A multi-proxy Late-glacial palaeoenvironmental record from Lake Bled, Slovenia

This study investigates the palaeoecological record (δ¹⁸O, δ¹³C, pollen, plant macrofossils, chironomids and cladocera) at Lake Bled (Slovenia) sedimentary core to better understand the response of terrestrial and aquatic ecosystems to Late-glacial climatic fluctuations. The multi-proxy record suggests that in the Oldest Dryas, the landscape around Lake Bled was rather open, presumably because of the cold and dry climate, with a trend towards wetter conditions, as suggested by an increase in tree pollen as well as chironomid and cladocera faunas typical for well-oxygenated water. Climatic warming at the beginning of the Late-glacial Interstadial at ca. 14,800 cal yr BP is suggested by an increase in the δ¹⁸O value, the appearance of Betula and Larix pollen and macrofossils, and a warmth-adapted chironomid fauna. With further warming at ca. 13,800 cal yr BP, broad-leaved tree taxa (Quercus, Tilia, Ulmus), Artemisia, and Picea increase, whereas chironomid data (Cricotopus B) suggest lowering of lake levels. After 12,800 cal yr BP (and throughout the Younger Dryas), the climate was colder and drier, as indicated by lower δ¹⁸O values, decline of trees, increase of microscopic charcoal, xerophytes and littoral chironomids. A warmer climate, together with the spread of broad-leaved tree taxa and a deeper, more productive lake, mark the onset of the Late-glacial/Holocene transition. These results suggest that terrestrial and aquatic ecosystems at Lake Bled were very dynamic and sensitive to Late-glacial climatic fluctuations. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorised users. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water     

The diet of <Emphasis Type="Italic">Metaschizotherium bavaricum</Emphasis> (Chalicotheriidae,Mammalia) from the MN 5 of Sandelzhausen (Germany) implied by the mesowear method

The genus Metaschizotherium is a Miocene member of the Schizotheriinae (Chalicotheriidae, Perissodactyla) and appears in the MN 5 of Southern Germany with the species M. bavaricum. The Chalicotheriidae have mostly been reconstructed as browsers. In this study, the mesowear method is applied to 11 upper premolars and molars of M. bavaricum from the Upper Freshwater Molasse locality of Sandelzhausen (MN 5). With this method the amount of abrasive and attritive dental wear is investigated and thus it provides a time-averaged signature of food abrasiveness of ungulates. Principal components analysis is performed on mesowear variables of M. bavaricum. This species is found to classify closest to extant mixed feeding ruminants. This indicates that the diet of M. bavaricum essentially included nonabrasive browse but also a certain amount of abrasive plant material. The composition of the diet of extant reference species indicates that this abrasiveness was most likely imposed by bark and whole branches. In the palaeoecological context of Sandelzhausen M. bavaricum occupied the dietary niche of a mixed feeder or an abrasion-dominated browser. A high degree of similarity is recognised between the mesowear patterns of M. bavaricum from Sandelzhausen and M. fraasi from the MN 6 of the Franconian Alb. This is interpreted as reflecting a similar dietary niche of the two species.      

Determinants of isotopic coupling of CO2 and water vapour within a Quercus petraea forest canopy

Concentration and isotopic composition (δ¹³C and δ¹⁸O) of ambient CO₂ and water vapour were determined within a Quercus petraea canopy, Northumberland, UK. From continuous measurements made across a 36-h period from three heights within the forest canopy, we generated mixing lines (Keeling plots) for δ_a ¹³CO₂, δ_a C¹⁸O¹⁶O and δ_a H₂ ¹⁸O, to derive the isotopic composition of the signal being released from forest to atmosphere. These were compared directly with measurements of different respective pools within the forest system, i.e. δ¹³C of organic matter input for δ_a ¹³CO₂, δ¹⁸O of exchangeable water for δ_a C¹⁸O¹⁶O and transpired water vapour for δ_a H₂ ¹⁸O. [CO₂] and δ_a ¹³CO₂ showed strong coupling, where the released CO₂ was, on average, 4 per mil enriched compared to the organic matter of plant material in the system, suggesting either fractionation of organic material before eventual release as soil-respired CO₂, or temporal differences in ecosystem discrimination. δ_a C¹⁸O¹⁶O was less well coupled to [CO₂], probably due to the heterogeneity and transient nature of water pools (soil, leaf and moss) within the forest. Similarly, δ_a H₂ ¹⁸O was less coupled to [H₂O], again reflecting the transient nature of water transpired to the forest, seen as uncoupling during times of large changes in vapour pressure deficit. The δ¹⁸O of transpired water vapour, inferred from both mixing lines at the canopy scale and direct measurement at the leaf level, approximated that of source water, confirming that an isotopic steady state held for the forest integrated over the daily cycle. This demonstrates that isotopic coupling of CO₂ and water vapour within a forest canopy will depend on absolute differences in the isotopic composition of the respective pools involved in exchange and on the stability of each of these pools with time. Received: 21 March 1998 / Accepted: 10 December 1998     

