Pourquoi s’intéresser à l’art anglais ?

Lorsque, au milieu du xviiie siècle, le premier grand peintre anglais William Hogarth commença à rencontrer un certain succès public, les « connoisseurs » de l’époque jugèrent, en forme de compliment empoisonné, que Hogarth était certes un artiste de talent mais qu’il l’était « à sa manière », in his own way. D’une certaine façon, on pourrait dire que cette appréciation eut une valeur inaugurale et prémonitoire car elle n’a, depuis, jamais cessé d’être portée, non seulement sur l’art de Hogar..

Histoire de l’art britannique 1750-1850 : un état des lieux

Grâce à une active collaboration entre universités, musées (Tate Britain, Yale Center for British Art) et centres de recherches (Warburg Institute, Paul Mellon Centre…), les recherches sur l’art britannique entre 1750 et 1850 se sont remarquablement structurées et enrichies depuis une trentaine d’années (élaboration de catalogues raisonnés, expositions thématiques, symposiums réguliers, bourses de recherche). Ces orientations nouvelles ont permis l’inscription de la production artistique britannique, en particulier à l’époque romantique, dans le contexte international (notamment italien et allemand). Non seulement des artistes jusque là laissés dans l’ombre (Stubbs, Wright of Derby, Rysbrack…), ont été étudiés, mais surtout les approches se sont élargies à l’histoire sociale de l’art (et non seulement institutionnelle ou économique), nourrissant de féconds échanges avec l’histoire littéraire, et intègrent maintenant les théories féministes et postcoloniales, abordant les problématiques du rôle des artistes dans la formation de l’identité nationale ou de la représentation des non-Européens.Thanks to the active collaboration between universities, museums (Tate Britain, Yale Centre for British Art) and research centres (Warburg Institute, Paul Mellon Center), studies on British art from the period between 1750 and 1850 have been remarkably enriched and restructured within the past thirty years (catalogues raisonnés, thematic exhibitions, regular symposiums, research grants). These new directions have made it possible to resituate British artistic production, in particular from the Romantic period, within an international context (especially Italian and German). Not only have formerly forgotten artists (Stubbs, Wright of Derby, Rysbrack…) been brought to light, but, more importantly, approaches have been broadened to include the social history of art (and not only its institutional or economic history) – nourished by fertile exchanges with literary history – and now integrate feminist and postcolonial theory, thus raising questions on the role of artists in the creation of national identity and the representation of non-Europeans.Dank der aktiven Zusammenarbeit von Universitäten, Museen (Tate Britain, Yale Center for British Art) und Forschungszentren (Warburg Institute, Paul Mellon Centre…) hat sich die Forschung im Bereich der britischen Kunst zwischen 1750 und 1850 seit den letzten dreißig Jahren erstaunlich strukturiert und bereichert (Erstellung von Werkverzeichnissen, Organisation von thematischen Ausstellungen, regelmäßigen Symposien und Forschungsstipendien). Diese neuen Orientierungen haben es ermöglicht, die britische Kunstproduktion, besonders die der Romantik, in einen internationalen Zusammenhang (zum Beispiel im Vergleich mit der deutschen und italienischen Kunst) zu setzen. Dabei wurden nicht nur die bis dahin wenig beachteten Künstler (Stubbs, Wright of Derby, Rysbrack…) aufgegriffen, sondern vor allem die Forschungsansätze erweitert. Neben der sozialen Geschichte der Kunst, die über institutionelle und wirtschaftliche Fragen hinaus auch einen ergiebigen Austausch mit der Literaturgeschichte verfolgt, nehmen diese neuen Ansätze mittlerweile auch die feministischen und postkolonialen Theorien auf, die verschiedene Fragestellungen zur Rolle des Künstlers in der Bildung einer nationalen Identität oder zur Darstellung der Nichteuropäer untersuchen.Grazie alla collaborazione attiva fra università, musei (Tate Britain, Yale Center for Britisch Art) e centri di ricerca (Warburg Institute, Paul Mellon Centre…), le ricerche sull’arte britannica fra il 1750 e il 1850 si sono, da una trentina d’anni, notevolmente strutturate e arricchite (elaborazione di cataloghi ragionati, convegni frequenti, borse di ricerca). Questi nuovi orientamenti hanno permesso che la produzione artistica britannica, in particolare quella dell’epoca romantica, prendesse posto nel contesto internazionale (soprattutto italiano e tedesco). Non solamente artisti rimasti nell’ombra (Stubbs, Wright of Derby, Rysbrack…) sono stati studiati, ma soprattutto i diversi approcci si sono estesi alla storia sociale dell’arte (e non solo istituzionale o economica), nutrendo scambi fecondi con la storia della letteratura ; le ricerche integranno, oggi, anche le teorie femministe e postcolonialiste, prendendo in considerazione le problematiche relative al ruolo degli artisti nella formazione dell’identità nazionale o alla rappresentatività dei non Europei.Gracias a una colaboración activa entre universidades, museos (Tate Britain, Yale Center for British Art) y centros de investigaciones (Warburg Institute, Paul Mellon Centre...), la investigación sobre el arte británico entre 1750 y 1850 se ha ido estructurando y enriqueciendo notablemente desde hace unos treinta años (elaboración de catálogos razonados, exposiciones temáticas, simposios regulares, becas de investigación). Estas nuevas orientaciones han permitido la inscripción de la producción artística británica, en particular la del período romántico, dentro del contexto internacional (en particular italiano y alemán). No sólo se estudió a unos artistas hasta en la sombra (Stubbs, Wright of Derby, Rysbrack...) hasta aquel entonces, sino que sobre todo los enfoques se ampliaron a la historia social del arte (y no solamente institucional o económica), generando intercambios fertiles con la historia literaria, e integran ahora las teorías feministas y postcoloniales, abordando la problemática del papel de los artistas en la formación de la identidad nacional o la representación de los no-europeos

