functional trait.MethodsUsing a global dataset of all major leaf shapes measured on 3125 leaves from 780 taxa, we quantified scaling functions that estimate leaf size as a product of leaf length, width and a leaf shape-specific correction factor. We validated our method by comparing leaf size estimates with those obtained from image recognition software and compared our approach with the widely used correction factor of 2/3.Key ResultsCorrection factors ranged from 0.39 for highly dissected, lobed leaves to 0.79 for oblate leaves. Leaf size estimation using leaf shape-specific correction factors was more accurate and precise than estimates obtained from the correction factor of 2/3.ConclusionOur method presents a tractable solution to accurately estimate leaf size when only information on leaf length, width and shape is available or when labour and time constraints prevent usage of image recognition software. We see promise in applying our method to data from species descriptions (including from fossils), databases, field work and on herbarium vouchers, especially when non-destructive in situ measurements are needed.

Coal balls are calcium carbonate accumulations that permineralized peat in paleotropical Permo-Carboniferous (∼320–250 Ma) mires. The formation of coal balls has been debated for over a century yet a widely applicable model is lacking. Two observations have been particularly challenging to explain: 1) the narrow temporal occurrence of coal balls and 2) their typical elemental (high Mg) and isotopic (low δ18O) composition that paradoxically indicate marine and freshwater origins, respectively. We evaluate a new model in which coal balls formed as CO2 escaped from the peat by diffusion through unusual air-filled spaces in the rootlets of lycopsid trees; critically, these trees were very common in paleotropical mires, and their evolutionary range matches the temporal range of coal balls. The episodic delivery of seawater and marine carbonate sediment to coastal mires is the first step in our model, although other pathways for the delivery of divalent cations are permissible. Subsequent dilution by freshwater and dissolution of these carbonates at the elevated CO2 of the mire subsurface is followed by the transport of CO2 through the rootlet airspaces and into the overlying water and atmosphere, which drives carbonate mineral precipitation in the sediment. We show that dilution by freshwater, because it minimally affects Mg/Ca ratios, can result in relatively low pore water δ18O values while allowing high-Mg calcite formation. This model thus explains the restriction of coal balls to the Permo-Carboniferous and resolves the discrepancy between elemental and isotopic compositions of coal ball carbonate minerals. Furthermore, we show with a 3D reactive transport model that CO2 could escape rapidly enough through the rootlets to fill 25 percent of the peat pore spaces with calcite before substantial burial (top decimeter of peat), explaining the exceptional preservation of coal swamp flora. Therefore, we suggest that coal balls are pedogenic in origin and that the disappearance of these pedogenically permineralized Histosols represents the first documented decrease in soil diversity on a vegetated planet. The rock record may thus provide important context for the modern loss and degradation of soils.

5-hydroxytryptophan (5-HTP) has shown therapeutic promise in a range of human CNS disorders. But native 5-HTP immediate release (IR) is poorly druggable, as rapid absorption causes rapid onset of adverse events, and rapid elimination causes fluctuating exposure. Recently, we reported that 5-HTP delivered as slow-release (SR) in mice augmented the brain pro-serotonergic effect of selective serotonin reuptake inhibitors (SSRIs), without the usual adverse events associated with 5-HTP IR. However, our previous study entailed translational limitations, in terms of route, dose, and duration. Here we modeled oral 5-HTP SR in mice by administering 5-HTP via the food. We modeled oral SSRI treatment via fluoxetine in the water, in a regimen recapitulating clinical pharmacokinetics and pharmacodynamics. 5-HTP SR produced plasma 5-HTP levels well within the range enhancing brain 5-HT function in humans. 5-HTP SR robustly increased brain 5-HT synthesis and levels. When administered with an SSRI, 5-HTP SR enhanced 5-HT-sensitive behaviors and neurotrophic mRNA expression. 5-HTP SR's pro-serotonergic effects were stronger in mice with endogenous brain 5-HT deficiency. In a comprehensive screen, 5-HTP SR was devoid of overt toxicological effects. The present preclinical data, appreciated in the context of published 5-HTP clinical data, suggest that 5-HTP SR could represent a new therapeutic approach to the plethora of CNS disorders potentially treatable with a pro-serotonergic drug. 5-HTP SR might in particular be therapeutically relevant when brain 5-HT deficiency is pathogenic and as an adjunctive augmentation therapy to SSRI therapy.

