bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of temperature, salinity and growth rate on the stable hydrogen isotopic composition of long chain alkenones produced by Emiliania huxleyi and Gephyrocapsa oceanica
Authors: Schouten S. , Ossebaar J. , Schreiber K. , Kienhuis M. V. M. , Langer G. , Benthien A. , Bijma J.
Published: April 2010

Abstract. Two haptophyte algae, Emiliania huxleyi and Gephyrocapsa oceanica, were cultured at different temperatures and salinities to investigate the impact of these factors on the hydrogen isotopic composition of long chain alkenones synthesized by these algae. Results showed that alkenones synthesized by G. oceanica were on average depleted in D by 30 compared to those of E. huxleyi when grown under similar temperature and salinity conditions. The fractionation factor, αalkenones-H2O, ranged from 0.760 to 0.815 for E. huxleyi and from 0.741 to 0.788 for G. oceanica. There was no significant correlation of αalkenones-H2O with temperature but a positive linear correlation was observed between αalkenones-H2O and salinity with ~3 change in fractionation per salinity unit and a negative correlation between αalkenones-H2O and growth rate. This suggests that both salinity and growth rate can have a substantial impact on the stable hydrogen isotopic composition of long chain alkenones in natural environments.
C2-C10 hydrocarbon emissions from a boreal wetland and forest floor
Authors: Hellén H. , Hakola H. , Pystynen K.-H. , Rinne J. , Haapanala S.
Published: April 2010

Abstract. Emissions of various C2-C10 hydrocarbons (VOCs) and halogenated hydrocarbons (VHOCs) from a boreal wetland and a Scots pine forest floor in south-western Finland were measured by the static chamber technique. Isoprene was the main non-methane hydrocarbon emitted by the wetland, but small emissions of ethene, propane, propene, 1-butene, 2-methylpropene, butane, pentane and hexane were also detected. The isoprene emission from the wetland was observed to follow the commonly-used isoprene emission algorithm. The mean emission potential of isoprene was 224 µg m-2 h-1 for the whole season. This is lower than the emission potentials published earlier; that is probably at least partly due to the cold and cloudy weather during the measurements. No emissions were detected of monoterpenes or halogenated hydrocarbons from the wetland. The highest hydrocarbon emissions from the Scots pine forest floor were measured in spring and autumn. However, only a few measurements were conducted during summer. The main compounds emitted were monoterpenes. Isoprene emissions were negligible. The total monoterpene emission rates varied from zero to 373 µg m-2 h-1. The results indicated that decaying plant litter may be the source for these emissions. Small emissions of chloroform (100-800 ng m-2 h-1), ethene, propane, propene, 2-methylpropene, cis-2-butene, pentane, hexane and heptane were detected. Comparison with Scots pine emissions showed that the forest floor may be an important monoterpene source, especially in spring.
DMS cycle in the marine ocean-atmosphere system – a global model study
Authors: Kloster S. , Feichter J. , Maier-Reimer E. , Six K. D. , Stier P. , Wetzel P.
Published: April 2010

Abstract. A global coupled ocean-atmosphere modeling system is established to study the production of dimethylsulfide (DMS) in the ocean, the DMS flux to the atmosphere, and the resulting sulfur concentrations in the atmosphere. The DMS production and consumption processes in the ocean are simulated in the marine biogeochemistry model HAMOCC5, embedded in a ocean general circulation model (MPI-OM). The atmospheric model ECHAM5 is extended by the microphysical aerosol model HAM, treating the sulfur chemistry in the atmosphere and the evolution of the microphysically interacting internally- and externally mixed aerosol populations. We simulate a global annual mean DMS sea surface concentration of 1.8 nmol l−1, a DMS emission of 28 Tg(S) yr−1, a DMS burden in the atmosphere of 0.077 Tg(S), and a DMS lifetime of 1.0 days. To quantify the role of DMS in the atmospheric sulfur cycle we simulate the relative contribution of DMS-derived SO2 and SO42− to the total atmospheric sulfur concentrations. DMS contributes 25% to the global annually averaged SO2 column burden. For SO42− the contribution is 27%. The coupled model setup allows the evaluation of the simulated DMS quantities with measurements taken in the ocean and in the atmosphere. The simulated global distribution of DMS sea surface concentrations compares reasonably well with measurements. The comparison to SO42− surface concentration measurements in regions with a high DMS contribution to SO42− shows an overestimation by the model. This overestimation is most pronounced in the biologically active season with high DMS emissions and most likely caused by a too high simulated SO42− yield from DMS oxidation.
Comparison of modelled and monitored deposition fluxes of sulphur and nitrogen to ICP-forest sites in Europe
Authors: Simpson D. , Fagerli H. , Hellsten S. , Knulst J. C. , Westling O.
Published: April 2010