An explanation for the isotopic offset between soil and stem water in a temperate tree species

A growing number of field studies report isotopic offsets between stem water and its potential sources that prevent the unambiguous identification of plant water origin using water isotopes. We explored the causes of this isotopic offset by conducting a controlled experiment on the temperate tree species Fagus sylvatica. We measured d2H and d18O of soil and stem water from potted saplings growing on three soil substrates and subjected to two watering regimes. Regardless of substrate, soil and stem water d2H were similar only near permanent wilting point. Under moister conditions, stem water d2H was 11 ± 3 more negative than soil water d2H, coherent with field studies. Under drier conditions, stem water d2H became progressively more enriched than soil water d2H. Although stem water d18O broadly reflected that of soil water, soil stem d2H and d18O differences were correlated (r = 0.76) and increased with transpiration rates indicated by proxies. Soil stem isotopic offsets are more likely to be caused by water isotope heterogeneities within the soil pore and stem tissues, which would be masked under drier conditions as a result of evaporative enrichment, than by fractionation under root water uptake. Our results challenge our current understanding of isotopic signals in the soil plant continuum. © 2020 The Authors. New Phytologist © 2020 New Phytologist TrustThis work was supported by the French national programme EC2CO-Biohefect (RootWater), the French national research agency (projects Hydrobeech, Climbeech and Micromic within the Cluster of Excellence COTE with grant agreement ANR-10-LABX-45; project ORCA with grant agreement ANR-13-BS06-0005-01), the European Research Council (ERC) under the EU Seventh Framework Program (FP7/2007-2013, with grant agreement no. 338264, awarded to LW) and the Aquitaine Region (project Athene with grant agreement 2016-1R20301-00007218). AB also acknowledges an IdEx Bordeaux postdoctoral fellowship from the Universite de Bordeaux (contract no. 22001162)

Evaporation and carbonic anhydrase activity recorded in oxygen isotope signatures of net CO2 fluxes from a Mediterranean soil

