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Aim The aim was to decipher Europe‐wide spatio‐temporal patterns of forest growth dynamics and their associations with carbon isotope fractionation processes inferred from tree rings as modulated by climate warming. Location Europe and North Africa (30‒70° N, 10° W‒35° E). Time period 1901‒2003. Major taxa studied Temperate and Euro‐Siberian trees. Methods We characterize changes in the relationship between tree growth and carbon isotope fractionation over the 20th century using a European network consisting of 20 site chronologies. Using indexed tree‐ring widths (TRWi), we assess shifts in the temporal coherence of radial growth across sites (synchrony) for five forest ecosystems (Atlantic, boreal, cold continental, Mediterranean and temperate). We also examine whether TRWi shows variable coupling with leaf‐level gas exchange, inferred from indexed carbon isotope discrimination of tree‐ring cellulose (Δ13Ci). Results We find spatial autocorrelation for TRWi and Δ13Ci extending over a maximum of 1,000 km among forest stands. However, growth synchrony is not uniform across Europe, but increases along a latitudinal gradient concurrent with decreasing temperature and evapotranspiration. Latitudinal relationships between TRWi and Δ13Ci (changing from negative to positive southwards) point to drought impairing carbon uptake via stomatal regulation for water saving occurring at forests below 60° N in continental Europe. An increase in forest growth synchrony over the 20th century together with increasingly positive relationships between TRWi and Δ13Ci indicate intensifying impacts of drought on tree performance. These effects are noticeable in drought‐prone biomes (Mediterranean, temperate and cold continental). Main conclusions At the turn of this century, convergence in growth synchrony across European forest ecosystems is coupled with coordinated warming‐induced effects of drought on leaf physiology and tree growth spreading northwards. Such a tendency towards exacerbated moisture‐sensitive growth and physiology could override positive effects of enhanced leaf intercellular CO2 concentrations, possibly resulting in Europe‐wide declines of forest carbon gain in the coming decades. Spanish Government, Grant/Award Number: AGL2015‐68274 ‐C3 ‐3‐R; Sixth Framework Programme, Grant/AwardNumber: EVK2‐2001 ‐00237; Seventh Framework Programme, Grant/AwardNumber: COST ‐STSM ‐ECOST ‐STSM ‐FP1304‐140915‐066395 and ERANET‐Mundus program (Grant agreement 20112573)

Researchers have increasingly recognised a profound need for more information on SOC stocks in the soil and the factors governing their stability and dynamics. Many questions still remain unanswered about the interplay between changes in plant communities and the extent to which changes in aboveground productivity affect the carbon dynamics in soils through changes in its quantity and quality. Therefore, the main aim of this research was to examine the SOC accumulation potential of semi-natural grasslands of different productivities and determine the distribution of SOM fractions over varying soil depth intervals (0-10, 10-20, 20-30 30-50 50-80 and 80+cm). SOM fractionation was considered as a relative measure of stability to separate SOM associated with clay minerals from SOM of specific light densities less than 2 g cm(-3) (size-density fractionation). Two clay-associated fractions (CF1

The dynamics of radial growth of pine (Pinus sylvestris L.) and spruce (Picea obovata Ledeb.) trees at the northern limit of their distribution in the area of the Kola Peninsula affected by emissions from the Severonikel industrial complex has been investigated. A correlation between the radial growth of trees and a combination of environmental factors has been revealed through the use of statistical methods, and a contribution of individual factors has been identified. Statistically significant correlations between the productivity of trees, on one hand, and the level of pollution, topography, and climatic effects, on the other, have been detected. A significant correlation between the degree of tree growth and the amount of industrial emissions in the atmosphere has been revealed; the correlation depended on the degree of technogenic impact on the trees, the tree species, and the location of trees on hill slopes. The growth oscillations of different frequencies (long waves of 50 years, medium-length waves of 30 years, and short annual waves) were shown to depend on climatic factors in different ways.