Leaf gas-exchange models show considerable promise as paleo-CO2 proxies. They are largely mechanistic in nature, provide well-constrained estimates even when CO2 is high, and can be applied to most subaerial, stomata-bearing leaves from C3 taxa, regardless of age or taxonomy. Here we place additional observational and theoretical constraints on one of these models, the Franks model. In order to gauge the model's general accuracy in a way that is appropriate for fossil studies, we estimated CO2 from 40 species of extant angiosperms, conifers, and ferns based only on measurements that can be made directly from fossils (leaf δ13C and stomatal density and size) and a limited sample size (1–3 leaves per species). The mean error rate is 28 %, which is similar to or better than the accuracy of other leading paleo-CO2 proxies. We find that leaf temperature and photorespiration do not strongly affect estimated CO2, although more work is warranted on the possible influence of O2 concentration on photorespiration. Leaves from the lowermost 1–2 m of closed-canopy forests should not be used because the local air δ13C value is lower than the global well-mixed value. Such leaves are not common in the fossil record, but can be identified by morphological and isotopic means.

Taphonomic processes may filter in a biased manner the tiny fraction of leaves preserved as fossils. A common perception is that large leaves are underrepresented; this is based both on intuition (large leaves are more likely to break apart) and some observations of extant vegetation. Characterizing leaf area correctly is critical for reconstructing climate and for studying evolutionary and biogeographic patterns. In extant dicotyledonous angiosperms, leaf area generally scales with the inverse of second-order vein density. This scaling offers the potential to test if fossil leaf fragments were derived from leaves that were larger than complete (or nearly complete) fossil leaves of the same species. Here we test vein scaling on 573 complete leaves from the latest Cretaceous Hell Creek Formation and earliest Paleocene Fort Union Formation in the Williston Basin of western North and South Dakota. We find a strong scaling similar to extant vegetation, with a somewhat shallower slope (1.67 vs. 2.04) and lower r2 (0.64 vs. 0.80). We apply these two scalings to 41 species-site pairs from the Williston Basin that are each represented by complete (n = 355) and fragmented (n = 387) leaves. With both scalings, the reconstructed leaf areas of fragments are on average 10% larger (±36% 1σ) than their complete companions. This small but noisy signal means that the underrepresentation of large leaves, as captured by our study design, is probably not critical for most fossil applications. Comparing directly the reconstructed areas of complete and fragmented leaves appears reasonable, thus expanding the usefulness of fossil leaf fragments.

The long-term temperature response to a given change in CO2 forcing, or Earth-system sensitivity (ESS), is a key parameter quantifying our understanding about the relationship between changes in Earth’s radiative forcing and the resulting long-term Earth-system response. Current ESS estimates are subject to sizable uncertainties. Long-term carbon cycle models can provide a useful avenue to constrain ESS, but previous efforts either use rather informal statistical approaches or focus on discrete paleoevents. Here, we improve on previous ESS estimates by using a Bayesian approach to fuse deep-time CO2 and temperature data over the last 420 Myrs with a long-term carbon cycle model. Our median ESS estimate of 3.4 °C (2.6-4.7 °C; 5-95% range) shows a narrower range than previous assessments. We show that weaker chemical weathering relative to the a priori model configuration via reduced weatherable land area yields better agreement with temperature records during the Cretaceous. Research into improving the understanding about these weathering mechanisms hence provides potentially powerful avenues to further constrain this fundamental Earth-system property., Earth-system sensitivity (ESS) describes the long-term temperature response for a given change in atmospheric CO2 and, as such, is a crucial parameter to assess future climate change. Here, the authors use a Bayesian model with data from the last 420 Myrs to reduce uncertainties and estimate ESS to be around 3.4 °C.

