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Mitchell, Edward

Nom
Mitchell, Edward
Affiliation principale
Site web
Fonction
Professeur ordinaire
Email
edward.mitchell@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/357
_
0000-0003-0358-506X

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  • Publication
    Accès libre
    Glasshouse vs field experiments: do they yield ecologically similar results for assessing N impacts on peat mosses?
    (2012)
    Limpens, J.
    ;
    Granath, G.
    ;
    Aerts, R.
    ;
    Heijmans, M. M. P. D.
    ;
    Sheppard, L. J.
    ;
    Bragazza, L.
    ;
    Williams, B. L.
    ;
    Rydin, H.
    ;
    Bubier, J.
    ;
    Moore, T.
    ;
    Rochefort, L.
    ;
    Mitchell, Edward 
    ;
    Buttler, A.
    ;
    van den Berg, L. J. L.
    ;
    Gunnarsson, U.
    ;
    Francez, A. -J.
    ;
    Gerdol, R.
    ;
    Thormann, M.
    ;
    Grosvernier, P.
    ;
    Wiedermann, M. M.
    ;
    Nilsson, M. B.
    ;
    Hoosbeek, M. R.
    ;
    Bayley, S.
    ;
    Nordbakken, J. -F.
    ;
    Paulissen, M. P. C. P.
    ;
    Hotes, S.
    ;
    Breeuwer, A.
    ;
    Ilomets, M.
    ;
    Tomassen, H. B. M.
    ;
    Leith, I.
    ;
    Xu, B.

    • Peat bogs have accumulated more atmospheric carbon (C) than any other terrestrial ecosystem today. Most of this C is associated with peat moss (Sphagnum) litter. Atmospheric nitrogen (N) deposition can decrease Sphagnum production, compromising the C sequestration capacity of peat bogs. The mechanisms underlying the reduced production are uncertain, necessitating multifactorial experiments.
    • We investigated whether glasshouse experiments are reliable proxies for field experiments for assessing interactions between N deposition and environment as controls on Sphagnum N concentration and production. We performed a meta-analysis over 115 glasshouse experiments and 107 field experiments.
    • We found that glasshouse and field experiments gave similar qualitative and quantitative estimates of changes in Sphagnum N concentration in response to N application. However, glasshouse-based estimates of changes in production – even qualitative assessments – diverged from field experiments owing to a stronger N effect on production response in absence of vascular plants in the glasshouse, and a weaker N effect on production response in presence of vascular plants compared to field experiments.
    • Thus, although we need glasshouse experiments to study how interacting environmental factors affect the response of Sphagnum to increased N deposition, we need field experiments to properly quantify these effects.
  • Publication
    Accès libre
    A near-annual palaeohydrological study based on testate amoebae from a sub-alpine mire: surface wetness and the role of climate during the instrumental period
    (2009)
    Lamentowicz, Mariucz
    ;
    van Der Knaap, Willem
    ;
    Lamentowicz, Lukasz
    ;
    van Leeuwen, Jacqueline F. N.
    ;
    Mitchell, Edward 
    ;
    Tomasz, Goslar
    ;
    Kamenik, Christian
    We present the first testate amoeba-based palaeohydrological reconstruction from the Swiss Alps, and the first depth to the water table (DWT) calibration dataset for this region. Compared to existing models, our new calibration dataset performs well (RMSEP = 4.88), despite the length of the water table gradient covered (53 cm). The present-day topography and vegetation of the study mire Mauntschas suggest that it is partly ombrotrophic (large Sphagnum fuscum hummocks, one of which was the coring site) but mostly under the minerotrophic influence of springs in the mire and runoff from the surrounding area. Ombrotrophic Sphagnum fuscum hummocks developed at the sampling site only during the last 50 years, when testate amoebae indicate a shift towards dry and/or acid conditions. Prior to AD 1950 the water table was much higher, suggesting that the influence of the mineral-rich water prevented the development of ombrotrophic hummocks. The reconstructed DWT correlated with Pinus cembra pollen accumulation rates, suggesting that testate amoebae living on the mire and P. cembra growing outside of it partly respond to the same factor(s). Finally, temperature trends from the nearby meteorological station paralleled trends in reconstructed DWT. However, contrary to other studies made on raised bogs of northwestern Europe, the highest correlation was observed for winter temperature, despite the fact that testate amoebae would more logically respond to moisture conditions during the growing season. The observed correlation with winter temperature might reflect a control of winter severity on surface moisture during at least the first part of the growing season, through snow melt and soil frost phenomena influencing run-off. More ecohydrological work on sub-alpine mires is needed to understand the relationships between climate, testate amoebae and peatland development.
  • Publication
    Accès libre
    Testate amoebae (Protists) as palaeoenvironmental indicators in peatlands
    (2005)
    Lamentowicz, Mariusz
    ;
    Mitchell, Edward 
    Testate amoebae (or testaceans, Testacea, Arcellaceans) are unicellular eukaryotic organisms living in freshwater or most terrestrial habitats such as soils, mosses, lakes, rivers, as well as brackish habitats such as estuaries. They are very abundant in Sphagnum mosses, where they live in the top part of mosses and the oxygenated part of the peat. The tests (shells) of Tesiacea are well preserved in peat and to a lesser extent in lake sediments. Efforts should be concentrated on constructing reliable regional transfer functions (mathematical representation of relation of species to environmental variables — presence of particular taxa in fossil material is the function of past environmental pa- rameters). as they exist for some world areas, and there is a complete lack of them for central Europe. Polish data are ex- ceptionally important because Poland is under several contrasted climatic influences — from oceanic to continental. The comparison of our data on climatic tendencies with those from Western Europe and the rest of the world will show how similar or different the responses of Polish peatlands might be. The paper has three aims: (a) to present the need for ecological studies on testate amoebae in Central Europe, (b) to show the potential of reconstruction of past environment on the basis ofmultiproxy studies that include testate amoebae as an in- tegral part of the palaeoecology toolbox and (c) to put our research efforts on testate amoebae in Poland in a more global perspective.