Ectothermic vertebrates (Actinopterygii,Allocaudata, Urodela,Anura, Crocodylia,Squamata) from the Miocene of Sandelzhausen (Germany,Bavaria) and their implications for environment reconstruction and palaeoclimate

The Early to Middle Miocene fossil locality Sandelzhausen has yielded 48 species of ectothermic vertebrates and thus represents one of the most diverse ectotherm faunas of Miocene age. Thirty-five taxa of fishes, amphibians and reptiles, including three new species: Pelobates fahlbuschi nov. sp. (Pelobatidae, the most abundant vertebrate), Tropidophorus bavaricus nov. sp. (Lygosominae) and Bavaricordylus molassicus nov. sp. (Cordylidae), are described. Three additional species are new, but are not named yet: Ranidae indet. nov. gen. et sp., Anguidae gen. indet. sp. nov. and Palaeoblanus sp. nov. (Amphisbaenidae). In order to reconstruct the palaeoenvironment and past hydrologic conditions, a new methodology (the tooth replacement method, TRM) is introduced, which allows for the detection of autochthonous components within freshwater fish taphocoenose. TRM is tested on 45 localities from the Upper Freshwater Molasse and gives reasonable results in agreement with other analytical approaches. It is therefore viewed as a reliable method to distinguish perennial from seasonal water conditions at the Sandelzhausen locality. Using the TRM it was demonstrated that the palaeohydrology of Sandelzhausen is characterized by a change from temporary water to permanent water conditions. During the period of temporary water conditions (units B to D1, lower part) the ecosystem was driven by seasonal inundations, and the remaining riparian pools have yielded no autochthonous fish population, but acted as spawning places for amphibians (amphibian pool). A mostly open habitat in the close vicinity, with sandy and non-groundwater-affected soils during the dry season, is suggested based on the absolute dominance of the spadefoot Pelobates fahlbuschi nov. sp. This ecosystem changed up-section (late part of unit D1 and during D2 and E) due to the establishment of permanent water conditions of riparian pond type, preserving an autochthonous Palaeocarassius/Channa fish population (fish pond). The reconstructed precipitation values suggest that the observed change in hydrologic conditions was probably driven by climate. The lower part of the section gives semi-arid/sub-humid values, with 571 mm mean annual precipitation (MAP), whereas the upper part yields sub-humid/humid values of 847 mm MAP. The increase in precipitation by about 280 mm was perhaps caused by a less seasonal precipitation regime with concomitant higher regional groundwater tables during units D2 and E. Based on the occurrence of several thermophilous reptile species, and in agreement with palaeobotanical and oxygen isotope data, the climate of Sandelzhausen is interpreted as subtropical with mean annual temperatures from 18°C to 20.8°C, mean cold month temperatures from 12.6°C to 13.3°C and mean warm month temperatures from 25.1°C to 28.1°C.     

Isotopic signature of nitrate in two contrasting watersheds of Brush Brook,Vermont, USA

We used the dual isotope method to study differences in nitrate export in two subwatersheds in Vermont, USA. Precipitation, soil water and streamwater samples were collected from two watersheds in Camels Hump State Forest, located within the Green Mountains of Vermont. These samples were analyzed for the δ¹⁵N and δ¹⁸O of NO₃⁻. The range of δ¹⁵N–NO₃⁻ values overlapped, with precipitation −4.5‰ to +2.0‰ (n = 14), soil solution −10.3‰ to +6.2‰ (n = 12) and streamwater +0.3‰ to +3.1‰ (n = 69). The δ¹⁸O of precipitation NO₃⁻ (mean 46.8 ± 11.5‰) was significantly different (P < 0.001) from that of the stream (mean 13.2 ± 4.3‰) and soil waters (mean 14.5 ± 4.2‰) even during snowmelt periods. Extracted soil solution and streamwater δ¹⁸O of NO₃⁻ were similar and within the established range of microbially produced NO₃⁻, demonstrating that NO₃⁻ was formed by microbial processes. The δ¹⁵N and δ¹⁸O of NO₃⁻ suggests that although the two tributaries have different seasonal NO₃⁻ concentrations, they have a similar NO₃⁻ source.     