Recently published, improved chronologies for volcanic sulfate in Greenland and Antarctic ice permit a comparison of the growth responses of absolutely annually dated tree rings at three locations in Siberia with annual ice-core records of volcanic eruptions centered on AD 536. For the first time for this region and period, we present unique data sets for tree-ring width, cell-wall thickness, δ13C and δ18O in cellulose. These were based on multiple samples from relict wood of larch obtained from two sites close to the northern limit of tree growth on the Taimyr Peninsula and in northeastern Yakutia, and at a high-elevation, location 20° further South in the Altai Mts. An event in AD 536 was associated with different, but marked, changes in tree-ring parameters at the high-latitude sites compared with the high elevation site. An AD 541 event was associated with its own distinctive tree-ring responses across the three sites and multiple variables. The years after AD 532 were marked by a strong and sustained decrease in growth at the high-elevation, more southerly, site. The combination of improved ice-core chronology for the climatically effective volcanic eruptions of this part of the 6th century AD, and an array of tree-ring sites with different climates and multiple tree-ring variables permits a richer description of tree responses to this cluster of events. The pattern of tree-ring parameter responses at the three locations in AD 536, AD 541, and perhaps AD 532 is consistent with responses to climatically effective volcanic eruptions influencing tree response in those and subsequent years.

The increasing carbon dioxide (CO2) concentration in the atmosphere in combination with climatic changes throughout the last century are likely to have had a profound effect on the physiology of trees: altering the carbon and water fluxes passing through the stomatal pores. However, the magnitude and spatial patterns of such changes in natural forests remain highly uncertain. Here, stable carbon isotope ratios from a network of 35 tree-ring sites located across Europe are investigated to determine the intrinsic water-use efficiency (iWUE), the ratio of photosynthesis to stomatal conductance from 19012000. The results were compared with simulations of a dynamic vegetation model (LPX-Bern 1.0) that integrates numerous ecosystem and landatmosphere exchange processes in a theoretical framework. The spatial pattern of tree-ring derived iWUE of the investigated coniferous and deciduous species and the model results agreed significantly with a clear south-to-north gradient, as well as a general increase in iWUE over the 20th century. The magnitude of the iWUE increase was not spatially uniform, with the strongest increase observed and modelled for temperate forests in Central Europe, a region where summer soil-water availability decreased over the last century. We were able to demonstrate that the combined effects of increasing CO2 and climate change leading to soil drying have resulted in an accelerated increase of iWUE. These findings will help to reduce uncertainties in the land surface schemes of global climate models, where vegetationclimate feedbacks are currently still poorly constrained by observational data.

Tree-ring oxygen stable isotope data series from conifers growing on the Dachstein Plateau (Austrian Alps) were selected to demonstrate the applicability of the serial pooling method using shifted 5-year tree-ring blocks for summer temperature reconstruction. The addressed method allows the construction of long isotope chronologies with significant climate correlation and well preserved climate sensitivity applying the irreducible sample replication of five trees. The linear regression model for temperature reconstruction is verifiable and the predicted data are well correlated with instrumental data, especially reproducing the long-term temperature trend. However, the reduced mean variance leads to loss of extreme years, which can be regulated by the combination of one data series in annual resolution with five shifted 5-year block data series. This significantly improves the variance of the mean chronology, sufficiently to identify extremes. Therefore, we recommend the use of mixed data sets as a compromise between essential sample replication and economic considerations.