Abstract. The EMEP MSC-W Eulerian chemical transport model, and its predictions of deposition of acidifying and eutrophying pollutants over Europe, play a key role in the development of emission control strategies for Europe. It is important that this model is tested against observational data. Here we compare the results of the EMEP model with measured data from 160 sites of the European Union/ICP Forest (Level II) monitoring network, for the years 1997 and 2000. This comparison comprises: (a) Precipitation amount, (b) Total deposition of SO2−4 to coniferous and deciduous forests, (c) Wet deposition of SO2−4, NO3− and NH4+ in open field sites, and (d) Concentrations of SO2−4, NO3− and NH4+ in precipitation. Concerning precipitation, the EMEP model and ICP network showed very similar overall levels (within 4% for 1997 and 11% for 2000). The correlation was, however, poor (r2=0.15–0.23). This can be attributed largely to the influence of a few outliers, combined with a small range of rainfall amounts for most points. Correlations between modelled and observed deposition values in this study were rather high (r2 values between 0.4–0.8 for most components and years), with mean values across all sites being within 30%. The EMEP model tends to give somewhat lower values for SO2−4, NO3− and NH4+ wet deposition to ICP, but differences in mean values were within 20% in 1997 and 30% in 2000. Modelled and observed concentrations of SO2−4, NO3− and NH4+ in precipitation are very similar on average (differences of 0–14%), with good correlation between modelled and observed data (r2=0.50–0.78). Differences between the EMEP model and ICP measurements are thought to arise from a mixture of problems with both the observations and model. However, the overall conclusion is that the EMEP model performs rather well in reproducing patterns of S and N deposition to European forests.
Thermal stability responses of soil organic matter to long-term fertilization practices
Authors: Leifeld J. , Franko U. , Schulz E.
Published: April 2010

Abstract. We used differential scanning calorimetry (DSC) to infer thermal properties of soil organic matter (SOM) in the static fertilization experiment in Bad Lauchstädt, Germany, which has been established in 1902. Four treatments (null N, change from null to manuring in 1978 NM, change from manuring to null in 1978 MN, and permanent manure and mineral fertilization since 1902 M) were sampled in 2004. Soil organic carbon contents were highest for M (2.4%), lowest for N (1.7%), and similar for MN and NM (2.2%). Three heat flow peaks at around 354°C, 430°C, and 520°C, which were assigned to as thermally labile and stable SOM and combustion residues from lignite, respectively, characterized DSC thermograms. DSC peak temperatures were relatively constant among treatments, but peak heights normalized to the organic C content of the soil were significantly different for labile and stable SOM. Labile C was higher for M>MN=NM=N, and stable C decreased in the order N=NM>MN=M, showing that agricultural depletion of SOM increases the share of thermally stable C. Lignite-derived C was not affected by management, suggesting a homogeneous deposition across treatments.
Nitrous oxide in the North Atlantic Ocean
Authors: Walter S. , Bange H. W. , Breitenbach U. , Wallace D. W. R.
Published: April 2010

Abstract. In order to get a comprehensive picture of the distribution of nitrous oxide (N2O) in the North Atlantic Ocean, measurements of dissolved nitrous oxide were made during three cruises in the tropical, subtropical and cold-temperate North Atlantic Ocean in October/November 2002, March/April 2004, and May 2002, respectively. To account for the history of atmospheric N2O, we suggest a new depth-dependent calculation of excess N2O (ΔN2O). N2O depth profiles showed supersaturation throughout the water column with a distinct increasing trend from the cold-temperate to the tropical region. Lowest nitrous oxide concentrations, near equilibrium and with an average of 11.0±1.7 nmol L−1, were found in the cold-temperate North Atlantic where the profiles showed no clear maxima. Highest values up to 37.3 nmol L−1 occurred in the tropical North Atlantic with clear maxima at approximately 400 m. A positive correlation of nitrous oxide with nitrate, as well as excess nitrous oxide with the apparent oxygen utilization (AOU), was only observed in the subtropical and tropical regions. Therefore, we conclude that the formation of nitrous oxide via nitrification occurs in the tropical region rather than in the cold-temperate region of the North Atlantic Ocean
Source identification of nitrate by means of isotopic tracers in the Baltic Sea catchments
Authors: Voss M. , Deutsch B. , Elmgren R. , Humborg C. , Kuuppo P. , Pastuszak M. , Rolff C. , Schulte U.
Published: April 2010

Abstract. Nitrate input to a river is largely controlled by land use in its catchment. We compared the information carried by the isotopic signatures of nitrate in 12 Baltic rivers, in relation to the vegetation cover, land use, and fertilization of agricultural land of their catchments. We found isotope values in nitrate ranging from −2 to 14‰ for δ15N and 8 to 25‰ for δ18O. The annual variability of riverine nitrate isotope signatures is presented in detail for one Nordic, the Kemijoki, and two southern rivers, the Vistula and Oder. Nordic rivers with relatively pristine vegetation in their catchments show not only low δ15N values and high δ18O-NO3− but also lower annual variability than rivers draining densely populated land. Seasonal signals were found in all the rivers. We used load weighted nitrate isotope data and data from the three major N sources (farmland/sewage, atmospheric deposition and from runoff of pristine soils) to theoretically estimate the shares of nitrate from these sources. The results of an isotope mixing model (IMM-1) agree reasonably well with the same estimates for agricultural land derived from a Global Land Cover (GLC) data base, with a deviation varying from −16% to +26%. The comparison with an emission model (EM) reveals relatively good agreements for intensively used catchments (−18 to +18% deviation). Rather unsatisfactory agreement was found between the IMM-1 and GLC calculations for pristine catchments (−36 to +50% deviation). Advantages and limitations of the tested model are discussed.
Seasonal variation of mono- and sesquiterpene emission rates of Scots pine
Authors: Hakola H. , Tarvainen V. , Bäck J. , Ranta H. , Bonn B. , Rinne J. , Kulmala M.
Published: April 2010