Changes in partial pressures of respiratory gases during submerged voluntary breath hold across odontocetes: is body mass important?

Odontocetes have an exceptional range in body mass spanning 10³ kg across species. Because, size influences oxygen utilization and carbon dioxide production rates in mammals, this lineage likely displays an extraordinary variation in oxygen store management compared to other marine mammal groups. To examine this, we measured changes in the partial pressures of respiratory gases ( P_\textO2 P_{{{\text{O}}_{2} }} , P_\textCO2 P_{{{\text{CO}}_{2} }} ), pH, and lactate in the blood during voluntary, quiescent, submerged breath holds in Pacific white-sided dolphins (Lagenorhynchus obliquidens), bottlenose dolphins (Tursiops truncatus), and a killer whale (Orcinus orca) representing a mass range of 96–3,850 kg. These measurements provided an empirical determination of the effect of body size on the variability in blood biochemistry during breath hold and experimentally determined aerobic dive limits (ADL) within one taxonomic group (odontocetes). For the species in this study, maximum voluntary breath-hold duration was positively correlated with body mass, ranging from 3.5 min in white-sided dolphins to 13.3 min for the killer whale. Variation in breath-hold duration was associated with differences in the rate of change for P_\textO2 P_{{{\text{O}}_{2} }} throughout breath hold; P_\textO2 P_{{{\text{O}}_{2} }} decreased twice as fast for the two smaller species (−0.6 mmHg O₂ min⁻¹) compared to the largest species (−0.3 mmHg O₂ min⁻¹). In contrast, the rate of increase in P_\textCO2 P_{{{\text{CO}}_{2} }} during breath hold was similar across species. These results demonstrate that large body size in odontocetes facilitates increased aerobic breath-hold capacity as mediated by decreased mass-specific metabolic rates (rates of change in P_\textO2 P_{{{\text{O}}_{2} }} served as a proxy for oxygen utilization). Indeed the experimentally determined 5 min ADL for bottlenose dolphins was surpassed by the 13.3 min maximum breath hold of the killer whale, which did not end in a rise in lactate. Rather, breath hold ended voluntarily as respiratory gases and pH fell within a narrow range for both large and small species, likely providing cues for ventilation.     

Insect cells respiratory activity in bioreactor

Specific respiration rate ( ) is a key parameter to understand cell metabolism and physiological state, providing useful information for process supervision and control. In this work, we cultivated different insect cells in a very controlled environment, being able to measure . Spodoptera frugiperda (Sf9) cells have been used through virus infection as host for foreign protein expression and bioinsecticide production. Transfected Drosophila melanogaster (S2) cells can be used to produce different proteins. The objective of this work is to investigate respiratory activity and oxygen transfer during the growth of different insect cells lines as Spodoptera frugiperda (Sf9), Drosophila melanogaster (S2) wild and transfected for the expression of GPV and EGFP. All experiments were performed in a well-controlled 1-L bioreactor, with SF900II serum free medium. Spodoptera frugiperda (Sf9) cells reached 10.7 × 10⁶ cells/mL and maximum specific respiration rate () of 7.3 × 10⁻¹⁷ molO₂/cell s. Drosophila melanogaster (S2) cells achieved 51.2 × 10⁶ cells/mL and of 3.1 × 10^–18 molO₂/cell s. S2AcGPV (expressing with rabies virus glycoprotein) reached 24.9 × 10⁶ cells/mL and of 1.7 × 10^–17 molO₂/cell s, while S2MtEGFP (expressing green fluorescent protein) achieved 15.5 × 10⁶ cells/mL and  = 1.9 × 10⁻¹⁷ molO₂/cell s. Relating to the Sf9, S2 cells reached higher maximum cell concentrations and lower specific respiration rate, which can be explained by its smaller size. These results presented useful information for scale-up and process control of insect cells.     