Summary It is known that crop residue input has a strong impact on the quantity of soil organic matter (SOM). However, its influence on SOM quality is often unknown. The effect of organic matter (OM) input on soil organic carbon (SOC) and functional SOC pools was investigated in a Chinese long-term double-cropping experiment with rice. It could be demonstrated that the C content of hot-water soil extracts (CHWE )m ay serve as an indicator of the decomposable SOC pool. A particle size–density fractionation was used to separate SOC pools with different interactions with the mineral soil matrix. The hot-water C extractability of different particle size-density fractions, together with their δ 13 C isotopic signatures, was applied to differentiate stability and potential degradability of SOC pools. The main findings were: first, the input of OM (rice straw + animal manure + green manure) to the unfertilized (Nil) and fertilized (NPK) treatments resulted in a 43–64% increase of SOC over 14 years. Second, during the same period the CHWE pool declined by 25–32% in plots without OM input. Organic amendments reduced the decrease in the CHWE pool by about 50%. Hot-water-extractable carbon (C) (CHWE) of bulk soil could serve as an indicator of decomposable SOC pools with the potential for nutrient supply during decomposition. Third, the importance and capacity of smaller-sized clay particles (CF1

Stable isotope chronologies of carbon and oxygen for the period from 1600 to 2003 and of non-exchangeable hydrogen for the last century were constructed base upon tree-ring latewood cellulose from oaks (Quercus petraea Matt. Liebl.) grown in the Vienna region (Austria). The stable isotope ratios reflect highly significantly the summer climate conditions. For the reconstruction of temperature and relative air humidity, verifiable bivariate linear regression models were calculated. Hydrogen isotope values clearly enhanced the model verification. The reconstruction of July relative air humidity in the region Vienna (Austria) for the last 400 years was carried out with carbon and oxygen stable isotope ratios. During this period the humidity oscillated around a mean of 74.7 ± 4.4% with wet and dry periods in a cycle of approximately 130 years. Predominant wet conditions were reconstructed for the periods 1690–1710, 1765–1820 and 1900–1960, predominant dry periods for 1715 to 1730, 1830 to 1870 and from approximately 1960 to present. Extreme wet months of July were identified in the years 1663, 1795, 1816, 1906, 1915 and 1926, exceptionally dry were inferred for 1616, 1636, 1637, 1751, 1822, 1857, 1863, 1990, 1992 and 2001.

This study presents a new pine (Pinus sylvestris L.) ring-width chronology and a summer temperature reconstruction for the last 400 years from the Khibiny Low Mountains (Kola Peninsula, NW Russia). Pine trees from sites at the altitudinal timberline of Khibiny Mountains show pronounced climatic signals in tree-ring width. We found a strong positive correlation with summer temperature of July–August (r = 0.58). The reconstruction shows lower summer temperatures from a.d. 1630 to 1840, a subsequent warming up to the mid-20th century and a cooling trend afterwards. According to our data, a temperature increase is observed during the past decade. The good coherence of multi-decadal to secular trends of our reconstruction and series of observed solar activity indicate that solar activity may have been one major driving factor of past climate on Kola Peninsula.

The 7 m thick sediment profile at Plinz in northern Thuringia (central Germany) covering the time span between 10,000 and at least 8000 14C years BP (about 11,600–9000 cal BP) was studied using radiocarbon, stable isotopes and pollen analysis. The results reflect the very fast climatic transition from the Late Glacial to the Holocene as a change from cold and dry to warmer and wetter conditions. A short climatic deterioration during the Preboreal oscillation (PBO) at around 9800 14C years BP is clearly reflected by a sharp drop in the Pinus concentration accompanied by a considerable increase in Betula, Salix, various herbs and the distinct occurrence of aquatic plants. During the Preboreal stable isotopes of biogenic carbonate show several episodes with altered levels of atmospheric moisture. Continuous climatic improvement without any oscillations can be suggested for the period covering the end of Preboreal and the Boreal.

The study presents a new serial pooling method of shifted tree ring blocks for the building of isotope chronologies. This method combines the advantages of traditional 'serial' and 'intertree' pooling, and can be recommended for the construction of sub-regional long isotope chronologies with sufficient replication, and on annual resolution, especially for the case of extremely narrow tree rings. For Scots pines (Pinus sylvestris L., Khibiny Low Mountains, NW Russia) and Silver firs (Abies alba Mill., Franconia, Southern Germany), serial pooling of five consecutive tree rings seems appropriate because the species- and site-specific particularities lead to blurs of climate linkages in their tree rings for the period up to ca. five years back. An equivalent to a five-year running means that curve gained on the base annual data sets of single trees can be derived from the analysis of yearly shifted five-year blocks of consecutive tree rings, and therefore, with approximately 20% of the expense. Good coherence of delta(13)C- and delta(18)O-values between calculated means of annual total rings or late wood data and means of five-year blocks of consecutive total tree rings analysed experimentally on most similar material confirms this assumption.