The oxygen stable isotope composition (d18O) of CO2 is a valuable tool for studying the gas exchange between terrestrial ecosystems and the atmosphere. In the soil, it records the isotopic signal of water pools subjected to precipitation and evaporation events. The d18O of the surface soil net CO2 flux is dominated by the physical processes of diffusion of CO2 into and out of the soil and the chemical reactions during CO2–H2O equilibration. Catalytic reactions by the enzyme carbonic anhydrase, reducing CO2 hydration times, have been proposed recently to explain field observations of the d18O signatures of net soil CO2 fluxes. How important these catalytic reactions are for accurately predicting large-scale biosphere fluxes and partitioning net ecosystem fluxes is currently uncertain because of the lack of field data. In this study, we determined the d18O signatures of net soil CO2 fluxes from soil chamber measurements in a Mediterranean forest. Over the 3 days of measurements, the observed d18O signatures of net soil CO2 fluxes became progressively enriched with a well-characterized diurnal cycle. Model simulations indicated that the d18O signatures recorded the interplay of two effects: (1) progressive enrichment of water in the upper soil by evaporation, and (2) catalytic acceleration of the isotopic exchange between CO2 and soil water, amplifying the contributions of ‘atmospheric invasion’ to net signatures. We conclude that there is a need for better understanding of the role of enzymatic reactions, and hence soil biology, in determining the contributions of soil fluxes to oxygen isotope signals in atmospheric CO2

Carbon isotope discrimination during branch photosynthesis of Fagus sylvatica: field measurements using laser spectrometry

Photosynthetic carbon isotope discrimination of Fagus sylvatica was measured online and under field conditions using branch bags and laser spectrometers. A substantial variability was observed. Its potential drivers were investigate

Explicitly accounting for needle sugar pool size crucial for predicting intra-seasonal dynamics of needle carbohydrates delta O-18 and delta C-13

We explore needle sugar isotopic compositions (delta O-18 and delta C-13) in boreal Scots pine (Pinus sylvestris) over two growing seasons. A leaf-level dynamic model driven by environmental conditions and based on current understanding of isotope fractionation processes was built to predict delta O-18 and delta C-13 of two hierarchical needle carbohydrate pools, accounting for the needle sugar pool size and the presence of an invariant pinitol pool. Model results agreed well with observed needle water delta O-18, delta O-18 and delta C-13 of needle water-soluble carbohydrates (sugars + pinitol), and needle sugar delta C-13 (R-2 = 0.95, 0.84, 0.60, 0.73, respectively). Relative humidity (RH) and intercellular to ambient CO2 concentration ratio (C-i/C-a) were the dominant drivers of delta O-18 and delta C-13 variability, respectively. However, the variability of needle sugar delta O-18 and delta C-13 was reduced on diel and intra-seasonal timescales, compared to predictions based on instantaneous RH and C-i/C-a, due to the large needle sugar pool, which caused the signal formation period to vary seasonally from 2 d to more than 5 d. Furthermore, accounting for a temperature-sensitive biochemical O-18-fractionation factor and mesophyll resistance in C-13-discrimination were critical. Interpreting leaf-level isotopic signals requires understanding on time integration caused by mixing in the needle sugar pool.Peer reviewe

Temperature‐sensitive biochemical 18^{18}O‐fractionation and humidity‐dependent attenuation factor are needed to predict δ 18^{18}O of cellulose from leaf water in a grassland ecosystem

