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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

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  • Publication
    Métadonnées seulement
    Ruptures multiples dans les tourbières du Jura: changements climatiques et hydrologiques, successions végétales et impacts humains
    (: DIALOGUES D'HISTOIRE ANCIENNE, 2002)
    Buttler, Alexandre
    ;
    Mitchell, Edward 
    ;
    Freléchoux, François
    ;
    Van der Knaap, Willem
    ;
    Van Leeuwen, Jacqueline
    ;
    Warner, Barry
    ;
    Gobat, Jean-Michel 
    ;
    Schweingruber, Fritz
    ;
    Amman, Brigitte
  • Publication
    Métadonnées seulement
    Biochemical characteristics of peat organic matter and distribution of testate amoebae in two naturally regenerating cutover Sphagnum peatlands of the Jura Mountains
    (2004)
    Laggoun-Défarge, Fatima
    ;
    Mitchell, Edward 
    ;
    Gilbert, Daniel
    ;
    Warner, Barry
    ;
    Comont, Laure
    ;
    Disnar, Jean-Robert
    ;
    Buttler, Alexandre
  • Publication
    Métadonnées seulement
  • Publication
    Métadonnées seulement
    Effects of elevated atmospheric CO2 and mineral nitrogen deposition on litter quality, bioleaching and decomposition in a sphagnum peat bog
    (: Springer, 1999-5-2)
    Siegenthaler, Andy
    ;
    Mitchell, Edward 
    ;
    Van der Heijden, Edvin
    ;
    Buttler, Alexandre
    ;
    Grosvernier, Philippe
    ;
    Gobat, Jean-Michel 
    ;
    Visconti, Guido
    ;
    Beniston, Martin
    ;
    Iannorelli, Emilio D
    ;
    Barba, Diego
    A brief overview of an attempt to link the effect of elevated CO2 and nitrogen deposition on litter quality and decomposition in a Sphagnum peat bog is given. Litter of three common species (Eriophorum vaginatum, Polytrichum strictum and Sphagnum fallax) was collected from field plots after two years of pre-treatment in two parallel experiments: a) Elevated atmospheric CO2 experiment, b) mineral nitrogen fertilisation experiment. The litters were put into litterbags, leached and inserted into field plots for 3 months, where they decomposed under specific treatment. Distinction between effects of initial litter quality and decomposition on mass loss in the bioleaching and/or in field decomposition process could be tested using a particular set-up in which cross-effects of pre-treatment and treatment were considered.
  • Publication
    Métadonnées seulement
    Testate Amoebae and Nutrient Cycling with Particular Reference to Soils
    (2010)
    Wilkinson, David M.
    ;
    Mitchell, Edward 
    We asked the following question: Is the lack of attention given to testate amoebae, and other protists, in studies of nutrient cycling justified by their relative unimportance or are we ignoring key players in nutrient cycling and other ecological processes? We review various aspects of the ecology of testates relevant to their role in nutrient cycling. These include their food sources, their population sizes and production ecology, the rate of test breakdown ( and hence recycling of material from testates to other organisms) and non-feeding interactions with other organisms (e.g., mychorrhizae). Much of the relevant published literature dates from the late 1960s to the early 1980s, presumably due to the interest in production ecology and other aspects of ecosystem ecology at this time. There was a reduction in relevant research during the 1980s and 1990s, but there has recently been signs of renewed interest in this area. In addition to reviewing the past literature we suggest new speculations about the role of the evolution of grasses and the rise of the euglyphid testates-mediated by the silica cycle. Our main conclusion is that we currently do not know enough to answer our question about their potential importance! However, there are hints in these data which suggest that testates may be important and should be targeted by future research. Some of the main questions that should be targeted are outlined.
  • Publication
    Métadonnées seulement
    SSU rRNA reveals a sequential increase in shell complexity among the euglyphid testate amoebae (Rhizaria : Euglyphida)
    (2007)
    Lara, Enrique 
    ;
    Heger, Thierry J
    ;
    Mitchell, Edward 
    ;
    Meisterfeld, Ralf
    ;
    Ekelund, Flemming
    The existing data on the molecular phylogeny of filose testate amoebae from order Euglyphida has revealed contradictions between traditional morphological classification and SSU rRNA phylogeny and, moreover, the position of several important genera remained unknown. We therefore carried out a study aiming to fill several important gaps and better understand the relationships among the main euglyphid testate amoebae and the evolutionary steps that led to the present diversity at a higher level. We obtained new SSU rRNA sequences from five genera and seven species. This new phylogeny obtained shows that (1) the clade formed by species of genera Assulina and Placocista branches unambiguously at the base of the subclade of Euglyphida comprising all members of the family Trinematidae and genus Euglypha, (2) family Trinematidae (Trachelocorythion, Trinema, and Corythion) branches as a sister group to genus Euglypha, (3) three newly sequenced Euglypha species (E. cf. ciliata, E. penardi, and E. compressa) form a new clade within the genus. Since our results show that Assulina and Placocista do not belong to the Euglyphidae (unless the Trinematidae are also included in this family), we propose the creation of a new family named Assulinidae. Consequently, we give a family status to the genera Euglypha and (tentatively) Scutiglypha, which become the new family Euglyphidae. The evolutionary pattern suggested by SSU rRNA phylogeny shows a clear tendency towards increasing morphological complexity of the shell characterised by changes in the symmetry (migration of the aperture to a ventral position and/or compression of the shell) and the appearance of specialised scales at the aperture (in families Trinematidae and Euglyphidae). (C) 2007 Elsevier GmbH. All rights reserved.