The inverse relationship between atmospheric CO

CO2 is the most important greenhouse gas in the Earth’s atmosphere and has fluctuated considerably over geological time. However, proxies for past CO2 concentrations have large uncertainties and are mostly limited to Devonian and younger times. Consequently, CO2 modelling plays a key role in reconstructing past climate fluctuations. Facing the limitations with the current CO2 models, we aim to refine two important forcings for CO2 levels over the Phanerozoic, namely carbon degassing and silicate weathering.Silicate weathering and carbonate deposition is widely recognized as a primary sink of carbon on geological timescales and is largely influenced by changes in climate, which in turn is linked to changes in paleogeography. The role of paleogeography on silicate weathering fluxes has been the focus of several studies in recent years. Their aims were mostly to constrain climatic parameters such as temperature and precipitation affecting weathering rates through time. However, constraining the availability of exposed land is crucial in assessing the theoretical amount of weathering on geological time scales. Associated with changes in climatic zones, the fluctuation of sea-level is critical for defining the amount of land exposed to weathering. The current reconstructions used inmodels tend to overestimate the amount of exposed land to weathering at periods with high sea levels. Through the construction of continental flooding maps, we constrain the effective land area undergoing silicate weathering for the past 520 million years. Our maps not only reflect sea-level fluctuations but also contain climate-sensitive indicators such as coal (since the Early Devonian) and evaporites to evaluate climate gradients and potential weatherablity through time. This is particularly important after the Pangea supercontinent formed but also for some time after its break-up.Whilst silicate weathering is an important CO2 sink, volcanic carbon degassing is a major source but one of the least constrained climate forcing parameters. There is no clear consensus on the history of degassing through geological time as there are no direct proxies for reconstructing carbon degassing, but various proxy methods have been postulated. We propose new estimates of plate tectonic degassing for the Phanerozoic using both subduction flux from full-plate models and zircon age distribution from arcs (arc-activity) as proxies.The effect of revised modelling parameters for weathering and degassing was tested in the well-known long-term models GEOCARBSULF and COPSE. They revealed the high influence of degassing on CO2 levels using those models, highlighting the need for enhanced research in this direction. The use of arc-activity as a proxy for carbon degassing leads to interesting responses in the Mesozoic and brings model estimates closer to CO2 proxy values. However, from simulations using simultaneously the revised input parameters (i.e weathering and degassing) large model-proxy discrepancies remain and notably for the Triassic and Jurassic.

Solid organ transplant (SOT) recipients are a complex, immunocompromised population in whom greater coronavirus disease 2019 (COVID-19) mortality has been reported compared with the general population.We examined a retrospective cohort of 58 SOT recipients with first-wave COVID-19, comparing patients with severe and nonsevere illness. Additionally, SOT recipients are compared with general patients with first-wave COVID-19.Organs transplanted included 38 kidneys, 8 livers, 5 hearts, and 3 pancreases. Average SOT recipient age was 57.4 years; 62% were male; 46.6% were African American 36.2% were white. Comorbidities included hypertension (86%), chronic kidney disease (86%), diabetes mellitus (50%), coronary artery disease (26%), and chronic obstructive pulmonary disease (14%). Twenty patients had severe COVID-19 (34.5%) and 38 had nonsevere disease (65.5%). Severe disease was more common in older SOT recipients with comorbidities and was associated with cough, dyspnea, pneumonia, C-reactive protein10 mg/L, and platelet count150/μL. Sex, race, body mass index, time from transplant, baseline immunosuppression, and diagnosis month did not differ among those with severe and nonsevere COVID-19. Seventy percent of SOT recipients were hospitalized vs 27.2% of general patients with COVID-19 and inpatient SOT recipients had a higher mechanical ventilation rate. Though a trend toward longer length of stay, higher intensive care unit admission, and greater inpatient mortality was observed (19.5% vs 14.8%), these differences were not significant.The severe acute respiratory syndrome coronavirus 2 has greatly impacted SOT recipients. One-third of our SOT recipients seen during the first wave had severe illness with associated standard risk factors for poor outcome. Compared with general first-wave patients, more SOT recipients were hospitalized, although inpatient COVID-19 mortality did not significantly differ.

Acute disseminated encephalomyelitis (ADEM) is an autoimmune demyelinating disease directed against the myelin sheath of the central nervous system that typically presents 1–4 weeks after an infection or vaccination, most commonly in children. We describe a case of a young female who presented with rapidly progressive mental deterioration and died secondary to ADEM following an adenovirus upper respiratory tract infection.

International audience; While radon in soil gases has been identified for decades as a potential precursor of volcanic eruptions, there has been a recent interest for monitoring radon in air on active volcanoes. We present here the first network of outdoor air radon sensors that was installed successfully on Mt. Etna volcano, Sicily, Italy in September 2019. Small radon sensors designed for workers and home dosimetry were tropicalized in order to be operated continuously in harsh volcanic conditions with an autonomy of several months. Two stations have been installed on the south flank of the volcano at~3000 m of elevation. A private network has been deployed in order to transfer the measurements from the stations directly to a server located in France, using a low-power wide-area transmission technology from Internet of Things (IoT) called LoRaWAN. Data finally feed a data lake, allowing flexibility in data management and sharing. A first analysis of the radon datasets confirms previous observations, while adding temporal information never accessed before. The observed performances confirm IoT solutions are very adapted to active volcano monitoring in terms of range, autonomy, and data loss.