Abstract. The seasonal variation of mono-and sesquiterpene emission rates of Scots pine was measured from April to October in 2004. The emission rates were measured daily in the afternoons with the exception of weekends. Emissions were measured from two branches; one of them was debudded in May (branch A), while the other was allowed to grow new needles (branch B). The monoterpene emission pattern remained almost constant throughout the measurement period, Δ3-carene being the dominant monoterpene (50-70% of the VOC emission). The standard monoterpene emission potential (30°C) was highest during early summer in June (the average of the two branches 1.35 µg g-1h-1) and lowest during early autumn in September (the average of the two branches 0.20 µg g-1h-1. The monoterpene emission potential of branch A remained low also during October, whereas the emission potential of branch B was very high in October. The sesquiterpenes were mainly emitted during mid summer, the dominant sesquiterpene being β-caryophyllene. Branch A had a higher sesquiterpene emission potential than branch B and the emission maximum occurred concomitant with the high concentration of airborne pathogen spores suggesting a potential defensive role of the sesquiterpene emissions. The sesquiterpene emissions were well correlated with linalool and 1,8-cineol emissions, but not with monoterpenes. Sesquiterpene and 1,8-cineol emissions were equally well described by the temperature dependent and the temperature and light dependent algorithms. This is due to the saturation of the light algorithm as the measurements were always conducted during high light conditions.
CO2 exchange and carbon balance in two grassland sites on eutrophic drained peat soils
Authors: Veenendaal E. M. , Kolle O. , Leffelaar P. A. , Schrier-Uijl A. P. , Van Huissteden J. , Van Walsem J. , Möller F. , Berendse F.
Published: April 2010

Abstract. In this study we investigated the role of intensive and extensive dairy farm practices on CO2 exchange and the carbon balance of peatlands by means of eddy covariance (EC) measurements. Year long EC measurements were made in two adjacent farm sites on peat soil in the western part of the Netherlands. One site (Stein) is a new meadow bird reserve and is managed predominantly by mowing in June and August. The second site (Oukoop) is an intensive dairy farm. Maximum photosynthetic uptake of the grass sward (range 2 to 34 μmol CO2 m−2 s−1) showed a close and similar linear relationship with Leaf Area Index (LAI; range 1 to 5) except in maturing hay meadows, where maximum photosynthetic uptake did not increase further. Apparent quantum yield varied between 0.02 and 0.08 (mean 0.045) μmol CO2 μmol−1 photons at both sites and was significantly correlated with LAI during the growth season. Ecosystem Respiration at 10°C (R10) calculated from the year round data set was 3.35 μmol CO2 m−2 s−1 at Stein and 3.69 μmol CO2 m−2 s−1 at Oukoop. Both sites were a source of carbon in winter and a sink during summer with net ecosystem exchange varying between 50 to 100 mmol CO2 m−2 d−1 in winter to below −400 mmol CO2 m−2 d−1 in summer. Periodically, both sites became a source after mowing. Net annual ecosystem exchange (NEE) for Stein was −5.7 g C m−2 a−1 and for Oukoop 133.9 g C m−2 a−1. When biomass removal, manure applications and estimates of methane emissions ware taken into account, both eutrophic peat meadows are a strong source for C around 420 g C m−2 a−1.
Microbiology and atmospheric processes: the role of biological particles in cloud physics
Authors: Möhler O. , DeMott P. J. , Vali G. , Levin Z.
Published: April 2010

Abstract. As part of a series of papers on the sources, distribution and potential impact of biological particles in the atmosphere, this paper introduces and summarizes the potential role of biological particles in atmospheric clouds. Biological particles like bacteria or pollen may be active as both cloud condensation nuclei (CCN) and heterogeneous ice nuclei (IN) and thereby can contribute to the initial cloud formation stages and the development of precipitation through giant CCN and IN processes. The paper gives an introduction to aerosol-cloud processes involving CCN and IN in general and provides a short summary of previous laboratory, field and modelling work which investigated the CCN and IN activity of bacterial cells and pollen. Recent measurements of atmospheric ice nuclei with a continuous flow diffusion chamber (CFDC) and of the heterogeneous ice nucleation efficiency of bacterial cells are also briefly discussed. As a main result of this overview paper we conclude that a proper assessment of the impact of biological particles on tropospheric clouds needs new laboratory, field and modelling work on the abundance of biological particles in the atmosphere and their CCN and heterogeneous IN properties.
Temperature response of soil respiration is dependent on concentration of readily decomposable C
Authors: Larionova A. A. , Yevdokimov I. V. , Bykhovets S. S.
Published: April 2010