We explore here our mechanistic understanding of the environmental and physiological processes that determine the oxygen isotope composition of leaf cellulose (δ$^{18}$O$_{cellulose}$) in a drought‐prone, temperate grassland ecosystem. A new allocation‐and‐growth model was designed and added to an $^{18}$O‐enabled soil–vegetation–atmosphere transfer model (MuSICA) to predict seasonal (April–October) and multi‐annual (2007–2012) variation of δ$^{18}$O$_{cellulose}$ and $^{18}$O‐enrichment of leaf cellulose (Δ$^{18}$O$_{cellulose}$) based on the Barbour–Farquhar model. Modelled δ$^{18}$O$_{cellulose}$ agreed best with observations when integrated over c. 400 growing‐degree‐days, similar to the average leaf lifespan observed at the site. Over the integration time, air temperature ranged from 7 to 22°C and midday relative humidity from 47 to 73%. Model agreement with observations of δ$^{18}$O$_{cellulose}$ (R$^{2}$ = 0.57) and Δ$^{18}$O$_{cellulose}$ (R$^{2}$ = 0.74), and their negative relationship with canopy conductance, was improved significantly when both the biochemical $^{18}$O‐fractionation between water and substrate for cellulose synthesis (ε$_{bio}$, range 26–30‰) was temperature‐sensitive, as previously reported for aquatic plants and heterotrophically grown wheat seedlings, and the proportion of oxygen in cellulose reflecting leaf water $^{18}$O‐enrichment (1 – p$_{ex}$p$_{x}$, range 0.23–0.63) was dependent on air relative humidity, as observed in independent controlled experiments with grasses. Understanding physiological information in δ$^{18}$O$_{cellulose}$ requires quantitative knowledge of climatic effects on p$_{ex}$p$_{x}$ and ε$_{bio}$

Unexplained hydrogen isotope offsets complicate the identification and quantification of tree water sources in a riparian forest

We investigated plant water sources of an emblematic refugial population of Fagus sylvatica (L.) in the Ciron river gorges in south-western France using stable water isotopes. It is generally assumed that no isotopic fractionation occurs during root water uptake, so that the isotopic composition of xylem water effectively reflects that of source water. However, this assumption has been called into question by recent studies that found that, at least at some dates during the growing season, plant water did not reflect any mixture of the potential water sources. In this context, highly resolved datasets covering a range of environmental conditions could shed light on possible plant–soil fractionation processes responsible for this phenomenon. In this study, the hydrogen (δ2H) and oxygen (δ18O) isotope compositions of all potential tree water sources and xylem water were measured fortnightly over an entire growing season. Using a Bayesian isotope mixing model (MixSIAR), we then quantified the relative contribution of water sources for F. sylvatica and Quercus robur (L.) trees. Based on δ18O data alone, both species used a mix of top and deep soil water over the season, with Q. robur using deeper soil water than F. sylvatica. The contribution of stream water appeared to be marginal despite the proximity of the trees to the stream, as already reported for other riparian forests. Xylem water δ18O could always be interpreted as a mixture of deep and shallow soil waters, but the δ2H of xylem water was often more depleted than the considered water sources. We argue that an isotopic fractionation in the unsaturated zone and/or within the plant tissues could underlie this unexpected relatively depleted δ2H of xylem water, as already observed in halophytic and xerophytic species. By means of a sensitivity analysis, we found that the estimation of plant water sources using mixing models was strongly affected by this δ2H depletion. A better understanding of what causes this isotopic separation between xylem and source water is urgently needed.</p

Do 2H and 18O in leaf water reflect environmental drivers differently?

We compiled hydrogen and oxygen stable isotope compositions (δ H and δ O) of leaf water from multiple biomes to examine variations with environmental drivers. Leaf water δ H was more closely correlated with δ H of xylem water or atmospheric vapour, whereas leaf water δ O was more closely correlated with air relative humidity. This resulted from the larger proportional range for δ H of meteoric waters relative to the extent of leaf water evaporative enrichment compared with δ O. We next expressed leaf water as isotopic enrichment above xylem water (Δ H and Δ O) to remove the impact of xylem water isotopic variation. For Δ H, leaf water still correlated with atmospheric vapour, whereas Δ O showed no such correlation. This was explained by covariance between air relative humidity and the Δ O of atmospheric vapour. This is consistent with a previously observed diurnal correlation between air relative humidity and the deuterium excess of atmospheric vapour across a range of ecosystems. We conclude that H and O in leaf water do indeed reflect the balance of environmental drivers differently; our results have implications for understanding isotopic effects associated with water cycling in terrestrial ecosystems and for inferring environmental change from isotopic biomarkers that act as proxies for leaf water