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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
    Métadonnées seulement
    Seasonal patterns of testate amoeba diversity, community structure and species-environment relationships in four Sphagnum-dominated peatlands along a 1300 m altitudinal gradient in Switzerland
    (2013)
    Lamentowicz, Mariusz
    ;
    Bragazza, Luca
    ;
    Buttler, Alexandre
    ;
    Jassey, V. E. J.
    ;
    Mitchell, Edward 
    Altitudinal gradients are useful to study the potential effects of climate change on ecosystems. Historically, studies on elevation gradients have primarily focused on macro-organisms and ecosystem processes, while microorganisms have been mostly ignored despite their ubiquity and functional importance. We studied the temporal (about every two months from June 2008 until May 2009) variation of testate amoeba communities in four Sphagnum-dominated peatlands along a 1300 to elevation gradient in the Swiss Mountains (580-1880 m) in relation to water table depth and hydrochemistry with special focus on dissolved organic carbon (DOC), a useful proxy for changes in C-cycling in peatlands. The lowest site had significantly (P < 0.01) lowest testate amoeba density, species richness. The highest site had highest testate amoeba density (38 ind mg(-1) dry mass of Sphagnum). Seasonal fluctuations in testate amoeba species richness and diversity were not consistent among sites but density tended to peak in spring at all sites, autumn in the three highest sites and mid-winter in the upper two sites. In a redundancy analysis (RDA) community structure was more strongly correlated to altitude (33.8% of variance explained in living community) than to soil hydrological and hydro-chemical variables (together explaining 16.2% of variance). In a partial RDA with altitude used as covariable, the four sites were separated by DOP, DOC, DON, pH and average depth to water table. The abundance of high trophic level testate amoeba species (shell-aperture over their body size >0.20; i.e. primarily predators of protists and micro-metazoa) as well as the community size structure increased from lowest to highest elevation (respectively by 3.7x and 6x) and followed the seasonal patterns of total density, while DOC, DON, and DOC/DON decreased with elevation. These results agree with previously reported alteration of peatland microbial food chains in response to experimental warming, suggesting that climate-induced changes in microbial community structure (here a shortening of microbial food chains) represent a mechanism controlling the carbon balance of peatlands. (C) 2013 Elsevier Ltd. All rights reserved.
  • Publication
    Métadonnées seulement
    Climatic modifiers of the response to nitrogen deposition in peat-forming Sphagnum mosses: a meta-analysis
    (2011)
    Limpens, J.
    ;
    Granath, G.
    ;
    Gunnarsson, U.
    ;
    Aerts, R.
    ;
    Bayley, S.
    ;
    Bragazza, Luca
    ;
    Bubier, J.
    ;
    Buttler, Alexandre
    ;
    van den Berg, L. J. L.
    ;
    Francez, Andre-Jean
    ;
    Gerdol, R.
    ;
    Grosvernier, Philippe
    ;
    Heijmans, M. M. P. D.
    ;
    Hoosbeek, M. R.
    ;
    Hotes, S.
    ;
    Ilomets, M.
    ;
    Leith, I.
    ;
    Mitchell, Edward 
    ;
    Moore, T.
    ;
    Nilsson, Mats B.
    ;
    Nordbakken, J. F.
    ;
    Rochefort, L.
    ;
    Rydin, H.
    ;
    Sheppard, L. J.
    ;
    Thormann, M.
    ;
    Wiedermann, M. M.
    ;
    Williams, B. L.
    ;
    Xu, B.
    Peatlands in the northern hemisphere have accumulated more atmospheric carbon (C) during the Holocene than any other terrestrial ecosystem, making peatlands long-term C sinks of global importance. Projected increases in nitrogen (N) deposition and temperature make future accumulation rates uncertain. Here, we assessed the impact of N deposition on peatland C sequestration potential by investigating the effects of experimental N addition on Sphagnum moss. We employed meta-regressions to the results of 107 field experiments, accounting for sampling dependence in the data. We found that high N loading (comprising N application rate, experiment duration, background N deposition) depressed Sphagnum production relative to untreated controls. The interactive effects of presence of competitive vascular plants and high tissue N concentrations indicated intensified biotic interactions and altered nutrient stochiometry as mechanisms underlying the detrimental N effects. Importantly, a higher summer temperature (mean for July) and increased annual precipitation intensified the negative effects of N. The temperature effect was comparable to an experimental application of almost 4 g N m(-2) yr(-1) for each 1 degrees C increase. Our results indicate that current rates of N deposition in a warmer environment will strongly inhibit C sequestration by Sphagnum-dominated vegetation.