Abstract. Temperature acclimation of soil organic matter (SOM) decomposition is one of the major uncertainties in predicting soil CO2 efflux associated with the increase in global mean temperature. A reasonable explanation for an apparent acclimation proposed by Davidson and colleagues (2006) based on Michaelis-Menten kinetics suggests that temperature sensitivity decreases when both maximal activity of respiratory enzymes (Vmax) and half-saturation constant (Ks) cancel each other upon temperature increase. We tested the hypothesis of the canceling effect by the mathematical simulation of data obtained in incubation experiments with forest and arable soils. Our data support the hypothesis and suggest that concentration of readily decomposable C substrate (as glucose equivalents) and temperature dependent substrate release are the important factors controlling temperature sensitivity of soil respiration. The highest temperature sensitivity of soil respiration was observed when substrate release was temperature dependent and C substrate concentration was much lower than Ks. Increase of substrate content to the half-saturation constant by glucose addition resulted in temperature acclimation associated with the canceling effect. Addition of the substrate to the level providing respiration at a maximal rate Vmax leads to the acclimation of the whole microbial community as such. However, growing microbial biomass was more sensitive to the temperature alterations. This study improves our understanding of the instability of temperature sensitivity of soil respiration under field conditions, attributing this phenomenon to changes in concentration of readily decomposable C substrate.
Environmental controls over methanol emission from leaves
Authors: Harley P. , Greenberg J. , Niinemets Ü. , Guenther A.
Published: April 2010

Abstract. Methanol is found throughout the troposphere, with average concentrations second only to methane among atmospheric hydrocarbons. Proposed global methanol budgets are highly uncertain, but all agree that at least 60% of the total source arises from the terrestrial biosphere and primary emissions from plants. However, the magnitude of these emissions is also highly uncertain, and the environmental factors which control them require further elucidation. Using a temperature-controlled leaf enclosure, we measured methanol emissions from leaves of six plant species by proton transfer reaction mass spectrometry, with simultaneous measurements of leaf evapotranspiration and stomatal conductance. Rates of emission at 30°C varied from 0.2 to 38 μg g (dry mass)−1 h−1, with higher rates measured on young leaves, consistent with the production of methanol via pectin demethylation in expanding foliage. On average, emissions increased by a factor of 2.3 for each 10°C increase in leaf temperature. At constant temperature, emissions were also correlated with co-varying incident photosynthetic photon flux density and rates of stomatal conductance. The data were analyzed using the emission model developed by Niinemets and Reichstein (2003a, b), with the incorporation of a methanol production term that increased exponentially with temperature. It was concluded that control of emissions, during daytime, was shared by leaf temperature and stomatal conductance, although rates of production may also vary diurnally in response to variations in leaf growth rate in expanding leaves. The model, which generally provided reasonable simulations of the measured data during the day, significantly overestimated emissions on two sets of measurements made through the night, suggesting that production rates of methanol were reduced at night, perhaps because leaf growth was reduced or possibly through a direct effect of light on production. Although the short-term dynamics of methanol emissions can be successfully modeled only if stomatal conductance and compound solubility are taken into account, emissions on longer time scales will be determined by rates of methanol production, controls over which remain to be investigated.
The unique skeleton of siliceous sponges (Porifera; Hexactinellida and Demospongiae) that evolved first from the Urmetazoa during the Proterozoic: a review
Authors: Müller W. E. G. ,   Jinhe Li, Schröder H. C. ,   Li Qiao,   Xiaohong Wang
Published: April 2010

Abstract. Sponges (phylum Porifera) had been considered as an enigmatic phylum, prior to the analysis of their genetic repertoire/tool kit. Already with the isolation of the first adhesion molecule, galectin, it became clear that the sequences of sponge cell surface receptors and of molecules forming the intracellular signal transduction pathways triggered by them, share high similarity with those identified in other metazoan phyla. These studies demonstrated that all metazoan phyla, including Porifera, originate from one common ancestor, the Urmetazoa. The sponges evolved prior to the Ediacaran-Cambrian boundary (542 million years ago [myr]) during two major "snowball earth events", the Sturtian glaciation (710 to 680 myr) and the Varanger-Marinoan ice ages (605 to 585 myr). During this period the ocean was richer in silica due to the silicate weathering. The oldest sponge fossils (Hexactinellida) have been described from Australia, China and Mongolia and are thought to have existed coeval with the diverse Ediacara fauna. Only little younger are the fossils discovered in the Sansha section in Hunan (Early Cambrian; China). It has been proposed that only the sponges possessed the genetic repertoire to cope with the adverse conditions, e.g. temperature-protection molecules or proteins protecting them against ultraviolet radiation. The skeletal elements of the Hexactinellida (model organisms Monorhaphis chuni and Monorhaphis intermedia or Hyalonema sieboldi) and Demospongiae (models Suberites domuncula and Geodia cydonium), the spicules, are formed enzymatically by the anabolic enzyme silicatein and the catabolic enzyme silicase. Both, the spicules of Hexactinellida and of Demospongiae, comprise a central axial canal and an axial filament which harbors the silicatein. After intracellular formation of the first lamella around the channel and the subsequent extracellular apposition of further lamellae the spicules are completed in a net formed of collagen fibers. The data summarized here substantiate that with the finding of silicatein a new aera in the field of bio/inorganic chemistry started. For the first time strategies could be formulated and experimentally proven that allow the formation/synthesis of inorganic structures by organic molecules. These findings are not only of importance for the further understanding of basic pathways in the body plan formation of sponges but also of eminent importance for applied/commercial processes in a sustainable use of biomolecules for novel bio/inorganic materials.
nirS-containing denitrifier communities in the water column and sediment of the Baltic Sea
Authors: Falk S. , Hannig M. , Gliesche C. , Wardenga R. , Köster M. , Jürgens K. , Braker G.
Published: April 2010

