Publications by authors named "Wolfram M Kürschner"

11 Publications

  • Page 1 of 1

Astronomical age constraints and extinction mechanisms of the Late Triassic Carnian crisis.

Sci Rep 2017 05 31;7(1):2557. Epub 2017 May 31.

Department of Geosciences, University of Oslo, Oslo, 0371, Norway.

The geological record contains evidence for numerous pronounced perturbations in the global carbon cycle, some of which are associated with mass extinction. In the Carnian (Late Triassic), evidence from sedimentology and fossil pollen points to a significant change in climate, resulting in biotic turnover, during a time termed the 'Carnian Pluvial Episode' (CPE). Evidence from the marine realm suggests a causal relationship between the CPE, a global 'wet' period, and the injection of light carbon into the atmosphere. Here we provide the first evidence from a terrestrial stratigraphic succession of at least five significant negative C-isotope excursions (CIE)'s through the CPE recorded in both bulk organic carbon and compound specific plant leaf waxes. Furthermore, construction of a floating astronomical timescale for 1.09 Ma of the Late Triassic, based on the recognition of 405 ka eccentricity cycles in elemental abundance and gamma ray (GR) data, allows for the estimation of a duration for the isotope excursion(s). Source mixing calculations reveal that the observed substantial shift(s) in δC was most likely caused by a combination of volcanic emissions, subsequent warming and the dissociation of methane clathrates.
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http://dx.doi.org/10.1038/s41598-017-02817-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5451402PMC
May 2017

Multi-Year Leaf-Level Response to Sub-Ambient and Elevated Experimental CO2 in Betula nana.

PLoS One 2016 10;11(6):e0157400. Epub 2016 Jun 10.

Palaeoecology, Department of Physical Geography, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands.

The strong link between stomatal frequency and CO2 in woody plants is key for understanding past CO2 dynamics, predicting future change, and evaluating the significant role of vegetation in the hydrological cycle. Experimental validation is required to evaluate the long-term adaptive leaf response of C3 plants to CO2 conditions; however, studies to date have only focused on short-term single-season experiments and may not capture (1) the full ontogeny of leaves to experimental CO2 exposure or (2) the true adjustment of structural stomatal properties to CO2, which we postulate is likely to occur over several growing seasons. We conducted controlled growth chamber experiments at 150 ppmv, 450 ppmv and 800 ppmv CO2 with woody C3 shrub Betula nana (dwarf birch) over two successive annual growing seasons and evaluated the structural stomatal response to atmospheric CO2 conditions. We find that while some adjustment of leaf morphological and stomatal parameters occurred in the first growing season where plants are exposed to experimental CO2 conditions, amplified adjustment of non-plastic stomatal properties such as stomatal conductance occurred in the second year of experimental CO2 exposure. We postulate that the species response limit to CO2 of B. nana may occur around 400-450 ppmv. Our findings strongly support the necessity for multi-annual experiments in C3 perennials in order to evaluate the effects of environmental conditions and provide a likely explanation of the contradictory results between historical and palaeobotanical records and experimental data.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0157400PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4902311PMC
July 2017

Aberrant Classopollis pollen reveals evidence for unreduced (2n) pollen in the conifer family Cheirolepidiaceae during the Triassic-Jurassic transition.

Proc Biol Sci 2013 Oct 7;280(1768):20131708. Epub 2013 Aug 7.

Department of Geosciences and Centre for Earth Evolution and Dynamics, University of Oslo, PO Box 1047, 0316 Oslo, Norway.