  • Publication
    Métadonnées seulement
    Changes in testate amoebae (Protists) communities in a small raised bog. A 40-year study
    (2005)
    Kishaba, Keiko
    ;
    Mitchell, Edward 
    We analyzed the testate amoebae communities from two sets of moss samples taken forty years apart ( 1961 and 2001) in the same locations of a peat bog of the Swiss Jura Mountains. Peat Cutting and lateral drainage of Le Cachot bog have caused a clear increase in tree cover, especially near the edges. Changes affecting herbaceous plants, mosses. or soil organisms can be subtle, and may easily be overlooked. We hypothesized that we would see changes in the dominant Sphagnum species and the structure of testate amoebae communities living in the mosses. More specifically, we hypothesized that the frequency of bryophyte and testate amoebae species indicative for dry conditions Would increase and that the frequency of species indicative for wet conditions would decrease. The mean testate amoebae species richness per sample decreased from 11.9 to 9.6, but the overall species richness was identical (33 species) in both years. Three species increased significantly in mean relative abundance: Nebela tincta s.l. (+97 %), Bullinularia indica (+ 810 %), and Cyclopyxis eurystoma (+ 100 %; absent in 1961), while two species decreased significantly: Assulina muscorum (- 63 %) and Euglypha compressa (-93 %). The testate amoebae communities clearly differed among microhabitat types (hummocks, lawns, hollows), but no overall significant change in the community was detectable between the two sampling dates (Mantel test). These results could signify that changes at the microscopic level had already taken place by 1961 and no further overall significant changes in micro-enviromental conditions took place during the 40-year period of this Study. This Would agree with the faster response time usually attributed to microorganisms and would also imply that the bushes and trees may be poor predictors of the response of microorganisms if they are themselves in a non-equilibrium stage. Other possible causes for the lack of overall differences are discussed.
  • Publication
    Métadonnées seulement
    Toward the use of testate amoeba functional traits as indicator of floodplain restoration success
    (2012)
    Fournier, Bertrand 
    ;
    Malysheva, Elena
    ;
    Mazei, Yuri
    ;
    Moretti, Marco
    ;
    Mitchell, Edward 
    Functional traits (FT) offer a new framework to understand the ecology of organisms and overcome taxonomic difficulties that currently limit the study of minute soil taxa. FT are likely to be selected by environmental filters and hence they may provide more direct information on ecosystem characteristics than the species composition of a community. We tested the potential of testate amoeba (TA) functional traits as bioindicators of selected ecosystem processes in the context of a restored floodplain in north-western Switzerland. The floodplain was divided into six functional process zones (FPZs) associated to distinct post-restoration successional stages. We selected TA FT and computed three functional indices: functional richness (FRic), divergence (FDiv), evenness (FEve), and dispersion (FDis). We then compared the patterns of functional indices and classical diversity indices such as species richness, diversity and evenness. We assessed whether traits converged or were over-dispersed in the different FPZs using a randomization procedure. Finally, we related environmental variables and functional traits using the "Fourth Corner" statistic. This procedure enabled us to highlight relations that can potentially be used for bioindication. Promising candidates include the relationships between shell biovolume and vegetation structure and between shell compression and plant litter input variables. (C) 2011 Elsevier Masson SAS. All rights reserved.
  • Publication
    Métadonnées seulement
    Horizontal distribution patterns of testate amoebae (Protozoa) in a Sphagnum magellanicum carpet
    (2000-5-2)
    Mitchell, Edward 
    ;
    Borcard, D.
    ;
    Buttler, Alexandre
    ;
    Grosvernier, Philippe
    ;
    Gilbert, Daniel
    ;
    Gobat, Jean-Michel 
    The distribution of soil microorganisms is generally believed to be patchy and to reflect habitat heterogeneity. Despite this general rule, the amount of existing data oil species distribution patterns is scarce. Testate amoebae (Protozoa; Rhizopoda) are an important component of soil microbial communities and are increasingly used in ecological and paleoecological studies of Sphagnum-dominated peatlands, but data on the spatial structure of communities are completely lacking. This is an important aspect since quantitative models used for paleoecological reconstruction and monitoring are based on species assemblages. We explored the distribution patterns of testate amoebae distribution in a macroscopically homogeneous Sphagnum carpet, down to a scale of several centimeters. Distributions maps of the species and spatially constrained sample groups were produced. Multivariate and individual spatial autocorrelations were calculated. The importance of spatial structure was quantified by canonical correspondence analysis. Our ultimate goal is to find the finest resolution of environmental monitoring using testate amoebae. The distribution patterns differed among species, resulting in a complex spatial structure of the species assemblage in a whole. Spatial structure accounted for 36% of the total variation of species abundance in a canonical correspondence analysis constrained by spatial variables. This structure was partly correlated to altitude (microtopography) at a very fine scale. These results confirmed the existence of significant broad-and fine-scale spatial structures within restate amoebae communities that could in parr be interpreted as effects of ecological gradients. This shows that, on a surface area of 0.25 m(2), ecological conditions which look uniform from a macroscopic point of view are not perceived as such by Sphagnum-inhabiting organisms. Therefore, restate amoebae could prove very useful to monitor fine-scale ecological processes or disturbances. Studies of the species' spatial distribution patterns in combination with autoecological studies are needed and should be included in the toolbox of biomonitoring itself.