Abstract. The aim of this study was to compare structural differences in the nirS-type denitrifying microbial communities along the environmental gradients observed in the water column and coastal sediments of the Baltic Sea. To link community structure and environmental gradients, denitrifier communities were analyzed by terminal restriction fragment length polymorphism (T-RFLP) based on nirS as a functional marker gene for denitrification. nirS-type denitrifier community composition was further evaluated by phylogenetic analysis of nirS sequences from clone libraries. T-RFLP analysis indicated some overlap but also major differences between communities from the water column and the sediment. Shifts in community composition along the biogeochemical gradients were observed only in the water column while denitrifier communities were rather uniform within the upper 30 mm of the sediment. Specific terminal restriction fragments (T-RFs) indicative of the sulfidic zone suggest the presence of nitrate-reducing and sulfide-oxidizing microorganisms that were previously shown to be important at the suboxic-sulfidic interface in the water column of the Baltic Sea. Phylogenetic analysis of nirS genes from the Baltic Sea and of sequences from marine habitats all over the world indicated distinct denitrifier communities that grouped mostly according to their habitats. We suggest that these subgroups of denitrifiers had developed after selection through several factors, i.e. their habitats (water column or sediment), impact by prevalent environmental conditions and isolation by large geographic distances between habitats.
Effects of climate warming and declining species richness in grassland model ecosystems: acclimation of CO2 fluxes
Authors: Vicca S. , Serrano-Ortiz P. , De Boeck H. J. , Lemmens C. M. H. M. , Nijs I. , Ceulemans R. , Kowalski A. S. , Janssens I. A.
Published: April 2010

Abstract. To study the effects of warming and declining species richness on the carbon balance of grassland communities, model ecosystems containing one, three or nine species were exposed to ambient and elevated (ambient +3°C) air temperature. In this paper, we analyze measured ecosystem CO2 fluxes to test whether ecosystem photosynthesis and respiration had acclimated to warming after 28 months of continuous heating, and whether the degree of acclimation depended on species richness. In order to test whether acclimation occurred, short term temperature response curves were established for all communities in both treatments. At similar temperatures, lower flux rates in the heated communities as compared to the unheated communities would indicate thermal acclimation. Because plant cover was significantly higher in the heated treatment, we normalized the data for plant cover. Subsequently, down-regulation of both photosynthesis and respiration was observed. Although CO2 fluxes were larger in communities with higher species richness, species richness did not affect the degree of acclimation to warming. These results imply that models need to take thermal acclimation into account to simulate photosynthesis and respiration in a warmer world.
Long-term steady state 13C labelling to investigate soil carbon turnover in grasslands
Authors: Klumpp K. , Soussana J. F. , Falcimagne R.
Published: April 2010

Abstract. We have set up a facility allowing steady state 13CO2 labeling of short stature vegetation (12 m2) for several years. 13C labelling is obtained by scrubbing the CO2 from outdoors air with a self-regenerating molecular sieve and by replacing it with 13C depleted (−34.7±0.03‰) fossil-fuel derived CO2 The facility, which comprises 16 replicate mesocosms, allows to trace the fate of photosynthetic carbon in plant-soil systems in natural light and at outdoors temperature. This method was applied to the study of soil organic carbon turnover in temperate grasslands. We tested the hypothesis that a low disturbance by grazing and cutting of the grassland increases the mean residence time of carbon in coarse (>0.2 mm) soil organic fractions. Grassland monoliths (0.5×0.5×0.4 m) were sampled from high and low disturbance treatments in a long-term (14 yrs) grazing experiment and were placed during two years in the mesocosms. During daytime, the canopy enclosure in each mesocosm was supplied in an open flow with air at mean CO2 concentration of 425 µmol mol−1 and δ13C of −21.5±0.27‰. Fully labelled mature grass leaves reached a δ13C of −40.8 (±0.93) and −42.2‰ (±0.60) in the low and high disturbance treatments, respectively, indicating a mean 13C labelling intensity of 12.7‰ compared to unlabelled control grass leaves. After two years, the delta 13C value of total soil organic matter above 0.2 mm was reduced in average by 7.8‰ in the labelled monoliths compared to controls. The isotope mass balance technique was used to calculate for the top (0–10 cm) soil the fraction of 13C labelled carbon in the soil organic matter above 0.2 mm (i.e. roots, rhizomes and particulate organic matter). A first order exponential decay model fitted to the unlabelled C in this fraction shows an increase in mean residence time from 22 to 31 months at low compared to high disturbance. A slower decay of roots, rhizomes and particulate organic matter above 0.2 mm is therefore likely to contribute to the observed increased in soil carbon sequestration in grassland monoliths exposed to low disturbance.
The fate of pelagic CaCO3 production in a high CO2 ocean: a model study
Authors: Gehlen M. , Gangstø R. , Schneider B. , Bopp L. , Aumont O. , Ethe C.
Published: April 2010