Polyploidy (or whole-genome doubling) is a key mechanism for plant speciation leading to new evolutionary lineages. Several lines of evidence show that most species among flowering plants had polyploidy ancestry, but it is virtually unknown for conifers. Here, we study variability in pollen tetrad morphology and the size of the conifer pollen type Classopollis extracted from sediments of the Triassic-Jurassic transition, 200 Ma. Classopollis producing Cheirolepidiaceae were one of the most dominant and diverse groups of conifers during the Mesozoic. We show that aberrant pollen Classopollis tetrads, triads and dyads, and the large variation in pollen size indicates the presence of unreduced (2n) pollen, which is one of the main mechanisms in modern polyploid formation. Polyploid speciation may explain the high variability of growth forms and adaptation of these conifers to different environments and their resistance to extreme growth conditions. We suggest that polyploidy may have also reduced the extinction risk of these conifers during the End-Triassic biotic crisis.
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http://dx.doi.org/10.1098/rspb.2013.1708DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3757988PMC
October 2013

Stable Carbon and Nitrogen Isotopes in a Peat Profile Are Influenced by Early Stage Diagenesis and Changes in Atmospheric CO(2) and N Deposition.

Water Air Soil Pollut 2012 Jun 25;223(5):2007-2022. Epub 2012 Jan 25.

In this study, we test whether the δ(13)C and δ(15)N in a peat profile are, respectively, linked to the recent dilution of atmospheric δ(13)CO(2) caused by increased fossil fuel combustion and changes in atmospheric δ(15)N deposition. We analysed bulk peat and Sphagnum fuscum branch C and N concentrations and bulk peat, S. fuscum branch and Andromeda polifolia leaf δ(13)C and δ(15)N from a 30-cm hummock-like peat profile from an Aapa mire in northern Finland. Statistically significant correlations were found between the dilution of atmospheric δ(13)CO(2) and bulk peat δ(13)C, as well as between historically increasing wet N deposition and bulk peat δ(15)N. However, these correlations may be affected by early stage kinetic fractionation during decomposition and possibly other processes. We conclude that bulk peat stable carbon and nitrogen isotope ratios may reflect the dilution of atmospheric δ(13)CO(2) and the changes in δ(15)N deposition, but probably also reflect the effects of early stage kinetic fractionation during diagenesis. This needs to be taken into account when interpreting palaeodata. There is a need for further studies of δ(15)N profiles in sufficiently old dated cores from sites with different rates of decomposition: These would facilitate more reliable separation of depositional δ(15)N from patterns caused by other processes. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11270-011-1001-8) contains supplementary material, which is available to authorized users.
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http://dx.doi.org/10.1007/s11270-011-1001-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3359457PMC
June 2012

Atmospheric carbon injection linked to end-Triassic mass extinction.

Science 2011 Jul;333(6041):430-4

Palaeoecology, Institute of Environmental Biology, Faculty of Science, Utrecht University, Budapestlaan 4, NL-3584 CD, Utrecht, Netherlands.

The end-Triassic mass extinction (~201.4 million years ago), marked by terrestrial ecosystem turnover and up to ~50% loss in marine biodiversity, has been attributed to intensified volcanic activity during the break-up of Pangaea. Here, we present compound-specific carbon-isotope data of long-chain n-alkanes derived from waxes of land plants, showing a ~8.5 per mil negative excursion, coincident with the extinction interval. These data indicate strong carbon-13 depletion of the end-Triassic atmosphere, within only 10,000 to 20,000 years. The magnitude and rate of this carbon-cycle disruption can be explained by the injection of at least ~12 × 10(3) gigatons of isotopically depleted carbon as methane into the atmosphere. Concurrent vegetation changes reflect strong warming and an enhanced hydrological cycle. Hence, end-Triassic events are robustly linked to methane-derived massive carbon release and associated climate change.
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http://dx.doi.org/10.1126/science.1204255DOI Listing
July 2011

An explanation for conflicting records of Triassic-Jurassic plant diversity.

Proc Natl Acad Sci U S A 2010 Aug 16;107(35):15351-6. Epub 2010 Aug 16.

School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland.

