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Christoph Leuschner - One of the best experts on this subject based on the ideXlab platform.
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The Role of Low Soil Temperature for Photosynthesis and Stomatal Conductance of Three Graminoids From Different Elevations.
Frontiers in plant science, 2019Co-Authors: Leonie Göbel, Heinz Coners, Dietrich Hertel, Sandra Willinghöfer, Christoph LeuschnerAbstract:In high-elevation grasslands, plants can encounter periods with high air temperature while the soil remains cold, which may lead to a temporary mismatch in the physiological activity of leaves and roots. In a climate chamber experiment with Graminoid species from three elevations (4400, 2400, and 250 m a.s.l.), we tested the hypothesis that soil temperature can influence photosynthesis and stomatal conductance independently of air temperature. Soil monoliths with swards of Kobresia pygmaea (high alpine), Nardus stricta (lower alpine), and Deschampsia flexuosa (upper lowland) were exposed to soil temperatures of 25, 15, 5, and -2°C and air temperatures of 20 and 10°C for examining the effect of independent soil and air temperature variation on photosynthesis, leaf dark respiration, and stomatal conductance and transpiration. Soil frost (-2°C) had a strong negative effect on gas exchange and stomatal conductance in all three species, independent of the elevation of origin. Leaf dark respiration was stimulated by soil frost in D. flexuosa, but not in K. pygmaea, which also had a lower temperature optimum of photosynthesis. Soil cooling from 15 to 5°C did not significantly reduce stomatal conductance and gas exchange in any of the species. We conclude that all three Graminoids are able to maintain a relatively high root water uptake in cold, non-frozen soil, but the high-alpine K. pygmaea seems to be especially well adapted to warm shoot - cold root episodes, as it has a higher photosynthetic activity at 10 than 20°C air temperature and does not up-regulate leaf dark respiration upon soil freezing, as was observed in the grasses from warmer climates.
Matthew J. Wooller - One of the best experts on this subject based on the ideXlab platform.
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Pleistocene Graminoid-dominated ecosystems in the Arctic
Quaternary Science Reviews, 2011Co-Authors: Mikhail S. Blinnikov, Benjamin V. Gaglioti, Matthew J. Wooller, Donald A. Walker, Grant D. ZazulaAbstract:Abstract We review evidence obtained from analyses of multiple proxies (floristics, mammal remains, paleoinsects, pollen, macrofossils, plant cuticles, phytoliths, stable isotopes, and modeling) that elucidate the composition and character of the Graminoid-dominated ecosystems of the Pleistocene Arctic. The past thirty years have seen a renewed interest in this now-extinct biome, sometimes referred to as “tundra-steppe” (steppe-tundra in North American sources). While many questions remain, converging evidence from many new terrestrial records and proxies coupled with better understanding of paleoclimate dynamics point to the predominance of xeric and cold adapted grassland as the key former vegetation type in the Arctic confirming earlier conjectures completed in the 1960s–1980s. A variety of still existing species of grasses and forbs played key roles in the species assemblages of the time, but their mixtures were not analogous to the tundras of today. Local mosaics based on topography, proximity to the ice sheets and coasts, soil heterogeneity, animal disturbance, and fire regimes were undoubtedly present. However, inadequate coverage of terrestrial proxies exist to resolve this spatial heterogeneity. These past ecosystems were maintained by a combination of dry and cold climate and grazing pressure/disturbance by large (e.g., mammoth and horse) and small (e.g., ground squirrels) mammals. Some recent studies from Eastern Beringia (Alaska) suggest that more progress will be possible when analyses of many proxies are combined at local scales.
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Developing Graminoid cuticle analysis for application to Beringian palaeoecology
Review of Palaeobotany and Palynology, 2010Co-Authors: Benjamin V. Gaglioti, K. Severin, Matthew J. WoollerAbstract:Abstract Much of Beringia was composed of Graminoid (grass and sedge) dominated habitats during the Late-Pleistocene, yet the account of the actual gramioids that were present is relatively vague. The spatial and temporal variabilities of palaeoclimate, mega-fauna, archaeology, and vegetation interactions could be significantly enhanced with accounts of Beringian Graminoids. Fossil Graminoid foliage is well preserved in permafrost sediments from Beringia and is available for identification using the micro-morphologies of the leaf epidermis (cuticles), which are often consistent with taxonomic identity. We present a scanning electron microscope (SEM) guide to the leaf cuticles of 38 Graminoid species shown to be, or suspected of being present in former Eastern Beringian habitats during marine isotope stages (MIS) 2 and 3 (∼ 56,000–12,000 cal. yrs BP). We examine whether modern specimens have sufficient cuticle variability to identify fossil foliage. We surveyed SEM images from herbarium specimens for 50 quantitative and qualitative features on both sides (adaxial and abaxial) of leaves, and entered these into an interactive key program (Delta Editor). Individual species were unique based on the combined presence of 2–4 cuticle features. Replicate samples (n = 5) of 10 species were integrated into a cluster analysis and visually compared using a dendrogram. Overall, fossils that match modern specimens with a Gower's similarity coefficient of 0.80 or higher can be considered a reliable identification match. Several fossil Graminoid specimens were compared and identified with our reference collection. Cuticle identification appears to be a viable method for future macrofossil analysis in Beringia.