Abstract. This model study addresses the change in pelagic calcium carbonate production (CaCO3, as calcite in the model) and dissolution in response to rising atmospheric CO2. The parameterization of CaCO3 production includes a dependency on the saturation state of seawater with respect to calcite. It was derived from laboratory and mesocosm studies on particulate organic and inorganic carbon production in Emiliania huxleyi as a function of pCO2. The model predicts values of CaCO3 production and dissolution in line with recent estimates. The effect of rising pCO2 on CaCO3 production and dissolution was quantified by means of model simulations forced with atmospheric CO2 increasing at a rate of 1% per year from 286 ppm to 1144 ppm over a 140 year time-period. The simulation predicts a decrease of CaCO3 production by 27%. The combined change in production and dissolution of CaCO3 yields an excess uptake of CO2 from the atmosphere by the ocean of 5.9 GtC over the period of 140 years.
Modulation of ecdysal cyst and toxin dynamics of two Alexandrium (Dinophyceae) species under small-scale turbulence
Authors: Bolli L. , Llaveria G. , Garcés E. , Guadayol Ò. , van Lenning K. , Peters F. , Berdalet E.
Published: April 2010

Abstract. Some dinoflagellate species have shown different physiological responses to certain turbulent conditions. Here we investigate how two levels of turbulent kinetic energy dissipation rates (ε = 0.4 and 27 cm² s−3) affect the PSP toxins and ecdysal cyst dynamics of two bloom forming species, Alexandrium minutum and A. catenella. The most striking responses were observed at the high ε generated by an orbital shaker. In the cultures of the two species shaken for more than 4 days, the cellular GTX(1+4) toxin contents were significantly lower than in the still control cultures. In A. minutum this trend was also observed in the C(1+2) toxin content. For the two species, inhibition of ecdysal cyst production occurred during the period of exposure of the cultures to stirring (4 or more days) at any time during their growth curve. Recovery of cyst abundances was always observed when turbulence stopped. When shaking persisted for more than 4 days, the net growth rate significantly decreased in A. minutum (from 0.25±0.01 day−1 to 0.19±0.02 day−1) and the final cell numbers were lower (ca. 55.4%) than in the still control cultures. In A. catenella, the net growth rate was not markedly modified by turbulence although under long exposure to shaking, the cultures entered earlier in the stationary phase and the final cell numbers were significantly lower (ca. 23%) than in the control flasks. The described responses were not observed in the experiments performed at the low turbulence intensities with an orbital grid system, where the population development was favoured. In those conditions, cells appeared to escape from the zone of the influence of the grids and concentrated in calmer thin layers either at the top or at the bottom of the containers. This ecophysiological study provides new evidences about the sensitivity to high levels of small-scale turbulence by two life cycle related processes, toxin production and encystment, in dinoflagellates. This can contribute to the understanding of the dynamics of those organisms in nature.
Carbon balance assessment of a natural steppe of southern Siberia by multiple constraint approach
Authors: Belelli Marchesini L. , Papale D. , Reichstein M. , Vuichard N. , Tchebakova N. , Valentini R.
Published: April 2010

Abstract. Steppe ecosystems represent an interesting case in which the assessment of carbon balance may be performed through a cross validation of the eddy covariance measurements against ecological inventory estimates of carbon exchanges (Ehman et al., 2002; Curtis et al., 2002). Indeed, the widespread presence of ideal conditions for the applicability of the eddy covariance technique, as vast and homogeneous grass vegetation cover over flat terrains (Baldocchi, 2003), make steppes a suitable ground to ensure a constrain to flux estimates with independent methodological approaches. We report about the analysis of the carbon cycle of a true steppe ecosystem in southern Siberia during the growing season of 2004 in the framework of the TCOS-Siberia project activities performed by continuous monitoring of CO2 fluxes at ecosystem scale by the eddy covariance method, fortnightly samplings of phytomass, and ingrowth cores extractions for NPP assessment, and weekly measurements of heterotrophic component of soil CO2 effluxes obtained by an experiment of root exclusion. The carbon balance of the monitored natural steppe was, according to micrometeorological measurements, a sink of carbon of 151.7±36.9 g C m−2, cumulated during the growing season from May to September. This result was in agreement with the independent estimate through ecological inventory which yielded a sink of 150.1 g C m−2 although this method was characterized by a large uncertainty (±130%) considering the 95% confidence interval of the estimate. Uncertainties in belowground process estimates account for a large part of the error. Thus, in particular efforts to better quantify the dynamics of root biomass (growth and turnover) have to be undertaken in order to reduce the uncertainties in the assessment of NPP. This assessment should be preferably based on the application of multiple methods, each one characterized by its own merits and flaws.
Model analysis of the effects of atmospheric drivers on storage water use in Scots pine
Authors: Verbeeck H. , Steppe K. , Nadezhdina N. , Op De Beeck M. , Deckmyn G. , Meiresonne L. , Lemeur R. , Čermák J. , Ceulemans R. , Janssens I. A.
Published: April 2010