The connections between the Earth’s interior and its surface are manifold, and defined by processes of material transfer: from the deep Earth to lithosphere, through the crust and into the interconnected systems of the atmosphere-hydrosphere-biosphere, and back again. One of the most spectacular surface expressions of such a process, with origins extending into the deep mantle, is the emplacement of large igneous provinces (LIPs), which have led to rapid climate changes and mass extinctions, but also to moments of transformation with respect to Earth’s evolving paleogeography. But equally critical are those process which involve material fluxes going the other way—as best exemplified by subduction, a key driving force behind plate tectonics, but also a key driver for long-term climate evolution through arc volcanism and degassing of CO2.Most hotspots, kimberlites, LIPs are sourced by plumes that rise from the margins of two large low shear-wave velocity provinces in the lowermost mantle. These thermochemical provinces have likely been quasi-stable for hundreds of millions, perhaps billions of years, and plume heads rise through the mantle in about 30 Myr or less. LIPs provide a direct link between the deep Earth and the atmosphere but environmental consequences depend on both their volumes and the composition of the crustal rocks they are emplaced through. LIP activity can alter the plate tectonic setting by creating and modifying plate boundaries and hence changing the paleogeography and its long-term forcing on climate. Extensive blankets of LIP-lava on the Earth’s surface can also enhance silicate weathering and potentially lead to CO2 drawdown (cooling), but we find no clear relationship between LIPs and post-emplacement variation in atmospheric CO2 proxies on very long (>10 Myrs) time-scales. Hotspot and kimberlite volcanoes generally have relatively small climate effects compared with that of LIPs (because of volumetric and flux differences), but the eruption of large kimberlite clusters, notably in the Cretaceous, could be capable of delivering enough CO2 to the atmosphere to trigger sudden global warming events.Subduction is a key driving force behind plate tectonics but also a key driver for the long-term climate evolution through arc volcanism and degassing of CO2. Subduction fluxes derived from full-plate models provide a powerful way of estimating plate tectonic CO2 degassing (sourcing). These correlate well with zircon age frequency distributions and zircon age peaks clearly correspond to intervals of high subduction flux associated with greenhouse conditions. Lows in zircon age frequency are more variable with links to both icehouse and greenhouse conditions, and only the Permo-Carboniferous (~330-275 Ma) icehouse is clearly related to the zircon and subduction flux record. A key challenge is to develop reliable full-plate models before the Devonian in order to consider the subduction flux during the end-Ordovician Hirnantian (~445 Ma) glaciations, but we also expect refinements in subduction fluxes for Mesozoic-Cenozoic times as more advanced ocean-basin models with intra-oceanic subduction are being developed and implemented in full-plate models.

Premise of the Study: The global climate during the early Miocene was warmer than the present and preceded the even warmer middle Miocene climatic optimum. The paleo-CO2 records for this interval suggest paradoxically low concentrations (95% confidence) that CO2 during the late early Miocene exceeded 400 ppm. These results revise upwards the likely CO2 concentration at this time, more in keeping with a CO2-forced greenhouse climate. © 2018 Botanical Society of America

Dust from Saharan Africa commonly blows across the Atlantic Ocean and into the Caribbean. Most methods for measuring this dust either are expensive if collected directly from the atmosphere, or depend on very small concentrations that may be chemically altered if collected from soil. Tank bromeliads in the dwarf forest of El Yunque National Forest, Puerto Rico, have a structure of overlapping leaves used to capture rainwater and other atmospheric inputs. Therefore, it is likely that these bromeliads are collecting in their tanks Saharan dust along with local inputs. Here we analyze the elemental chemistry, including rare earth elements (REEs), of tank contents in order to match their chemical fingerprint to a provenance of the Earth's crust. We find that the tank contents differ from the local soils and bedrock and are more similar to published values of Saharan dust. Our study confirms the feasibility of using bromeliad tanks to trace Saharan dust in the Caribbean.

