Search

The Laacher See eruption (LSE) in Germany ranks among Europe’s largest volcanic events of the Upper Pleistocene1,2. Although tephra deposits of the LSE represent an important isochron for the synchronization of proxy archives at the Late Glacial to Early Holocene transition3, uncertainty in the age of the eruption has prevailed4. Here we present dendrochronological and radiocarbon measurements of subfossil trees that were buried by pyroclastic deposits that firmly date the LSE to 13,006 ± 9 calibrated years before present (bp; taken as ad 1950), which is more than a century earlier than previously accepted. The revised age of the LSE necessarily shifts the chronology of European varved lakes5,6 relative to the Greenland ice core record, thereby dating the onset of the Younger Dryas to 12,807 ± 12 calibrated years bp, which is around 130 years earlier than thought. Our results synchronize the onset of the Younger Dryas across the North Atlantic–European sector, preclude a direct link between the LSE and Greenland Stadial-1 cooling7, and suggest a large-scale common mechanism of a weakened Atlantic Meridional Overturning Circulation under warming conditions8–10.A revised date for the Laacher See eruption using measurements of subfossil trees shifts the chronology of European varved lakes relative to the Greenland ice core record, synchronizing the onset of the Younger Dryas across the North Atlantic–European sector. [ABSTRACT FROM AUTHOR]

Using a portable gas analyzer system, the geogenic gas regime below and around an ancient gate to hell at Hierapolis/Phrygia was characterized. The site was first described by Strabo and Plinius as a gate to the underworld. During centuries, it attracted even ancient tourists. In a grotto below the temple of Pluto, CO2 was found to be at deadly concentrations of up to 91%. Astonishingly, these vapors are still emitted in concentrations that nowadays kill insects, birds, and mammals. The concentrations of CO2 escaping from the mouth of the grotto to the outside atmosphere are still in the range of 4–53% CO2 depending on the height above ground level. They reach concentrations during the night that would easily kill even a human being within a minute. These emissions are thought to reflect the Hadean breath and/or the breath of the hellhound Kerberos guarding the entrance to hell. The origin of the geogenic CO2 is the still active seismic structure that crosses the old town of ancient Hierapolis as part of the Babadag fracture zone. Our measurements confirm the presence of geogenic CO2 in concentrations that explain ancient stories of killed bulls, rams, and songbirds during religious ceremonies. They also strongly corroborate that at least in the case of Hierapolis, ancient writers like Strabo or Plinius described a mystic phenomenon very exactly without much exaggeration. Two thousand years ago, only supernatural forces could explain these phenomena from Hadean depths whereas nowadays, modern techniques hint to the well-known phenomenon of geogenic CO2 degassing having mantle components with relatively higher helium and radon concentrations. [ABSTRACT FROM AUTHOR]

Four lichen species, Parmelia sulcata Taylor, Hypogymnia physodes (L.) Nyl., Cetraria islandica (L.) Ach., and Bryoria fuscescens (Gyelnik) Brodo and Hawksworth were exposed during autumn and winter at different sites of the Erzgebirge (Ore Mountains), the Fichtelgebirge and control sites. All lichens tested became visibly damaged with time. Thallus bleaching started from the edges and went on to the centre of the thallus. Sites of facilitated gas exchange like the soralia of P. sulcata and the pseudocyphelles of C. islandica became preferentially bleached. The sulfate concentration increased with exposure time reaching 200% of unpolluted controls. In contrast to coniferous trees (e.g. Picea abies), further exposure lead to a reduction in the S-concentration in the lichens, as sulfate and other intracellular metabolites were leached from the thalli due to membrane damage. The changes in the K-concentration proved to be an excellent measure for membrane leakiness; it was correlated with time of exposure and with SO2 concentrations at the different sites. Photosynthetic capacity and respiration were also strongly affected. Depending on the SO2-dose, the Bryoria species were unable to photosynthesize as early as 4–8 weeks after exposure, whereas Cetraria and Hypogymnia showed clear reduction in their ability to photoreduce CO2 within 8–10 weeks of exposure in the field. Parmelia sulcata was found to be the most tolerant species. After 3–4 months, photosynthesis was reduced by only 30%. The bioindicative value of these observations is discussed. [ABSTRACT FROM AUTHOR]