The carbon isotope composition (delta(13)C, per thousand) and discrimination (Delta, per thousand) of old grown North American Pinus ponderosa Dougl. Ex P. et C. Laws. and European Pinus sylvestris L. were determined using trees grown under almost identical growing conditions in a mixed stand in Bralitz, Northeast Germany. Single-tree delta(13)C analyses of tree-ring cellulose of both species were carried out at a yearly resolution for the period 1901-2001 and the results compared with growth (basal area increment). Annual mean delta(13)C values for P. ponderosa ranged from-21.6 per thousand to-25.2 per thousand and for P. sylvestris from-21.4 per thousand to-24.4 per thousand. Accordingly, (13)C discrimination (Delta) showed higher values for P. ponderosa throughout the investigation period. Five characteristic periods of Delta were identified for both the tree species, reflecting positive and negative influences of environmental factors. Good growing conditions such as after-thinning events had a positive effect on Delta, reflecting higher values, while poor conditions like aridity and air pollution had a negative influence, reflecting lower values. The dynamics of Delta were likewise reflected in the growth (basal area increment, BAI). Higher (13)C discrimination values of P. ponderosa led to higher BAIs of P. ponderosa in comparison with P. sylvestris. Correlation function analyses confirmed that P. sylvestris was more dependent on precipitation than P. ponderosa, which showed a closer relationship with temperature. The results confirm that under predominantly dry growing conditions, P. ponderosa showed better growth performance than P. sylvestris, indicating better common intrinsic water-use efficiency and, therefore, higher rates of net photosynthesis at a given transpiration. In view of the prospect of climate change, the results are very significant for assessing both trees' physiological properties and, hence, their potential for coping with future growing conditions.

The determination of isotope ratios of non-exchangeable hydrogen in tree-ring cellulose is commonly based on the nitration of wood cellulose followed by online high-temperature pyrolysis and isotope ratio mass spectrometry measurement of cellulose nitrate samples. The application of this method requires a proper calibration using appropriate reference materials whose delta(2)H values have been reliably normalized to the V-SMOW/SLAP scale. In our study, we achieve this normalization by a direct alternating measurement of reference waters (V-SMOW and SLAP) and three cellulose nitrates chosen as reference materials. For that purpose, both water and solid organic samples are introduced into the pyrolysis reactor by silver capsule injection. The analytical precision of the water measurement using the capsule method is +/-1.5 per thousand. The hydrogen isotopic composition of three cellulose nitrate standards measured ranges from -106.7 to -53.9 per thousand. The standard deviation of the calculated means from five measurement periods of those standards is better than 1 per thousand. Twenty-four different measurements of the hydrogen isotope composition of cellulose nitrate were evaluated in order to assess the precision of the described method. We obtained an analytical precision of +/-3.0 per thousand as representative for the 95% confidence interval applicable for routine measurements of cellulose nitrate samples. Evidence was found for significant differences in the behavior of cellulose nitrate and PE foil during the pyrolitic conversion that emphasizes the need for a proper calibration of the routine measurements. This calibration can only be successful if the reference materials used have a very similar chemical composition and undergo the same preparation procedure as the samples.