Bat breath reveals metabolic substrate use in free-ranging vampires

We analysed the stable carbon isotope ratio in exhaled CO₂ (δ¹³C_breath) of free-ranging vampires to assess the type of metabolized substrate (endogenous or exogenous substrate) and its origin, i.e. whether the carbon atoms came from a C₄ food web (grass and cattle) or the C₃ food web in which they were captured (a rainforest remnant and its mammals). For an improved understanding of factors influencing the δ¹³C_breath of vampires, we conducted feeding experiments with captive animals. The mean δ¹³C_breath of starved bats was depleted in ¹³C in relation to the diet by 4.6‰ (n = 10). Once fed with blood, δ¹³C_breath levelled off within a short time approximately 2.2‰ above the stable carbon isotope signature of the diet. The median time required to exchange 50% of the carbon atoms in exhaled CO₂ with carbon atoms from the ingested blood was 18.6 min (mean 29.5 ± 19.0 min, n = 5). The average δ¹³C of wing membrane and fur in free-ranging vampire bats suggested that bats almost exclusively foraged for cattle blood during the past weeks. The δ¹³C_breath of the same bats averaged −19.1‰. Given that all free-ranging vampires were starving and that the δ¹³C of cattle was more in enriched in ¹³C by 5–6‰ than the δ¹³C_breath of vampires, we conclude that the vampire bats of our study metabolised fat that was predominantly built from carbon atoms originating from cattle blood. Since δ¹³C of wing membrane and fur integrates over weeks and months respectively and δ¹³C_breath over hours and days, we also conclude that vampire bats of the studied population consistently ignored rainforest mammals and chose cattle as their prey during and prior to our study.     

Evaporation effects as reflected in freshwaters and ostracod calcite from modern environments in Central and Northeast Yakutia (East Siberia,Russia)

Taxonomical and geochemical investigations on freshwater ostracods from 15 waters in Central and Northeast (NE) Yakutia have been undertaken in order to estimate their potential usefulness in palaeoenvironmental reconstructions based on regional fossil records. Higher variability in environmental factors such as pH, electrical conductivity, and ionic content was observed in thermokarst-affected lakes in Central Yakutia than in NE Yakutia lakes. Species diversity of freshwater ostracods reached up to eight taxa per lake, mostly dominated by Candona weltneri Hartwig 1899, in Central Yakutia, whereas in NE Yakutian waters the diversity was lower and Candona muelleri jakutica Pietrzeniuk 1977 or Fabaeformiscandona inaequivalvis (Sars 1898) had highest frequencies. Coupled analyses of stable isotopes (δ¹⁸O, δ¹³C) and element ratios (Sr/Ca, Mg/Ca) were performed on both host waters and ostracod calcite, aiming to estimate the modern relationships. Correlations between host waters and ostracod calcite of single species were found for δ¹⁸O, δ¹³C and Sr/Ca and Mg/Ca ratios. The relationships between δ¹⁸O, Mg/Ca and Sr/Ca ratios and electrical conductivity (salinity) as an expression of solute concentrations in the waters mainly controlled by evaporation are more complicated but evident, and may be useful in future interpretation of geochemical data from fossil Siberian ostracods. Handling editor: K. Martens     

Isotope Systematics of Sulfate-oxygen and Sulfate-sulfur in Six European Peatlands

Oxygen (O) and sulfur (S) isotope systematics in bog water sulfates were determined for six Sphagnum dominated wetlands located in the British Isles and the Czech Republic, Central Europe. Comparison of a polluted and unpolluted site showed that 4 times higher atmospheric S inputs led to 3 times higher bog water sulfate concentrations and substrate S concentrations, 3 times increased ranges of substrate S concentrations, and 3 times increased ranges of δ³⁴S values. Sites with elevated atmospheric S inputs exhibited greater geochemical variability in wetland S species. Sulfate O–S isotope composition of bog pore water at a depth of 40 cm below surface differed from that of surface bog water, indicating that dissimilatory bacterial sulfate reduction, a process known to discriminate against the heavier isotopes ¹⁸O and ³⁴S, occurred in surface peat layers. While bacterial sulfate reduction remained to be one of the main isotope-selective processes for sulfate in peat, it could not fully explain the O–S isotope systematics of peat waters. The ‘residual’ sulfate was not simultaneously enriched in the heavier isotopes ¹⁸O and ³⁴S. Mixing of residual sulfate following bacterial sulfate reduction with the product of S²⁻ reoxidation, cleavage of esters, and isotope exchange reactions may have contributed to the decoupling of the δ³⁴S_so4 and δ¹⁸S_so4 values. Large within-site differences in δ¹⁸S_so4 and δ³⁴S_so4 (up to 13 and 15‰, respectively) indicated little communication between the 0 and 40 cm peat depth at some sites. Extremely high δ¹⁸S_so4 and δ³⁴S_so4 values found in several peat bog water samples from Connemara (Ireland), Thorne Moors (England) and Ocean (Czech Republic) were not seen in streams draining the wetlands. Direct runoff of atmogenic sulfate constituted a significant portion of the bog outflow. At the wetland scale, zones of dissimilatory bacterial sulfate reduction form pockets whose lateral hydrological fluxes are small.     

