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Gobat, Jean-Michel

Nom
Gobat, Jean-Michel
Affiliation principale
Fonction
Professeur honoraire
Email
jean-michel.gobat@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/220
_
0000-0003-2967-5178

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  • Publication
    Accès libre
    Structure of microbial communities in Sphagnum peatlands and effect of atmospheric carbon dioxide enrichment
    (2003)
    Mitchell, Edward 
    ;
    Gilbert, Daniel
    ;
    Buttler, Alexandre
    ;
    Amblard, Christian
    ;
    Grosvernier, Philippe
    ;
    Gobat, Jean-Michel 
    Little is known about the structure of microbial communities in Sphagnum peatlands, and the potential effects of the increasing atmospheric CO2 concentration on these communities are not known. We analyzed the structure of microbial communities in five Sphagnum-dominated peatlands across Europe and their response to CO2 enrichment using miniFACE systems. After three growing seasons, Sphagnum samples were analyzed for heterotrophic bacteria, cyanobacteria, microalgae, heterotrophic flagellates, ciliates, testate amoebae, fungi, nematodes, and rotifers. Heterotrophic organisms dominated the microbial communities and together represented 78% to 97% of the total microbial biomass. Testate amoebae dominated the protozoan biomass. A canonical correspondence analysis revealed a significant correlation between the microbial community data and four environmental variables (Na+, DOC, water table depth, and DIN), reflecting continentality, hydrology, and nitrogen deposition gradients. Carbon dioxide enrichment modified the structure of microbial communities, but total microbial biomass was unaffected. The biomass of heterotrophic bacteria increased by 48%, and the biomass of testate amoebae decreased by 13%. These results contrast with the absence of overall effect on methane production or on the vegetation, but are in line with an increased below-ground vascular plant biomass at the same sites. We interpret the increase in bacterial biomass as a response to a CO2-induced enhancement of Sphagnum exudation. The causes for the decrease of testate amoebae are unclear but could indicate a top-down rather than a bottom-up control on their density.
  • Publication
    Accès libre
    Structure of microbial communities in Sphagnum peatlands and effect of atmospheric carbon dioxide enrichment
    (2003)
    Mitchell, Edward 
    ;
    Gilbert, Daniel
    ;
    Buttler, Alexandre
    ;
    Amblard, Christian
    ;
    Grosvernier, Philippe
    ;
    Gobat, Jean-Michel 
    Little is known about the structure of microbial communities in Sphagnum peatlands, and the potential effects of the increasing atmospheric C02 concentration on these communities are not known. We analyzed the structure of microbial communities in five Sphagnum-dominated peatlands across Europe and their response to C02 enrichment using miniFACE systems. After three growing seasons, Sphagnum samples were analyzed for heterotrophic bacteria, cyanobacteria, microalgae, heterotrophic flagellates, ciliates, testate amoebae, fungi, nematodes, and rotifers. Heterotrophic organisms dominated the microbial communities and together represented 78% to 97% of the total microbial biomass. Testate amoebae dominated the protozoan biomass. A canonical correspondence analysis revealed a significant correlation between the microbial community data and four environmental variables (Na+, DOC, water table depth, and DIN), reflecting continentality, hydrology, and nitrogen deposition gradients. Carbon dioxide enrichment modified the structure of microbial communities, but total microbial biomass was unaffected. The biomass of heterotrophic bacteria increased by 48%, and the biomass of testate amoebae decreased by 13%. These results contrast with the absence of overall effect on methane production or on the vegetation, but are in line with an increased below-ground vascular plant biomass at the same sites. We interpret the increase in bacterial biomass as a response to a C02-induced enhancement of Sphagnum exudation. The causes for the decrease of testate amoebae are unclear but could indicate a top-down rather than a bottom-up control on their density.
  • Publication
    Métadonnées seulement
    Can testate amoebae (Protozoa) and other micro-organisms help to overcome biogeographic bias in large scale global change research?