Considering the combined effects of CO2 fertilization and climate change drivers on plant physiology leads to a modest increase in simulated European forest transpiration in spite of the effects of CO2-induced stomatal closure. The Earth’s carbon and hydrologic cycles are intimately coupled by gas exchange through plant stomata1,2,3. However, uncertainties in the magnitude4,5,6 and consequences7,8 of the physiological responses9,10 of plants to elevated CO2 in natural environments hinders modelling of terrestrial water cycling and carbon storage11. Here we use annually resolved long-term δ13C tree-ring measurements across a European forest network to reconstruct the physiologically driven response of intercellular CO2 (Ci) caused by atmospheric CO2 (Ca) trends. When removing meteorological signals from the δ13C measurements, we find that trees across Europe regulated gas exchange so that for one ppmv atmospheric CO2 increase, Ci increased by ∼0.76 ppmv, most consistent with moderate control towards a constant Ci/Ca ratio. This response corresponds to twentieth-century intrinsic water-use efficiency (iWUE) increases of 14 ± 10 and 22 ± 6% at broadleaf and coniferous sites, respectively. An ensemble of process-based global vegetation models shows similar CO2 effects on iWUE trends. Yet, when operating these models with climate drivers reintroduced, despite decreased stomatal opening, 5% increases in European forest transpiration are calculated over the twentieth century. This counterintuitive result arises from lengthened growing seasons, enhanced evaporative demand in a warming climate, and increased leaf area, which together oppose effects of CO2-induced stomatal closure. Our study questions changes to the hydrological cycle, such as reductions in transpiration and air humidity, hypothesized to result from plant responses to anthropogenic emissions.

The microwave technique is found to be very applicable for the preparation of alpha-cellulose from wood samples and can be recommended for analyzing the stable carbon isotopes in tree rings. At a reaction temperature of 80 degrees C, the extraction time can be decreased from 36 h to 15 min. Microwave-supported prepared cellulose contains more amorphous constituents, resulting in a relatively higher reactivity and amenability for a following nitration with regard to determination of nonexchangeable hydrogen. The delta18O values of microwave-enhanced extracted cellulose remain significantly lighter than reference values, possibly as a result of an increased oxygen isotope exchange between bleaching solution and cellulose under conditions of high energy input. Therefore, this technique cannot be recommended for oxygen isotope analyses in wood cellulose.

α-Cellulose was isolated from four samples of Scots pine (Pinus sylvestris L.). Each sample was divided into two portions. One portion had the resins removed by solvent extraction prior to removal of lignins by treatment with acidic sodium chlorite solution and treatment with sodium hydroxide solution to remove hemicelluloses. The other portion was processed in the same way apart from the solvent extraction step. The isolated wood constituents were characterised by attenuated total reflectance Fourier transform infrared (ATR/FT-IR) spectroscopy. The infrared spectra of the resulting α-cellulose samples were identical indicating that treatment with acidic sodium chlorite and sodium hydroxide was sufficient to remove resins. The values of the stable isotope ratios (carbon, oxygen and hydrogen) for each pair of α-cellulose sub-samples also showed no significant differences within the reproducibility of the methods. The implication of these studies demonstrate that the customary step of resin extraction from pine is unnecessary if sodium chlorite and sodium hydroxide are used for the isolation of α-cellulose following the technique described in this paper. In addition, the study demonstrates that the oxygen isotope ratio of the water used for cellulose extraction does not influence the stable isotope values in the α-cellulose obtained. The importance of isotopic homogeneity within the cellulose sample is also highlighted.

Combined investigations of ostracod communities, pollen, and stable isotopes were carried out on Lateglacial limnic high-resolution sediment sequence from Miesenheim in Germany. The pollen data confirm the presence of Meiendorf Interstadial, the first interstadial after the Pleniglacial. The former shallow lake was formed at the end of the Pleniglacial and partly dried out between the Bolling and the Allerod. Lake Laach tephra (12,880 warve yr BP) marks the top of this profile. The intensive colonization with ostracods at the beginning of the Meiendorf Interstadial is characterized by great instability of their populations. Only ostracods from the upper littoral zones of lakes, ponds or temporary pools were found. The stable isotope data (δ18O, δ13C) of the valves of the Cypridopsis vidua, Herpetocypris reptans, and Candona candida reflect the different microhabitats of these three species and show a general climatic development during the Meiendorf Interstadial with two summer temperature peaks, one at the beginning and a weaker one in the second half of the Meiendorf Interstadial.