Using the water signal to detect invisible exchanging protons in the catalytic triad of a serine protease

Chemical Exchange Saturation Transfer (CEST) is an MRI approach that can indirectly detect exchange broadened protons that are invisible in traditional NMR spectra. We modified the CEST pulse sequence for use on high-resolution spectrometers and developed a quantitative approach for measuring exchange rates based upon CEST spectra. This new methodology was applied to the rapidly exchanging Hδ1 and Hε2 protons of His57 in the catalytic triad of bovine chymotrypsinogen-A (bCT-A). CEST enabled observation of Hε2 at neutral pH values, and also allowed measurement of solvent exchange rates for His57-Hδ1 and His57-Hε2 across a wide pH range (3–10). Hδ1 exchange was only dependent upon the charge state of the His57 (k _ex,Im+ = 470 s⁻¹, k _ex,Im = 50 s⁻¹), while Hε2 exchange was found to be catalyzed by hydroxide ion and phosphate base ( k_{\textOH ^-} k_{{{\text{OH}}^{ - } }}  = 1.7 × 10¹⁰ M⁻¹ s⁻¹, k_{\textHPO4^{2 -}} k_{{{\text{HPO}}_{4}^{2 - } }}  = 1.7 × 10⁶ M⁻¹ s⁻¹), reflecting its greater exposure to solute catalysts. Concomitant with the disappearance of the Hε2 signal as the pH was increased above its pK _a, was the appearance of a novel signal (δ = 12 ppm), which we assigned to Hγ of the nearby Ser195 nucleophile, that is hydrogen bonded to Nε2 of neutral His57. The chemical shift of Hγ is about 7 ppm downfield from a typical hydroxyl proton, suggesting a highly polarized O–Hγ bond. The significant alkoxide character of Oγ indicates that Ser195 is preactivated for nucleophilic attack before substrate binding. CEST should be generally useful for mechanistic investigations of many enzymes with labile protons involved in active site chemistry.     

The effect of temperature on post-feeding ammonia excretion and oxygen consumption in the southern catfish

The post-prandial rates of ammonia excretion (TAN) and oxygen consumption in the southern catfish (Silurus meridionalis) were assessed at 2 h intervals post-feeding until the rates returned to those of the fasting rates, at 17.5, 22.5, 27.5, and 32.5°C, respectively. Both fasting TAN and increased with temperature, and were lower than those previously reported for many fish species. The relationship between fasting TAN (mmol NH₃–N kg⁻¹ h⁻¹) and temperature (T, °C) was described as: fasting TAN = 0.144e ^0.0266T (r = 0.526, n = 27, P < 0.05). The magnitude of ammonia excretion and its ratio to total N intake during the specific dynamic action (SDA) tended to increase initially, and then decrease with increasing temperature. The ammonia quotient (AQ), calculated as mol NH₃–N/mol O₂, following feeding decreased as temperature increased. The relationship between AQ during SDA and temperature was described as: AQ_{during SDA} = 0.303e ^−0.0143T (r = 0.739, n = 21, P < 0.05). Our results suggest that ammonia excretion and oxygen consumption post-feeding are operating independently of each other. Furthermore, it appears that the importance of protein as a metabolic substrate in postprandial fish decreases with temperature.     