Abstract. Storage water use is an indirect consequence of the interplay between different meteorological drivers through their effect on water flow and water potential in trees. We studied these microclimatic drivers of storage water use in Scots pine (Pinus sylvestris L.) growing in a temperate climate. The storage water use was modeled using the ANAFORE model, integrating a dynamic water flow and – storage model with a process-based transpiration model. The model was calibrated and validated with sap flow measurements for the growing season of 2000 (26 May–18 October). Because there was no severe soil drought during the study period, we were able to study atmospheric effects. Incoming radiation and vapour pressure deficit (VPD) were the main atmospheric drivers of storage water use. The general trends of sap flow and storage water use are similar, and follow more or less the pattern of incoming radiation. Nevertheless, considerable differences in the day-to-day pattern of sap flow and storage water use were observed. VPD was determined to be one of the main drivers of these differences. During dry atmospheric conditions (high VPD) storage water use was reduced. This reduction was higher than the reduction in measured sap flow. Our results suggest that the trees did not rely more on storage water during periods of atmospheric drought, without severe soil drought. The daily minimum tree water content was lower in periods of high VPD, but the reserves were not completely depleted after the first day of high VPD, due to refilling during the night. Nevertheless, the tree water content deficit was a third important factor influencing storage water use. When storage compartments were depleted beyond a threshold, storage water use was limited due to the low water potential in the storage compartments. The maximum relative contribution of storage water to daily transpiration was also constrained by an increasing tree water content deficit.
Iron profiles and speciation of the upper water column at the Bermuda Atlantic Time-series Study site: a model based sensitivity study
Authors: Weber L. , Völker C. , Oschlies A. , Burchard H.
Published: April 2010

Abstract. A one-dimensional model of the biogeochemistry and speciation of iron is coupled with the General Ocean Turbulence Model (GOTM) and a NPZD-type ecosystem model. The model is able to simulate the temporal patterns and vertical profiles of dissolved iron (dFe) in the upper ocean at the Bermuda Atlantic Time-series Study site reasonably well. Subsurface model profiles strongly depend on the parameter values chosen for the loss processes for iron, colloidal aggregation and scavenging onto particles. Estimates for these parameters based on observations in particle-rich waters result in depletion of dFe. A high stability constant of iron-binding organic ligands is required to reproduce the observed degree of organic complexation below the mixed layer. The scavenging residence time for iron in the model is shortest in spring and summer, because of the larger abundance of particles, and increases with depth towards values on the order of a hundred years. A solubility of atmospherically deposited iron higher than 2% lead to dFe concentrations incompatible with observations. Despite neglecting ultraviolet radiation, the model produces diurnal variations and mean vertical profiles of H2O2 and iron species that are in good agreement with observations.
Biogeochemical factors contributing to enhanced carbon storage following afforestation of a semi-arid shrubland
Authors: Grünzweig J. M. , Gelfand I. , Fried Y. , Yakir D.
Published: April 2010

Abstract. Ecosystems in dry regions are generally low in productivity and carbon (C) storage. We report, however, large increases in C sequestration following afforestation of a semi-arid shrubland with Pinus halepensis trees. Using C and nitrogen (N) inventories, based in part on site-specific allometric equations, we measured an increase in the standing ecosystem C stock from 2380 g C m−2 in the shrubland to 5840 g C m−2 in the forest after 35 years, with no significant change in N stocks. Carbon sequestration following afforestation was associated with increased N use efficiency as reflected by an overall increase in C/N ratio from 7.6 in the shrubland to 16.6 in the forest. The C accumulation rate in the forest was particularly high for soil organic C (SOC; increase of 1760 g C m−2 or 50 g C m−2 yr−1), which was associated with the following factors: 1) Analysis of a small 13C signal within this pure C3 system combined with size fractionation of soil organic matter indicated a significant addition of new SOC derived from forest vegetation (68% of total forest SOC) and a considerable portion of the old original shrubland SOC (53%) still remaining in the forest. 2) A large part of both new and old SOC appeared to be protected from decomposition as about 60% of SOC under both land-use types were in mineral-associated fractions. 3) A short-term decomposition study indicated decreased decomposition of lower-quality litter and SOC in the forest, based on reduced decay rates of up to 90% for forest compared to shrubland litter. 4) Forest soil included a significant component of live and dead roots (12% of total SOC). Our results suggest a role for increased N use efficiency, enhanced SOC protection and reduced decomposition rates in the large C sequestration potential following afforestation in semi-arid regions. These results are particularly relevant in light of persistent predictions of drying trends in the Mediterranean and other regions.
Natural variability of bio-optical properties in Case 1 waters: attenuation and reflectance within the visible and near-UV spectral domains, as observed in South Pacific and Mediterranean waters
Authors: Morel A. , Claustre H. , Antoine D. , Gentili B.
Published: April 2010

Abstract. The optical properties of Case 1 waters have been empirically related to the chlorophyll concentration, [Chl], historically used as an index of the trophic state and of the abundance of the biological materials. The well-known natural variability around the mean statistical relationships is here examined by comparing the apparent optical properties (spectral downward irradiance attenuation and reflectance) as a function of [Chl] in two Case 1 environments, the Pacific and Mediterranean waters. These oceanic zones apparently represent two extremes of the possible bio-optical variability range around the mean. The systematic deviations, in both directions with respect to the average laws, mainly result from the differing contents in non-algal detrital materials and dissolved colored substance for a given [Chl] level. These contents are higher than the average in the Mediterranean Sea, and lower in the Pacific Ocean, respectively. These divergences between the two water bodies, detectable in the visible spectral domain, are considerably accentuated in the UV domain. The bio-optical properties in this spectral domain (310–400 nm) are systematically explored. They are more varying for a given [Chl] than those in the visible domain. Their prediction based on the sole [Chl] index is thus problematic, although it is probably possible on a regional scale if reliable field data are available. It does not seem, however, that ubiquitous relationships exist for this spectral domain for all Case 1 waters at global scale.
Methodical study of nitrous oxide eddy covariance measurements using quantum cascade laser spectrometery over a Swiss forest
Authors: Eugster W. , Zeyer K. , Zeeman M. , Michna P. , Zingg A. , Buchmann N. , Emmenegger L.
Published: April 2010