Data obtained from the low-elevation Khibiny Mountains (ca. 67–68jN; 33–34jE) on the Kola Peninsula, northwest Russia, indicate a period of exceptionally warm and dry conditions commenced at ca. AD 600 and was most pronounced between ca. AD 1000 and 1200. Warmer summer temperatures during this period (coeval with the ‘Medieval Warm Period’ observed in other parts of Europe) are evident in a 100–140 m upward shift in the pine (Pinus sylvestris L.) limit in the Khibiny Mountains. On average, the cellulose of pine trees that grew between ca. AD 1000 and 1300 is enriched by y 13 C values of around 1xcompared to the modern trees from the region, further suggesting warmer summer climate than at present. The Medieval Warm Period was also accompanied by a steady decline in avalanche activity and the resulting formation of soils on the current avalanche cones in the Khibiny Mountains, suggesting lower winter precipitation and thinner snow cover. Lower precipitation is also evident by currently submerged tree stumps dating to the medieval period that indicate lower lake levels on the Kola Peninsula. In the middle of the peninsula at about AD 1000, the level of small closed-basin lakes was f1 m lower than the modern time at some sites. Drier conditions may be attributable to decreased cyclonic activity. The medieval warm and dry episode was followed at ca. AD 1300 by the development of a colder climate with increased precipitation resulting in a decline in the alpine pine limits, increased avalanche activity, and higher lake levels. That phase corresponds to the modern aeolian episode reconstructed in subarctic Finland. Our results indicate that the Medieval Warm Period on the Kola Peninsula

A set of 40 subfossil Scots pines (Pinus sylvestris L.) was sampled in small lakes beyond the modernpine limit in the northwest Kola Peninsula, Russia. Radiocarbon dating suggests that the pine expanded north of its present-day limit between 7000 and 3500yr BP. The most extensive occurrence of pine forests was reconstructed between 6250 and 5750 yr BP. Numerous samples collected from trunks and stubs in situ clearly indicate lower lake levels between 6200 and 4400 yr BP. Living and14C dated subfossil pine samples were analysed for the mean carbon, oxygen and hydrogen stable isotope composition of their wood cellulose. The mean δ13C, δ18O and δ2H values of the wood samples from the mid-Holocene time are C. 1.1%, 0.9% and lock, respectively - more positive than those of living trees in this region. These results suggest that the mid-Holocene climate in the region was warmer and drier than nowadays. The data agree with previous palynological, macrofossil and limnological studies from northernmost Fennoscandia. During the late-Holocene climatic deterioration after c. 3500 yr BP, the decline of the northern pine limit was synchronous with other parts of northern Eurasia. Comparison with dated pine series from the north-central Kola Peninsula and Finnish Lapland suggests that the decline of the northernmost pine limit in the eastern part of the area may have occurred somewhat earlier than in the western part.

The climate sensitivity of carbon (δ(13)C), oxygen (δ(18)O) and hydrogen (δ(2)H) isotope signatures in tree-ring cellulose of Abies alba Mill. from a marginally industrialized area of Franconia (Germany) was analysed for the last 130 years. All isotopes preserve climatic signals up to c. 1950 AD. After 1950 we observe a clear reduction in climate sensitivity of δ(13)C and δ(2)H while δ(18)O - climate relations remain well pronounced. Nevertheless statistical tests implied that SO2 background emissions of West Germany had influenced isotope signatures long before 1950. The relationships between isotope values and concentrations of SO2, dust, O3 and NO2 at the regional level during the period 1979-2006 indicate that δ(13)C and δ(18)O were influenced primarily by SO2. The impact of SO2 on δ(2)H was negligible, but the observed reduction of climate sensitivity may be caused by synergic influences. The results have significant implications if isotope signatures from tree-rings from anthropogenic influenced regions are used to reconstruct past climate.