Phenol biodegradation by the thermoacidophilic archaeon <Emphasis Type="Italic">Sulfolobus solfataricus</Emphasis> 98/2 in a fed-batch bioreactor

Toxic at low concentrations, phenol is one of the most common organic pollutants in air and water. In this work, phenol biodegradation was studied in extreme conditions (80°C, pH = 3.2) in a 2.7 l bioreactor with the thermoacidophilic archaeon Sulfolobus solfataricus 98/2. The strain was first acclimatized to phenol on a mixture of glucose (2000 mg l⁻¹) and phenol (94 mg l⁻¹) at a constant dissolved oxygen concentration of 1.5 mg l⁻¹. After a short lag-phase, only glucose was consumed. Phenol degradation then began while glucose was still present in the reactor. When glucose was exhausted, phenol was used for respiration and then for biomass build-up. After several batch runs (phenol < 365 mg l⁻¹), specific growth rate (μ_X) was 0.034 ± 0.001 h⁻¹, specific phenol degradation rate (q_P) was 57.5 ± 2 mg g⁻¹ h⁻¹, biomass yield (Y_X/P) was 52.2 ± 1.1 g mol⁻¹, and oxygen yield factor ( \textY_{\textX/\textO 2} ) \left( {{\text{Y}}_{{{\text{X}}/{\text{O}}_{ 2} }} } \right) was 9.2 ± 0.2 g mol⁻¹. A carbon recovery close to 100% suggested that phenol was exclusively transformed into biomass (35%) and CO₂ (65%). Molar phenol oxidation constant ( \textY_{\textO 2 /\textP} ) \left( {{\text{Y}}_{{{\text{O}}_{ 2} /{\text{P}}}} } \right) was calculated from stoichiometry of phenol oxidation and introducing experimental biomass and CO₂ conversion yields on phenol, leading to values varying between 4.78 and 5.22 mol mol⁻¹. Respiratory quotient was about 0.84 mol mol⁻¹, very close to theoretical value (0.87 mol mol⁻¹). Carbon dioxide production, oxygen demand and redox potential, monitored on-line, were good indicators of growth, substrate consumption and exhaustion, and can therefore be usefully employed for industrial phenol bioremediation in extreme environments.     

A molecular dynamics study on opioid activities of biphalin molecule

Molecular dynamics simulations of the biphalin molecule, (Tyr-D-Ala-Gly-Phe-NH)₂, and the active tetrapeptide hydrazide, Tyr-D-Ala-Gly-Phe-NH-NH₂ were performed to investigate the cause of the increased μ and δ receptor binding affinities of the former over the latter. The simulation results demonstrate that the acylation of the two equal tetrapeptide fragments of biphalin produces the constrained hydrazide bridges C₄^a - C₄￠- N₉ - N₁₀ {\hbox{C}}_4^{\alpha } - {{\hbox{C}}_4}\prime - {{\hbox{N}}_9} - {{\hbox{N}}_{{10}}} and N₉ - N₁₀ - C₅￠- C₅^a {{\hbox{N}}_9} - {{\hbox{N}}_{{10}}} - {{\hbox{C}}_5}\prime - {\hbox{C}}_5^{\alpha } , which in turn increase the opportunity of conformations for binding to μ or δ receptors. Meanwhile, the connection of the two active tetrapeptide fragments of biphalin also results in the constrained side chain torsion angle χ² at one of the two residues Phe. This constrained side chain torsion angle not only significantly increases the δ receptor binding affinity but also makes most of the δ receptor binding conformations of biphalin bind to the δ receptor through the fragment containing the mentioned residue Phe.     

Differential water resource use by herbaceous and woody plant life-forms in a shortgrass steppe community

We conducted a study to test the predictions of Walter's two-layer model in the shortgrass steppe of northeastern Colorado. The model suggests that grasses and woody plants use water resources from different layers of the soil profile. Four plant removal treatments were applied in the spring of 1996 within a plant community codominated by Atriplex canescens (a C₄ shrub) and Bouteloua gracilis (a C₄ grass). During the subsequent growing season, soil water content was monitored to a depth of 180 cm. In addition, stem and leaf tissue of Atriplex, Bouteloua and the streamside tree Populus sargentii were collected monthly during the growing seasons of 1995 and 1996 for analysis of the δ¹⁸O value of plant stem water (for comparison with potential water sources) and the δ¹³C value of leaves (as an indicator of plant water status). Selective removal of shrubs did not significantly increase water storage at any depth in the measured soil profile. Selective removal of the herbaceous understory (mainly grasses) increased water storage in the top 60 cm of the soil. Some of this water gradually percolated to lower layers, where it was utilized by the shrubs. Based on stem water δ¹⁸O values, grasses were exclusively using spring and summer rain extracted from the uppermost soil layers. In contrast, trees were exclusively using groundwater, and the consistent δ¹³C values of tree leaves over the course of the summer indicated no seasonal changes in gas exchange and therefore minimal water stress in this life-form. Based on anecdotal rooting-depth information and initial measurements of stem water δ¹⁸O, shrubs may have also had access to groundwater. However, their overall δ¹⁸O values indicated that they mainly used water from spring and summer precipitation events, extracted from subsurface soil layers. These findings indicate that the diversity of life-forms found in this shortgrass steppe community may be a function of the spatial partitioning of soil water resources, and their differential use by grasses, shrubs, and trees. Consequently, our findings support the two-layer model in a broad sense, but indicate a relatively flexible strategy of water acquisition by shrubs. Received: 23 December 1997 / Accepted: 16 September 1998     