    (: Kluwer Academic Publishers, 2001)
    Mitchell, Edward 
    ;
    Gilbert, Daniel
    ;
    Butler, Alexandre
    ;
    Grosvernier, Philippe
    ;
    Albinsson, Christer
    ;
    Rydin, Hakan
    ;
    Buttler, Alexandre
    ;
    Heijmans, Monique
    ;
    Hoosbeek, Marcel
    ;
    Greenup, Alisson
    ;
    Foot, Jonathan
    ;
    Saarinen, Timo
    ;
    Vasander, Harri
    ;
    Gobat, Jean-Michel 
  • Publication
    Accès libre
    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.
  • Publication
    Métadonnées seulement
    Testate amoebae (Protozoa) and other micro-organisms in Sphagnum peatlands: biogeography, ecology and effect of elevated CO2
    (2000)
    Buttler, Alexandre
    ;
    Heijmans, Monique
    ;
    Rydin, Hakan
    ;
    Hoosbeek, Marcel
    ;
    Mitchell, Edward 
    ;
    Vasander, Harri
    ;
    Gilbert, Daniel
    ;
    Grosvernier, Philippe
    ;
    Albinsson, Christer
    ;
    Greenup, Alisson
    ;
    Foot, Jonathan
    ;
    Saarinen, Timo
    ;
    Gobat, Jean-Michel 
  • Publication
    Accès libre
    Horizontal Distribution Patterns of Testate Amoebae (Protozoa) in a Sphagnum magellanicum Carpet
    (2000)
    Mitchell, Edward 
    ;
    Borcard, Daniel
    ;
    Buttler, Alexandre J.
    ;
    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 on 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 testate amoebae communities that could in part be interpreted as effects of ecological gradients. This shows that, on a surface area of 0.25 m2, ecological conditions which look uniform from a macroscopic point of view are not perceived as such by Sphagnum-inhabiting organisms. Therefore, testate 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.
  • Publication
    Métadonnées seulement
    Can testate amoebae (Protozoa) and other micro-organisms help to overcome biogeographic bias in large scale global change research?
    (: Springer, 1999)
    Mitchell, Edward 
    ;
    Gilbert, Daniel
    ;
    Butler, Alexandre
    ;
    Grosvernier, Philippe
    ;
    Albinsson, Christer
    ;
    Rydin, Hakan
    ;
    Heijmans, Monique
    ;
    Hoosbeek, Marcel
    ;
    Greenup, Alisson
    ;
    Foot, Jonathan
    ;
    Saarinen, Timo
    ;
    Vasander, Harri
    ;
    Gobat, Jean-Michel 
    ;
    Visconti, Guido
    ;
    Beniston, Martin
    ;
    Iannorelli, Emilio D
    ;
    Barba, Diego
    To monitor global change, large scale long term studies are needed. Such studies often focus on vegetation, but most plant species have limited distribution areas. Micro-organisms by contrast are mostly cosmopolitan in their distributions. To study the relationships between organisation groups, we analysed the testate amoebae (Protozoa), vegetation, and water chemistry of five Sphagnum peatlands across Europe. Inter-site differences were more pronounced for the vegetation than for testate amoebae species assemblage. Testate amoebae represent a useful tool in multi-site studies and environmental monitoring of peatlands because: 1) the number of species is much higher than for plants, 2) most species are cosmopolitan and are therefore less affected by biogeographical distribution patterns than plants; thus differences in restate amoebae assemblages can be interpreted primarily in terms of ecology, 3) restate amoebae can be used to analyse and monitor small scale (cm) gradients that play a major role in the functioning of peatland ecosystems. We further studied the effect of elevated CO2 on microbial communities in the same peatlands. Elevated COL increased the biomass of heterotrophic bacteria and decreased the biomass of medium size protozoa (mostly small restate amoebae). These effects suggest changes in community functioning that may have feedback effects on other components of the ecosystem.