The largest radiation of Phanerozoic marine animal life quadrupled genus-level diversity towards the end of the Ordovician Period about 450 million years ago. A leading hypothesis for this Great Ordovician Biodiversification Event is that cooling of the Ordovician climate lowered sea surface temperatures into the thermal tolerance window of many animal groups, such as corals. A complementary role for oxygenation of subsurface environments has been inferred based on the increasing abundance of skeletal carbonate, but direct constraints on atmospheric O2 levels remain elusive. Here, we use high-resolution paired bulk carbonate and organic carbon isotope records to determine the changes in isotopic fractionation between these phases throughout the Ordovician radiation. These results can be used to reconstruct atmospheric O2 levels based on the O2-dependent fractionation of carbon isotopes by photosynthesis. We find a strong temporal link between the Great Ordovician Biodiversification Event and rising O2 concentrations, a pattern that is corroborated by O2 models that use traditional carbon–sulfur mass balance. We conclude that that oxygen levels probably played an important role in regulating early Palaeozoic biodiversity levels, even after the Cambrian Explosion. An increase in biodiversity 450 million years ago coincided with a rise in atmospheric oxygen concentrations, suggests a geochemical analysis. Oxygen availability may have thus helped spur the radiation alongside climatic cooling.

Franks et al. (2014) developed a model for estimating the concentration of atmospheric CO2 (ca) that can be applied to most stomata-bearing plant fossils. In a recent paper, McElwain et al. (2016a) proposed changes to two of the key inputs: mesophyll conductance to CO2 (gm) and CO2 assimilation rate at a known ca (A0). These proposed changes lead to increases in the model-estimates of ca. Here we show a lack of support for these proposed changes. First, the downward revision of gm is the result of a mathematical error by McElwain et al. (2016a) when describing the relationship between CO2 assimilation rate (An) and gm. Once corrected, values for gm are very similar to the values recommended by Franks et al. (2014). Second, the proposed ~ 2-fold upward revision of A0 is not supported by data from extant analogs or by hydraulic constraints from fossils. Moreover, the modelled estimates of An from Franks and Beerling (2009) are in fact most consistent with the modelled An in Franks et al. (2014) using their recommended A0 values, not those proposed by McElwain et al. (2016a). These results provide further support for the strategy of model implementation outlined in Franks et al. (2014).

The δ 13 C of fossil leaf cuticle is frequently used for paleoenvironment interpretation. A tacit assumption that is common in such studies is that the δ 13 C of the cuticle is the same as the δ 13 C of the original whole leaf. We tested this assumption by measuring the isotopic fractionation between cuticle and whole leaves (e 13 C cuticle-leaf ) in 175 phylogenetically diverse species. The average e 13 C cuticle-leaf is indistinguishable from zero (-0.04 ±1.2‰ 1σ), in keeping with the few previously published data and with studies that have tracked the evolution of leaf δ 13 C during decomposition. Across species, e 13 C cuticle-leaf spans over 9‰: this variability does not covary with growth habit (woody vs. herbaceous) or climate, but does contain a strong phylogenetic signal. In particular, more basal groups (lycopsids and some gymnosperms, basal ferns, and basal angiosperms) tend to have negative e 13 C cuticle-leaf values. This variability should be accounted for in studies that wish to estimate whole-leaf δ 13 C from cuticle δ 13 C.

International audience; We report the study of direct measurement of ionization charges in an innovative liquid xenon Compton camera of small animal imaging, named XEMIS2. It was combined with a novel 3γ medical imaging modality, showing a "TOF-like" PET performance, targeted to reduce the administered activity diametrically while preserving the image quality in oncology diagnosis. For the Compton cones reconstruction, the sequential low energy electronic recoils from Compton scattering of third γray (∼ 1 MeV) are measured directly from ionization signals under a high electric field of 2 kV/cm. The Geant4/NEST simulations studies reveal that the intrinsic energy and spatial resolutions of charges carriers measuring in liquid xenon are dominated respectively by the electron-ion recombination and the abstruse trajectory of recoil electrons. Besides, a novel ASIC front-end electronic, XTRACT, and data acquisition chain were developed, dedicated to optimizing the accuracy and efficiency of ionization signals measurement in XEMIS2. It allows a continuous read-out with ultra-low charges threshold and negligible deadtime per individual channel. The performing characteristics were calibrated in the prototype XEMIS1 under the XEMIS2 operation condition, showing a good homogeneous charge linearity response. Meanwhile, the data processing and analysis were developed, where the charge measurement has been optimized through Monte Carlo simulations. I. INTRODUCTION T HE personalized medicine as the heart of healthcare priorities of the 21 st century requires molecular imag-Manuscript