Enrichment of oxygen heavy isotopes during photosynthesis in phytoplankton

Some of the oxygen produced during oxygenic photosynthesis is consumed but little is known about the extent of the processes involved. We measured the ¹⁷O/¹⁶O and ¹⁸O/¹⁶O ratios in O₂ produced by certain marine and freshwater phytoplankton representing important groups of primary producers. When the cells were performing photosynthesis under very low dissolved oxygen concentrations (<3 μM), we observed significant enrichment in both ¹⁸O and ¹⁷O with respect to the substrate water. The difference in δ¹⁸O between O₂ and water was about 4.5, 3, 5.5, and 7‰ in the diatom Phaeodactylum tricornutum, Nannochloropsis sp. (Eustigmatophyceae), the coccolithophore Emiliania huxleyi and the green alga Chlamydomonas reinhardtii, respectively. The difference in δ¹⁷O was about 0.52 that of δ¹⁸O. As explained, the observed enrichments most probably stem from considerable oxygen consumption during photosynthesis even when major O₂-consuming reactions such as photorespiration were minimized. These enrichments increased linearly with rising O₂ levels but with different δ¹⁷O/δ¹⁸O slopes for the various organisms, suggesting engagements of different O₂-consuming reactions with rising O₂ levels. Consumption of O₂ may be important for energy dissipation during photosynthesis. The isotope enrichment observed here, not accounted for in earlier assessments, closes an important gap in our understanding of the difference between the isotopic compositions of atmospheric oxygen and that of seawater, i.e., the Dole effect.     

AMP-activated protein kinase plays a role in initiating metabolic rate suppression in goldfish hepatocytes

In the present study, we test the hypothesis that AMP-activated protein kinase (AMPK) initiates metabolic rate suppression in isolated goldfish hepatocytes. To accomplish this, we attempted to pharmacologically activate AMPK in goldfish hepatocytes with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) and the thienopyridone, A769662, to examine the effects of AMPK activation on eukaryotic elongation factor-2 (eEF2), protein synthesis, and cellular oxygen consumption rate ( [(M)\dot]_{\textO 2} \dot{M}_{{{\text{O}}_{ 2} }} ). Goldfish hepatocytes treated with 1 mM AICAR under normoxic conditions (>200 μM O₂) showed a modest but significant 1.1-fold increase in AMPK phosphorylation, a 7.5-fold increase in AMPK activity, a 1.4-fold increase in eEF2 phosphorylation, and a 24% decrease in [(M)\dot]_{\textO 2} \dot{M}_{{{\text{O}}_{ 2} }} . At physiologically relevant [O₂] (<40 μM O₂), the addition of 1 mM AICAR resulted in only a 13% decrease in cellular [(M)\dot]_{\textO 2} \dot{M}_{{{\text{O}}_{ 2} }} with no change in sensitivity to [O₂] as assessed by estimates of cellular P₅₀ and P₉₀ values. The addition of compound C, a general protein kinase inhibitor, after AICAR incubation did not reverse the effects of AICAR on [(M)\dot]_{\textO 2} \dot{M}_{{{\text{O}}_{ 2} }} in normoxia. Treatment of hepatocytes with ≤200 μM A769662 did not affect AMPK activity, AMPK phosphorylation, eEF2 phosphorylation, or cellular [(M)\dot]_{\textO 2} \dot{M}_{{{\text{O}}_{ 2} }} . These data suggest that A769662 is not an activator of AMPK in goldfish hepatocytes. Although our study provides support for the hypothesis that AMPK plays a role in initiating metabolic rate suppression in goldfish hepatocytes, this support must be viewed cautiously because of the known off-target effects of the pharmacological agents used.     