Macrofossils (mostly leaves) and sporomorphs (pollen and spores) preserve conflicting records of plant biodiversity during the end-Permian (P-Tr), Triassic-Jurassic (Tr-J), and end-Cretaceous (K-T) mass extinctions. Estimates of diversity loss based on macrofossils are typically much higher than estimates of diversity loss based on sporomorphs. Macrofossils from the Tr-J of East Greenland indicate that standing species richness declined by as much as 85% in the Late Triassic, whereas sporomorph records from the same region, and from elsewhere in Europe, reveal little evidence of such catastrophic diversity loss. To understand this major discrepancy, we have used a new high-resolution dataset of sporomorph assemblages from Astartekløft, East Greenland, to directly compare the macrofossil and sporomorph records of Tr-J plant biodiversity. Our results show that sporomorph assemblages from the Tr-J boundary interval are 10-12% less taxonomically diverse than sporomorph assemblages from the Late Triassic, and that vegetation composition changed rapidly in the boundary interval as a result of emigration and/or extirpation of taxa rather than immigration and/or origination of taxa. An analysis of the representation of different plant groups in the macrofossil and sporomorph records at Astartekløft reveals that reproductively specialized plants, including cycads, bennettites and the seed-fern Lepidopteris are almost absent from the sporomorph record. These results provide a means of reconciling the macrofossil and sporomorph records of Tr-J vegetation change, and may help to understand vegetation change during the P-Tr and K-T mass extinctions and around the Paleocene-Eocene Thermal Maximum.
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http://dx.doi.org/10.1073/pnas.1004207107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2932585PMC
August 2010

A role for atmospheric CO2 in preindustrial climate forcing.

Proc Natl Acad Sci U S A 2008 Oct 6;105(41):15815-8. Epub 2008 Oct 6.

TNO Geological Survey of The Netherlands, Princetonlaan 6, 3584 CB Utrecht, The Netherlands.

Complementary to measurements in Antarctic ice cores, stomatal frequency analysis of leaves of land plants preserved in peat and lake deposits can provide a proxy record of preindustrial atmospheric CO(2) concentration. CO(2) trends based on leaf remains of Quercus robur (English oak) from the Netherlands support the presence of significant CO(2) variability during the first half of the last millennium. The amplitude of the reconstructed multidecadal fluctuations, up to 34 parts per million by volume, considerably exceeds maximum shifts measured in Antarctic ice. Inferred changes in CO(2) radiative forcing are of a magnitude similar to variations ascribed to other mechanisms, particularly solar irradiance and volcanic activity, and may therefore call into question the concept of the Intergovernmental Panel on Climate Change, which assumes an insignificant role of CO(2) as a preindustrial climate-forcing factor. The stomata-based CO(2) trends correlate with coeval sea-surface temperature trends in the North Atlantic Ocean, suggesting the possibility of an oceanic source/sink mechanism for the recorded CO(2) changes.
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http://dx.doi.org/10.1073/pnas.0807624105DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2562417PMC
October 2008

The impact of Miocene atmospheric carbon dioxide fluctuations on climate and the evolution of terrestrial ecosystems.

Proc Natl Acad Sci U S A 2008 Jan 3;105(2):449-53. Epub 2008 Jan 3.

Faculty of Science, Institute of Environmental Biology, Department of Palaeoecology, Laboratory of Palaeobotany and Palynology, Utrecht University, Budapestlaan 4, 3584 CD, Utrecht, The Netherlands.

The Miocene is characterized by a series of key climatic events that led to the founding of the late Cenozoic icehouse mode and the dawn of modern biota. The processes that caused these developments, and particularly the role of atmospheric CO2 as a forcing factor, are poorly understood. Here we present a CO2 record based on stomatal frequency data from multiple tree species. Our data show striking CO2 fluctuations of approximately 600-300 parts per million by volume (ppmv). Periods of low CO2 are contemporaneous with major glaciations, whereas elevated CO2 of 500 ppmv coincides with the climatic optimum in the Miocene. Our data point to a long-term coupling between atmospheric CO2 and climate. Major changes in Miocene terrestrial ecosystems, such as the expansion of grasslands and radiations among terrestrial herbivores such as horses, can be linked to these marked fluctuations in CO2.
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http://dx.doi.org/10.1073/pnas.0708588105DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2206556PMC
January 2008

Changes in stomatal frequency and size during elongation of Tsuga heterophylla needles.

Ann Bot 2004 Oct 20;94(4):561-9. Epub 2004 Aug 20.

Department of Palaeoecology, Laboratory of Palaeobotany and Palynology, Utrecht University, Budapestlaan 4, 3584 CD, The Netherlands.