Combining nine tree growth proxies from four sites, from the west coast of Norway to the Kola Peninsula of NW Russia, provides a well replicated (> 100 annual measurements per year) mean index of tree growth over the last 1200 years that represents the growth of much of the northern pine timberline forests of northern Fennoscandia. The simple mean of the nine series, z-scored over their common period, correlates strongly with mean June to August temperature averaged over this region ( r = 0.81), allowing reconstructions of summer temperature based on regression and variance scaling. The reconstructions correlate significantly with gridded summer temperatures across the whole of Fennoscandia, extending north across Svalbard and south into Denmark. Uncertainty in the reconstructions is estimated by combining the uncertainty in mean tree growth with the uncertainty in the regression models. Over the last seven centuries the uncertainty is < 4.5% higher than in the 20th century, and reaches a maximum of 12% above recent levels during the 10th century. The results suggest that the 20th century was the warmest of the last 1200 years, but that it was not significantly different from the 11th century. The coldest century was the 17th. The impact of volcanic eruptions is clear, and a delayed recovery from pairs or multiple eruptions suggests the presence of some positive feedback mechanism. There is no clear and consistent link between northern Fennoscandian summer temperatures and solar forcing.

BackgroundCarbon isotope data from conifer trees play an important role in research on the boreal forest carbon reservoir in the global carbon cycle. Carbon isotopes are routinely used to study interactions between the environment and tree growth. Moreover, carbon isotopes became an essential tool for the evaluation of carbon assimilation and transport from needles into reserve pools, as well as the allocation of stored assimilates within a tree. The successful application and interpretation of carbon isotopes rely on the coherence of isotopic fractionation modeling. This study employs a new Carbon Metabolism Oscillatory Model (CMOM) to interpret the experimental data sets on metabolic seasonal dynamics of13C/12 C and18O/16O ratios measured in twig components of Scots pine growing in southern Siberia (Russia).ResultsThe dynamics of carbon isotopic variables were studied in components ofPinus sylvestrisL. in light and in dark chambers during the vegetation period from 14 June to 28 July 2006. At the beginning of this period water-soluble organic matter, mostly labile sugars (including sucrose as the main component) and newly formed bulk needle material, displayed relatively “light” δ13C values (depletion in13 C). Then,13 C content increased again with noticeable “depletion” events in the middle of the growth period. A gradual13 C accumulation took place in the second half of the vegetation period. Similar effects were observed both in the light and in the dark with some temporal shifts. Environmental factors did not influence the δ13C values. A gradual12C-depletion effect was noticed in needles of the previous year. The δ13C values of sucrose and proteins from needle biomass altered independently from each other in the light chamber. A distinct negative correlation between δ13C and δ18O values was revealed for all studied variables.ConclusionsThe abrupt13C depletion recorded by all tested trees for the period from June to July provides clear evidence of the transition from the dominant role of reserve carbohydrate pool (RCP) during the first half of the growth season to the preferable current year carbohydrate pool (CCP) consumption by new needles during its second half. The investigation of the isotopic signatures ofPinus sylvestrisL. emphasizes the pivotal role of the intra-seasonal dynamics in carbon metabolism through the transport of assimilates from autotrophic (needles) to heterotrophic (twigs) organs of the studied trees. This provides an explanation for changes of carbon isotopic values observed within the growth season. The CMOM-based results support the hypothesis of the integration of three carbohydrate pools by photosynthesizing cells. The fluctuations of the carbon isotope ratios in different carbohydrate pools underlie various physiological processes in the tree metabolism. The possible mechanisms and pathways of formation of these carbohydrate pools are further discussed. Hence, CMOM provides a reasonable explanation for the absence of the impact of environmental conditions on the needle isotopic variables, the12C-depletion effects and the use of RCP in needles. The model explains the negative connections between δ13C and δ18O values in all studied variables.