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Changes in Graminoid stomatal morphology over the last glacial-interglacial transition: evidence from Mount Kenya, East Africa
Palaeogeography Palaeoclimatology Palaeoecology, 2001Co-Authors: Matthew J. Wooller, A. D. Q. AgnewAbstract:Abstract Stomatal size and density were measured from Graminoid cuticular fragments extracted from dated sediments in two tropical-montane crater lakes on Mount Kenya. The sediments had been dated in other studies and spanned 1500–37 000 calibrated years BP. Changes in the mean size and density of the Graminoid stomata were found. Using a coarse signal analysis the two lakes gave fairly similar results, although there was some divergence at the start and end of the time period analyzed. There is some correspondence between the atmospheric CO 2 concentration and Graminoid stomatal density during the transition from the LGM to the start of the Holocene, where stomatal density decreased while CO 2 concentrations increased. All the changes observed may have been plastic responses within existing species at the site or competitive replacements of grass floras. We argue that higher stomatal density may have been a response to falling CO 2 levels during the last glaciation, accompanying the replacement of a C 3 flora by C 4 species. The stomatal size changes exhibited over this time period may have adapted plants to changes in soil water availability. That stomatal morphology changes in a sample flora (not a single taxon) over millennia is a novel finding, and one that may have implications for paleoecological interpretation and the prediction of grass behavior in the future.
Richard D Bardgett - One of the best experts on this subject based on the ideXlab platform.
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warming effects on greenhouse gas fluxes in peatlands are modulated by vegetation composition
Ecology Letters, 2013Co-Authors: Susan E Ward, Nick Ostle, Simon Oakley, Helen Quirk, Peter A Henrys, Richard D BardgettAbstract:Understanding the effects of warming on greenhouse gas feedbacks to climate change represents a major global challenge. Most research has focused on direct effects of warming, without considering how concurrent changes in plant communities may alter such effects. Here, we combined vegetation manipulations with warming to investigate their interactive effects on greenhouse gas emissions from peatland. We found that although warming consistently increased respiration, the effect on net ecosystem CO2 exchange depended on vegetation composition. The greatest increase in CO2 sink strength after warming was when shrubs were present, and the greatest decrease when Graminoids were present. CH4 was more strongly controlled by vegetation composition than by warming, with largest emissions from Graminoid communities. Our results show that plant community composition is a significant modulator of greenhouse gas emissions and their response to warming, and suggest that vegetation change could alter peatland carbon sink strength under future climate change.
Anthony Joern - One of the best experts on this subject based on the ideXlab platform.
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Foliar phenolics of nebraska sandhills prairie Graminoids: Between-years, seasonal, and interspecific variation.
Journal of chemical ecology, 1993Co-Authors: Simon Mole, Anthony JoernAbstract:Because of their potential as antiherbivore defenses, plant phenolics elicit considerable attention. We made quantitative and qualitative analyses of phenolics, alkaloids, cyanogenic glycosides, and saponins in the dominant Graminoids of a Nebraska Sandhills prairie. We examined the foliage of seven species:Agropyron smithii Rydb.,Andropogon hallii Hack.,Andropogon scoparius Michx.,Bouteloua gracilis (H.B.K) Lag. ex Griffiths,Calamovilfa longifolia (Hook.) Scribn.,Carex heliophila Mack., andStipa comata Trin & Rupr. Their leaves contain low levels of phenolics that vary significantly among species. A more detailed examination of the three species with the highest levels of phenolics showed among-year, seasonal, and spatial heterogeneity in the levels of total phenolics. In all seven species, the majority of the specific phenolics present have the Chromatographic properties of phenylpropanoids and are likely to be present as sugar-linked derivatives such as free glycosides or cell wall-bound phenolics. These species do not contain condensed tannins. The absence of other common kinds of secondary metabolites indicates that these Graminoids are unlikely to have significant chemical defenses, at least in terms of substances likely to be active against mammalian herbivores. In this, they exemplify the situation thought typical for prairie Graminoids.
Grant D. Zazula - One of the best experts on this subject based on the ideXlab platform.
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Pleistocene Graminoid-dominated ecosystems in the Arctic
Quaternary Science Reviews, 2011Co-Authors: Mikhail S. Blinnikov, Benjamin V. Gaglioti, Matthew J. Wooller, Donald A. Walker, Grant D. ZazulaAbstract:Abstract We review evidence obtained from analyses of multiple proxies (floristics, mammal remains, paleoinsects, pollen, macrofossils, plant cuticles, phytoliths, stable isotopes, and modeling) that elucidate the composition and character of the Graminoid-dominated ecosystems of the Pleistocene Arctic. The past thirty years have seen a renewed interest in this now-extinct biome, sometimes referred to as “tundra-steppe” (steppe-tundra in North American sources). While many questions remain, converging evidence from many new terrestrial records and proxies coupled with better understanding of paleoclimate dynamics point to the predominance of xeric and cold adapted grassland as the key former vegetation type in the Arctic confirming earlier conjectures completed in the 1960s–1980s. A variety of still existing species of grasses and forbs played key roles in the species assemblages of the time, but their mixtures were not analogous to the tundras of today. Local mosaics based on topography, proximity to the ice sheets and coasts, soil heterogeneity, animal disturbance, and fire regimes were undoubtedly present. However, inadequate coverage of terrestrial proxies exist to resolve this spatial heterogeneity. These past ecosystems were maintained by a combination of dry and cold climate and grazing pressure/disturbance by large (e.g., mammoth and horse) and small (e.g., ground squirrels) mammals. Some recent studies from Eastern Beringia (Alaska) suggest that more progress will be possible when analyses of many proxies are combined at local scales.