Background And Aims: The inverse relationship between the number of stomata and atmospheric CO2 levels observed in different plant species is increasingly used for reconstructions of past CO2 concentrations. To validate this relationship, the potential influence of other environmental conditions and ontogenetical development stage on stomatal densities must be investigated as well. Quantitative data on the changes in stomatal density of conifers in relation to leaf development is reported.

Methods: Stomatal frequency and epidermal cells of Tsuga heterophylla needles during different stages of budburst were measured using computerized image analysis systems on light microscope slides.

Key Results: Stomata first appear in the apical region and subsequently spread basipetally towards the needle base during development. The number of stomatal rows on a needle does not change during ontogeny, but stomatal density decreases nonlinearly with increasing needle area, until about 50 % of the final needle area. The total number of stomata on the needle increases during the entire developmental period, indicating that stomatal and epidermal cell formation continues until the needle has matured completely.

Conclusions: Epidermal characteristics in developing conifer needles appear to be fundamentally different from angiosperm dicot leaves, where in general leaf expansion in the final stages is due to cell expansion rather than cell formation. The lack of further change in either stomatal density or stomatal density per millimetre needle length (the stomatal characteristic most sensitive to CO2 in conifers) in the final stages of leaf growth indicates that in conifers the stage of leaf maturation would not influence CO2 reconstructions based on stomatal density.
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http://dx.doi.org/10.1093/aob/mch175DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4242229PMC
October 2004

Environmental mutagenesis during the end-Permian ecological crisis.

Proc Natl Acad Sci U S A 2004 Aug 28;101(35):12952-6. Epub 2004 Jul 28.

Laboratory of Palaeobotany and Palynology, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands.

During the end-Permian ecological crisis, terrestrial ecosystems experienced preferential dieback of woody vegetation. Across the world, surviving herbaceous lycopsids played a pioneering role in repopulating deforested terrain. We document that the microspores of these lycopsids were regularly released in unseparated tetrads indicative of failure to complete the normal process of spore development. Although involvement of mutation has long been hinted at or proposed in theory, this finding provides concrete evidence for chronic environmental mutagenesis at the time of global ecological crisis. Prolonged exposure to enhanced UV radiation could account satisfactorily for a worldwide increase in land plant mutation. At the end of the Permian, a period of raised UV stress may have been the consequence of severe disruption of the stratospheric ozone balance by excessive emission of hydrothermal organohalogens in the vast area of Siberian Traps volcanism.
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http://dx.doi.org/10.1073/pnas.0404472101DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC516500PMC
August 2004

Stomatal frequency adjustment of four conifer species to historical changes in atmospheric CO2.

Am J Bot 2003 Apr;90(4):610-9

Laboratory of Palaeobotany and Palynology, Utrecht University, 3584 CD Utrecht, Netherlands;

The species-specific inverse relation between atmospheric CO(2) concentration and stomatal frequency for many woody angiosperm species is being used increasingly with fossil leaves to reconstruct past atmospheric CO(2) levels. To extend our limited knowledge of the responsiveness of conifer needles to CO(2) fluctuations, the stomatal frequency response of four native North American conifer species (Tsuga heterophylla, Picea glauca, Picea mariana, and Larix laricina) to a range of historical CO(2) mixing ratios (290 to 370 ppmV) was analyzed. Because of the specific mode of leaf development and the subsequent stomatal patterning in conifer needles, the stomatal index of these species was not affected by CO(2). In contrast, a new measure of stomatal frequency, based on the number of stomata per millimeter of needle length, decreased significantly with increasing CO(2). For Tsuga heterophylla, the stomatal frequency response to CO(2) changes in the last century is validated through assessment of the influence of other biological and environmental variables. Because of their sensitive response to CO(2), combined with a high preservation capacity, fossil needles of Tsuga heterophylla, Picea glauca, P. mariana, and Larix laricina have great potential for detecting and quantifying past atmospheric CO(2) fluctuations.
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http://dx.doi.org/10.3732/ajb.90.4.610DOI Listing
April 2003