International audience; Changes in maximum spring and summer temperature are expected to have impacts on plant phenology and the occurrence of forest fires. Homogenised instrumental records of maximum spring and summer temperature are available in northern France for the past century, as well as documentary records of grape harvest dates and forest fire frequencies. Here we provide a new proxy of seasonal climate obtained by the analysis of latewood tree ring cellulose isotopic composition (δ18O, δ13C and δD), from 15 living oak trees (Quercus petraea) sampled in the Fontainebleau forest, near Paris. For the past 30 years, we have conducted a study on the inter-tree (for oxygen isotopes) and inter-station (for oxygen and hydrogen)isotopic variability. Multiple linear regression statistical analyses are used to assess the response function of documentary and tree-ring isotopic records to a variety of climatic and hydrological parameters. This calibration study highlights the correlation between latewood tree-ring δ18O and δ13C, grape harvest dates and numbers of forest fire starts with maximum growing season (April to September) temperature, showing the potential of multiple proxy reconstructions to assess the past fluctuations of this parameter prior to the instrumental period.

We present the first European network of tree ring delta(13)C and delta(18)O, containing 23 sites from Finland to Morocco. Common climate signals are found over broad climatic-ecological ranges. In temperate regions we find positive correlations with summer maximum temperatures and negative correlations with summer precipitation and Palmer Drought Severity Indices (PDSI) with no obvious speciesspecific differences. Regional delta(13)C and delta(18)O chronologies share high common variance in year-to-year variations. Long-term variations, however, exhibit differences that may reflect spatial variability in environmental forcings, age trends and/or plant physiological responses to increasing atmospheric CO(2) concentration. Rotated principal component analysis (RPCA) and climate field correlations enable the identification of four sub-regions in the delta(18)O network - northern and eastern Central Europe, Scandinavia and the western Mediterranean. Regional patterns in the delta(13)C network are less clear and are timescale dependent. Our results indicate that future reconstruction efforts should concentrate on delta(18)O data in the identified European regions.

Publisher Summary The last four interglacials (intervals during which global ice volume was similar to, or less than, that of our current warm stage) correspond to the warmest parts of the marine oxygen isotope stages marine isotopic age (MIS) 5, 7, 9, and 11. These interglacials followed the 100-kyr rhythm of eccentricity, but each had different insolation regimes, different durations, different ice volumes, and different sea-level heights. However, atmospheric greenhouse gas concentrations were similar and reached values, which, largely, were close to those of the current interglacial (Holocene or MIS 1) before the industrial revolution led to the artificial enrichment of the atmosphere's greenhouse gas concentrations via the burning of fossil fuels. This chapter summarizes the state of knowledge on each of the climatic warm intervals.

An improved method for the determination of deuterium-to-hydrogen (D/H) ratios of non-exchangeable hydrogen in cellulose is presented. The method is based on the equilibration reaction of the hydroxyl hydrogen of cellulose and water vapour of known isotopic composition. The equilibrated cellulose is pyrolysed and the total D/H ratio determined by subsequent online isotope ratio mass spectrometry (IRMS). With a mass balance system the D/H ratio of non-exchangeable hydrogen is recalculated after an empirical calibration has been performed, yielding a mean exchangeability of 0.239 and an equilibrium fractionation factor of 1.082 between the hydroxyl hydrogen of cellulose and water hydrogen at 110 degrees C. Equilibration takes 10 min per sample. Results obtained by this online equilibration method agree very well with values obtained by the nitration technique (R2 = 0.941). The uncertainty of the equilibration method is +/-4 per thousand resulting from a single standard deviation of +/-2.8 per thousand for the equilibration determined by standard cellulose and 2.8 per thousand from the variable exchangeability of the hydroxyl hydrogen in cellulose due to crystalline areas. The latter uncertainty may be lowered by minimising the crystallinity of the cellulose. Advantages of this new technique are (i) the considerably reduced sample amount required (as low as 0.2 mg, ideally 0.5 mg compared with 20 mg for the conventional nitration technique); (ii) an approximately 100-fold reduced process time; and (iii) no need for the hazardous chemicals used in the nitration technique.