A 200-year coral stable oxygen isotope record from a high-latitude reef off Western Australia

 A core from a coral colony of Porites lutea was analysed for stable oxygen isotopic composition^*. A 200-year proxy record of sea surface temperatures from the Houtman Abrolhos Islands off west Australia was obtained from coral δ¹⁸O. At 29′S, the Houtman Abrolhos are the southernmost major reef complex of the Indian Ocean. They are located on the path of the Leeuwin Current, a southward flow of warm, tropical water, which is coupled to Indonesian throughflow. Coral δ¹⁸O primarily reflects local oceanographic and climatic variability, which is largely determined by spatial variability of the Leeuwin Current. However, coherence between coral δ¹⁸O and the current strength itself is relatively weak. Evolutionary spectral and singular spectrum analyses of coral δ¹⁸O demonstrate a high variability in spectral composition through time. Oscillations in the 5–7-y, 14–15-y, and quasi-biennial bands reflect teleconnections of local sea surface temperature (SST) to tropical Pacific climate variability. Deviations between local (coral-based) and regional (instrument) SST contain a cyclic component with a period of 15 y. Coral δ¹⁸O suggests a rise in SST by 0.6 ′C since AD 1944, consistent with available instrumental SST records. A long-term warming by 1.4 ′C since AD 1795 is inferred from the coral record. Accepted: 3 July 1998     

The intramolecular δ<Superscript>15</Superscript>N of lysine responds to respiratory status in <Emphasis Type="Italic">Paracoccus denitrificans</Emphasis>

Summary. Presented here is the first experimental evidence that natural, intramolecular, isotope ratios are sensitive to physiological status, based on observations of intramolecular δ¹⁵N of lysine in the mitochondrial mimic Paracoccus denitrificans. Paracoccus denitrificans, a versatile, gram-negative bacterium, was grown either aerobically or anaerobically on isotopically-characterized ammonium as sole cell-nitrogen source. Nitrogen isotope composition of the biomass with respect to source ammonium was = −6.2 ± 1.2‰ for whole cells under aerobic respiration, whereas cells grown anaerobically produced no net fractionation ( = −0.3 ± 0.23‰). Fractionation of ¹⁵N between protein nitrogen and total cell nitrogen increased during anaerobic respiration and suggests that residual nitrogen-containing compounds in bacterial cell membranes are isotopically lighter under anaerobic respiration. In aerobic cells, the lysine intramolecular difference between peptide and sidechain nitrogen is negligible, but in anaerobic cells was a remarkable Δ¹⁵N_{p − s} = δ¹⁵N_peptide − δ¹⁵N_sidechain = +11.0‰, driven predominantly by enrichment at the peptide N. Consideration of known lysine pathways suggests this to be likely due to enhanced synthesis of peptidoglycans in the anaerobic state. These data indicate that distinct pathway branching ratios associated with microbial respiration can be detected by natural intramolecular Δδ¹⁵N measurements, and are the first in vivo observations of position-specific measurements of nitrogen isotope fractionation.     

Molecular dynamics simulations of nafion and sulfonated poly ether sulfone membranes II. Dynamic properties of water and hydronium

We measured the self-diffusion coefficients of water in a Nafion membrane and two sulfonated polyethersulfone (SPES) membranes with varying ion-exchange capacities (IEC) in terms of relative humidity using the pulse field gradient NMR (PFG-NMR) technique. The self-diffusion coefficients were plotted against the number of water molecules per sulfonic acid group, λ, and compare these values with the results of molecular dynamics (MD) simulations. Classical MD simulations for all membranes were carried out using a consistent force field at λ = 3, 6, 9, 12, and 15. The dynamic properties of water (H₂O) and hydronium (H₃O⁺) on a molecular level were estimated as self-diffusion coefficients and residence times around a sulfonate group ( \textSO₃^- {\text{SO}}_3^{-} ). The diffusion coefficients of H₂O and H₃O⁺ followed the order, Nafion > SPES with IEC = 1.4 > SPES with IEC = 1.0 > SPES with IEC = 0.75, which agreed with the experimental data. The residence time distribution of H₂O around \textSO₃^- {\text{SO}}_3^{-} in Nafion was in the range of 1–6 ps, whereas H₂O in the SPES exhibited a residence time of greater than 20 ps.