The photosynthetic properties of a range of lichens containing both green algal (11 species) and cyanobacterial (6 species) photobionts were examined with the aim of determining if there was clear evidence for the operation of a CO-concentrating mechanism (CCM) within the photobionts. Using a CO-gas-exchange system, which allowed resolution of fast transients, evidence was obtained for the existence of an inorganic carbon pool which accumulated in the light and was released in the dark. The pool was large (500-1000 nmol · mg Chl) in cyanobacterial lichens and about tenfold smaller in green algal lichens. In Hypogymnia physodes (L.) Nyl., which contains the green alga Trebouxia jamesii, a small inorganic carbon pool was rapidly formed in the light. Carbon dioxide was released from this pool into the gas phase upon darkening within about 20 s when photosynthesis was inhibited by the carbon-reduction-cycle inhibitor glycolaldehyde. In the absence of this inhibitor, release appeared to be obscured by carboxylation of ribulose bisphosphate. The kinetics of CO uptake and release were monophasic. The operation of an active CCM could be distinguished from passive accumulation and release accompanying the reversible light-dependent alkalization of the stroma by the presence of saturation characteristics with respect to external CO. In Peltigera canina (L.) Willd., which contains the cyanobacterium Nostoc sp., a larger CO pool was taken up over a longer period in the light and the release of this pool in the dark was slow, lasting 3-5 min. This pool also accumulated in the presence of glycolaldehyde, and under these conditions the CO release was biphasic. In both species, photosynthesis at low CO was inhibited by the carbonic-anhydrase inhibitor ethoxyzolamide (EZ). Inhibition could be reversed fully or to a considerable extent by high CO. In Peltigera, EZ decreased both the accumulation of the CO pool by the CCM and the rate of photosynthesis. Free-living cultures of Nostoc sp. showed a similar effect of EZ on photosynthesis, although it was more dramatic than that seen with the lichen thalli. In contrast, in Hypogymnia, EZ actually increased the size of the CO pool, although it inhibited photosynthesis. This effect was also seen when glycolaldehyde was present together with EZ. Surprisingly, EZ did not alter the kinetics of either CO uptake or release. Taken together, the evidence indicates the operation in cyanobacterial lichens of a CCM which is capable of considerable elevation of internal CO and is similar to that reported for free-living cyanobacteria. The CCM of green algal lichens accumulates much less CO and is probably less effective than that which operates in cyanobacterial lichens. [ABSTRACT FROM AUTHOR]

Midday depression of net photosynthesis and transpiration in the Mediterranean sclerophylls Arbutus unedo L. and Quercus suber L. occurs with a depression of mesophyll photosynthetic activity as indicated by calculated carboxylation efficiency (CE) and constant diurnal calculated leaf intercellular partial pressure of CO (C). This work examines the hypothesis that this midday depression can be explained by the distribution of patches of either wide-open or closed stomata on the leaf surface, independent of a coupling mechanism between stomata and mesophyll that results in a midday depression of photosynthetic activity of the mesophyll. Pressure infiltration of four liquids differing in their surface tension was used as a method to show the occurrence of stomatal patchiness and to determine the status of stomatal aperture within the patches. Liquids were selected such that the threshold leaf conductance necessary for infiltration through the stomatal pores covered the expected diurnal range of calculated leaf conductance (g) for these species. Infiltration experiments were carried out with leaves of potted plants under simulated Mediterranean summer conditions in a growth chamber. For all four liquids, leaves of both species were found to be fully infiltratable in the morning and in the late afternoon while during the periods leading up to and away from midday the leaves showed a pronounced patchy distribution of infiltratable and non-infiltratable areas. Similar linear relationships between the amount of liquid infiltrated and g (measured by porometry prior to detachment and infiltration) for all liquids clearly revealed the existence of pneumatically isolated patches containing only wide-open or closed stomata. The good correspondence between the midday depression of CE, calculated under the assumption of no stomatal patchiness, and the diurnal changes in non-infiltratable leaf area strongly indicates that the apparent reduction in mesophyll activity results from assuming no stomatal patchiness. It is suggested that simultaneous responses of stomata and mesophyll activity reported for other species may also be attributed to the occurrence of stomatal patchiness. In Quercus coccifera L., where the lack of constant diurnal calculated C and major depression of measured CE at noontime indicates different stomatal behavior, non-linear and dissimilar relationships between g and the infiltratable quantities of the four liquids were found. This indicates a wide distribution of stomatal aperture on the leaf surface rather than only wide-open or closed stomata. [ABSTRACT FROM AUTHOR]

Using experimental information obtained in earlier studies on cellular buffering and SO uptake into leaves (Pfanz and Heber, 1986, Plant Physiol. 81, 597-602; Pfanz et al., 1987 a, b, Plant Physiol.), a mathematical model is presented which permits computer analysis of the transport of SO from the atmosphere into the mesophyll of leaves and describes the intracellular distribution of hydration products of SO. Oxidation of sulfite and metabolization of sulfate can also be included. Although the model does not attempt to incorporate all available information on the intracellular transport of sulfur species, it permits general conclusions in regard to cellular responses to SO. The model can be extended and modified for gases other than SO. Examples are presented to illustrate the information the model is able to give. Times required for SO equilibration are long. Equilibrium relationships between SO in the atmosphere and cellular SO show that in order to survive in even slightly contaminated air, leaves must prevent equilibration between external and internal SO. [ABSTRACT FROM AUTHOR]