Abstract. Nitrous oxide fluxes were measured at the Lägeren CarboEurope IP flux site over the multi-species mixed forest dominated by European beech and Norway spruce. Measurements were carried out during a four-week period in October–November 2005 during leaf senescence. Fluxes were measured with a standard ultrasonic anemometer in combination with a quantum cascade laser absorption spectrometer that measured N2O, CO2, and H2O mixing ratios simultaneously at 5 Hz time resolution. To distinguish insignificant fluxes from significant ones it is proposed to use a new approach based on the significance of the correlation coefficient between vertical wind speed and mixing ratio fluctuations. This procedure eliminated roughly 56% of our half-hourly fluxes. Based on the remaining, quality checked N2O fluxes we quantified the mean efflux at 0.8±0.4 μmol m−2 h−1 (mean ± standard error). Most of the contribution to the N2O flux occurred during a 6.5-h period starting 4.5 h before each precipitation event. No relation with precipitation amount could be found. Visibility data representing fog density and duration at the site indicate that wetting of the canopy may have as strong an effect on N2O effluxes as does below-ground microbial activity. It is speculated that above-ground N2O production from the senescing leaves at high moisture (fog, drizzle, onset of precipitation event) may be responsible for part of the measured flux.
Growth and specific P-uptake rates of bacterial and phytoplanktonic communities in the Southeast Pacific (BIOSOPE cruise)
Authors: Duhamel S. , Moutin T. , Van Wambeke F. , Van Mooy B. , Rimmelin P. , Raimbault P. , Claustre H.
Published: April 2010

Abstract. Predicting heterotrophic bacteria and phytoplankton specific growth rates (μ ) is of great scientific interest. Many methods have been developed in order to assess bacterial or phytoplankton μ. One widely used method is to estimate μ from data obtained on biomass or cell abundance and rates of biomass or cell production. According to Kirchman (2002), the most appropriate approach for estimating μ is simply to divide the production rate by the biomass or cell abundance estimate. Most methods using this approach to estimate μ are based on carbon (C) incorporation rates and C biomass measurements. Nevertheless it is also possible to estimate μ using phosphate (P) data. We showed that particulate phosphate (PartP) can be used to estimate biomass and that the P uptake rate to PartP ratio can be employed to assess μ. Contrary to other methods using C, this estimator does not need conversion factors and provides an evaluation of μ for both autotrophic and heterotrophic organisms. We report values of P-based μ in three size fractions (0.2–0.6; 0.6–2 and >2 μm) along a Southeast Pacific transect, over a wide range of P-replete trophic status. P-based μ values were higher in the 0.6–2 μm fraction than in the >2 μm fraction, suggesting that picoplankton-sized cells grew faster than the larger cells, whatever the trophic regime encountered. Picoplankton-sized cells grew significantly faster in the deep chlorophyll maximum layer than in the upper part of the photic zone in the oligotrophic gyre area, suggesting that picoplankton might outcompete >2 μm cells in this particular high-nutrient, low-light environment. P-based μ attributed to free-living bacteria (0.2-0.6 μm) and picoplankton (0.6–2 μm) size-fractions were relatively low (0.11±0.07 d−1 and 0.14±0.04 d−1, respectively) in the Southeast Pacific gyre, suggesting that the microbial community turns over very slowly.
Early diagenetic overprint in Caribbean sediment cores and its effect on the geochemical composition of planktonic foraminifera
Authors: Regenberg M. , Nürnberg D. , Schönfeld J. , Reichart G.-J.
Published: April 2010

Abstract. Early diagenetic features are noticed in the vicinity of carbonate platforms. Planktonic foraminifera of two tropical Atlantic deep-sea sediment cores show the strict relation between micro-scale euhydral crystallites of inorganic precipitates, higher oxygen isotope values and Mg/Ca ratios, and lower Sr/Ca ratios than expected for their pelagic environment in the time interval of ~100 000–550 000 calendar years before present. Laser ablation Mg/Ca (Sr/Ca) of crystallite-bearing foraminiferal chamber walls revealed 4–6 times elevated (2–3 times depleted) ratios, when ablating the diagenetic overgrowth. Crystalline overgrowth in proportion of 10–20% are estimated to cause the observed geochemical alteration. The extent of foraminiferal Mg/Ca alteration, moreover, seems to be controlled by the composition of the bulk sediment, especially the content of high-magnesium calcite. Anomalous ratios of >6 mmol/mol only occur, when high-magnesium calcite has dissolved within the sediment. The older parts (back to ~800 kyrs) of the records are characterized by similar trends of Mg/Ca and Sr/Ca. We discuss possible scenarios to accommodate the obtained geochemical information.